Impact of Ag2O on the mechanical and shielding features of ZnO- Er2O3-TeO2 glasses

doi:10.21203/rs.3.rs-1249950/v1

The investigation involves a comprehensive study on the mechanical and shielding features of the zinc erbium tellurite glasses as a function of doped Ag₂O content. The mechanical features are estimated for the examined glasses by utilizing the Makishima-Makinzie model. The results showed the mechanical moduli of Young (E), bulk (B), Shear (K), and longitudinal (L) increased with the increment of the Ag₂O substitution ratio. Besides, the radiation shielding properties were also studied and discussed. Among the shielding parameters, the linear attenuation coefficient (LAC), half-value layer (HVL), the lead equivalent and transmission rate (TR) were estimated. The linear attenuation coefficient results illustrated that the TZEAg glasses are better compared to the commercial marketing glasses, especially TZEAg5 glasses. Doping of Ag₂O content in zinc erbium tellurite glass improves its ability to attenuate the gamma photons. Also, this study revealed the effectiveness of the examined glasses on the fast neutron, where the fast neutron mass removal cross-section ∑_R (cm²/g) computed theoretically. The results offered the maximum value of ∑_R= 0.019 cm²/g attained for TZEAg1 while the minimum value ∑_R= 0.01884 cm²/g for TZEAg5 glass.

mechanical properties

Monte Carlo simulation

shielding features

tellurite glasses

cross section

Gamma-ray shielding is a very important topic across a wide range of technologies in industries ranging from medical imaging and healthcare to radiotherapy, research facilities and nuclear energy. Several principles have been developed to control the exposure to radiation doses, and one of the most popular principles is ALARA which strives to reduce the exposure of the radiation to the environment and humans [1, 2]. Considering the social and economic factors, consulting with a protection materials expert is extremely important to develop efficient solutions to the shielding needs. The choice of shielding material depends on the kind of radiation that is present. The atoms of the shielding materials interact differently with different kinds of radiation. For instance, lead is capable to shield gamma photons efficiently, but it is quite ineffective for shielding from neutrons. In general, dense materials such as lead, tungsten, heavy metal oxide glasses and certain types of alloys are the strongest in abating the gamma photons. Some types of concretes and polymers are also good materials for blocking neutron radiation [3–9]. Practically, selecting the suitable material allow the manufacturer to utilize a smaller amount of material which can save space. For example, a glass shield with relatively high density would only occupy a quarter or half of the space occupied by a commercial glass with similar attenuation ability. Transparency of a medium is also an important factor when choosing the shielding material for eyeglasses or window glasses used in the X-ray rooms. Other important factors to be considered when selecting the shielding materials are the environmental conditions, the cost of the materials, ease of shipping, handling, and installation. When planning to protect people and workers in the medical and industrial fields from radiation, the attenuation properties of different materials need to be known and the most appropriate material that provides the appropriate radiation protection should be chosen. The aforementioned factors must be considered when selecting the right medium as accurate determination of the shielding factors for different materials is an important part of any radiation shielding plan [10–12]. Cheap and eco-friendly glasses, with interesting optical and physical features, are a good choice to manufacture novel radiation shielding products. Different researchers are trying to develop a variety of thicknesses and sizes of several glass systems that is outstanding in providing radiation protection [13–19]. Radiation shielding glasses are used extensively in dental clinics, radiation therapy rooms, operating theatres, laboratories, veterinary clinics and different materials testing.

TeO₂ glasses, one of the most common glasses, hold technological and scientific importance because of their distinctive features which include good chemical durability, high refractive indices, interesting optical properties, good semiconducting properties and high dielectric constant. Also, it is reported that TeO₂ glasses have relatively high density and thus possess a good attenuation ability against gamma radiation [20–22]. During the preparation process of the TeO₂-based glasses, some glasses modifiers such as ZnO and Ag₂O are used to enhance their optical features and radiation attenuation competences [23, 24]. Introducing the Er₂O₃ ions enhances the chemical durability of glass as well as the radiation shielding features. Therefore, the chance for the TeO₂ glasses with Er₂O₃ to be used in several applications fields such as glass fibers optoelectronics and medical applications is promising [25, 26].

One of the most extensively used techniques for the evaluation of radiation shielding glasses performance is Monte Carlo simulation (MC) [27–29]. MC is an excellent method to study the physical and radiation shielding parameters in case the experimental preparations are difficult or limited to reach. Accordingly, this investigation is aimed to detect the mechanical, and radiation shielding features of a glass system containing TeO_2, ZnO, Er₂O₃ and Ag₂O compounds. The Makishima-Mackenzie (M-M) model is utilized to examine the mechanical features. Moreover, the Monte Carlo N-particle transport code (MCNP-5) was applied to determine the properties of radiation shielding for the studied glass system.

2.1. Mechanical properties

Studying the hardness and elastic properties of the glasses is vital to achieving proper implementation of shielding materials. Therefore, the mechanical features and elastic moduli were theoretically determined for the glass system containing the TeO₂, ZnO, Er₂O₃ and Ag₂O compounds with different ratios using the M-M model. The chemical composition (mol %), density (ρ, g/cm³), and molar volume (V_M, cm³/mol) of the synthetic glass samples were tabulated in Table 1 [30]. Beginning from the constating compounds dissociation energy Gi, the total dissociation energies (Gt, kJ/cm³) were computed for the examined glass samples. The packing factor (Vi, cm³/mol) was also estimated for the studied TZEAg glasses. The packing density (V_t) depends on The molecular weight (M_W, g/mol), the molar fraction (x_i), and the predicted values for V_i where V_t= (ρ/Mw) ∑v_i x_i. Then, the elastic moduli Young (Y, GPa), bulk (B, GPa), shear (S, GPa), and longitudinal (L, GPa) were computed by utilizing the expected values of Vt and Gt, where Y=2V_tG_t, B=1.2 Vt Y, S=(3EB)/(9B-E), and L=B+0.75S. Furthermore, the Poisson ratio (σ) estimated from σ = 0.5-0.1388V_t and the micro hardness (H, GPa) based on the calculated σ values, where H= (1-2 σ)/ (6(1 + σ)). The softening temperature (Ts), ultrasonic velocities (V_l and V_s), and fractal bond connectivity (d) were estimated as well [31].

Table 1

Chemical composition, density, molar volume of TZEAg glass samples.
	Chemical composition (wt %)
	TZEAg1	TZEAg2	TZEAg3	TZEAg4	TZEAg5
Ag₂O	1.58	3.14	4.68	6.20	7.71
Er₂O3	10.32	10.15	9.99	9.83	9.67
TeO₂	72.30	71.16	70.03	68.91	67.80
ZnO	15.80	15.55	15.30	15.06	14.82
Molecular weight	146.85	147.70	148.56	149.42	150.28
Molar volume	32.85	32.25	31.54	31.00	30.24

2.2. Shielding capacity

The MCNP-5 code was employed to detect the protection factors of the TZEAg glass samples. The released photons average track length (ATL) was simulated in the energy interval between 0.240 and 1.408 MeV. An input file was built to reach the essential target. An input file was created to achieve the required target. Figure 1 exhibited the 3D geometry that represents the generated input file. The 3D geometry demonstrates a large lead cylinder with a maximum of 500 mm and a diameter of 200 mm. This cylinder is applied to block the photons from leaving outside the geometry and shield geometry from the surrounding background radiations. Inside this big cylinder, the source of radioactive was installed in the center of this cylinder at point (0, 0, 0). The type of source, radioactivity distribution, dimensions, and emission direction were added to the source card (SDEF). The photons released by the radioactive source were directed to the TZEAg glass samples utilizing a cylindrical collimator of lead with the highest of 70 mm and diameter of 10 mm. The collimator includes a vertical slit with a diameter of 10 cm to collimate the emitted photons. The chemical composition and density of the examined glass samples were noted in Table 1. The glass samples were presented to the input file as a small cylinder with a diameter of 15 mm and various thicknesses. The detector applied in the immediate simulation has a type of F4 which is tally to predict the number of photons incident per unit detector cell. The NPS was set up to prevent the interaction after 106 historical. The MCNP-5 code employs the primary cross-section data sources ENDF, ACTI, ENDL, ACTI, and T-16 files [32].

The simulated ATL was transferred to the linear attenuation coefficient (LAC, µ). Based on the LAC for the synthesized TZEAg glasses, the transmission rate (TR) was calculated to describe the ratio of photons penetrated the glass thickness, where TR= (1- (I/I_o)). Io and I represent the gamma-ray intensities' values before and after passing the glass thickness [33, 34].

3.1. Mechanical and physical properties

The fabricated glass of ρ (cm²/g) and V_m (cm³/mol) were plotted against the Ag₂O insertion content, as illustrated in Figure 2. The ρ values increased systematically between 4.47 and 4.97 g/cm^3, while the V_m decreased in values between 32.85 to 30.24 cm³/mol, with increasing Ag₂O insertion ratio from 1 and up to 5 mol%. As the substitution process occurred by the TeO₂-ZnO-Er₂O₃ with Ag₂O content, the progress detected in density is due to the partial replacement of TeO₂, ZnO, and Er₂O₃ with respective densities of 5.67, 5.61, and 8.64 g/cm³ by Ag₂O, which has a density around 7.14 g/cm³.

The measured values of ρ, molecular weight (M, g/mol), and heat of formation (enthalpy) for the glass constating compounds were used to evaluate the constating compounds dissociation energy (G_i, kJ/cm³). After that, the total dissociation energy (G_t, kJ/cm³) was calculated, where G_t=∑x_iG_i, x_i represents the constituting compound's molar fraction. The packing factor (V_i, cm³/mol) was also calculated based on each constituting element's ionic radius. The change in V_i and G_t with the Ag₂O insertion ratio was presented in Figure 3. The V_i values were slightly changed from 13.074 to 13.095 cm³/mol while the G_t decreased from 53.348 to 52.291 kJ/cm³ when Ag₂O partially replaced the TeO₂, Er₂O₃, and ZnO. This behavior is due to the substitution of a small number of Te-O, Zn-O, and Er-O bonds with Ag-O bonds. The bond dissociation energy of the Te-O, Zn-O, Er-O are 354, 284.1, and 611 kJ/cm³, while it is 213 kJ/cm³ for Ag-O. Thus, the G_t decreases with increasing the Ag₂O content in the fabricated glass samples.

Based on the estimated values of V_i and G_t, the mechanical moduli Young (E), bulk (B), Shear (K), and longitudinal (L) were predicted. Figure 4 displays the change in E, B, K, and L as a function of the Ag₂O content. All of the mechanical moduli are slightly increased with increasing the Ag₂O substitution ratio. The mechanical moduli are slightly increased between 42.460 -45.393 GPa, 20.277-23.538 GPa, 18.445-19.203 Gpa, and 44.870-49.142 GPa for E, B, K, and L moduli, respectively. The slight increase in the mechanical moduli is due to Vi and Gi values with slight variation as the Ag₂O replaced the TeO₂, ZnO, and Er₂O₃. The mechanical properties predicted using the M-M model were compared to those measured experimentally by Halimah et al., (2019) [35] and illustrated in Table 2. The data listed in Table 1 showed agreement between the experimental and M-M model results. This confirms the ability of the M-M model to predict the mechanical properties of such glass systems.

Table 2

The Mechanical and elastic properties were measured experimentally and estimated using the M-M model.
	E (GPa)		B (GPa)		K (GPa)		L (GPa)		σ		H
	Exp	M-M model	Exp	M-M model	Exp	M-M model	Exp	M-M model	Exp	M-M model	Exp	M-M model
TZEAg1	47.60	42.46	28.69	20.28	19.48	18.45	54.67	44.87	0.22	0.15	3.60	4.29
TZEAg2	50.24	43.06	34.47	20.95	19.98	18.60	61.11	45.75	0.25	0.16	3.24	4.25
TZEAg3	45.94	43.82	26.29	21.81	19.00	18.80	51.63	46.89	0.20	0.17	3.65	4.20
TZEAg4	44.78	44.38	24.20	22.49	18.79	18.95	49.25	47.75	0.19	0.17	3.87	4.16
TZEAg5	49.12	45.29	39.22	23.54	19.02	19.20	64.58	49.14	0.29	0.18	2.65	4.11

The values of σ and H are calculated based on the elastic moduli and displayed in Figure 5. The σ increased from 0.15 to 0.18, while the H values decreased from 4.29 to 4.11 GPa with increasing the Ag₂O substituting TeO₂-ZnO Er₂O₃ in the fabricated glass samples. The detected behavior is due to the replacement of many Te-O, Zn-O, Er-O bonds by Ag-O bonds.

The predicted values for shear and longitudinal moduli were utilized to calculate the shear velocity (ν_s) and longitudinal velocity (ν_l) where ν_l= (L/ρ)^0.5 and ν_s= (K/ρ)^0.5. The calculated values of ν_l showed that it takes values of 3168, 3160, 3155, 3147 and 3144 m/s for glass samples with 1, 2, 3, 4, and 5 mol % of the Ag₂O content. Also, ν_s takes values of 2031, 2015, 1998, 1982 and 1965 for the same glass samples. The calculated values for ν_l and ν_s showed agreement with the experimental values reported by Halimah et al., (2019) [35]. For almost all samples except for glass with 2 mol % of the Ag₂O, the experimental results have higher values than the theoretical results.

The fractal bond connectivity (d) is a critical parameter relating to the structure and derived by Bergman and Kantor [36]. It describes information about the glass dimensionality and network crosslinks. The calculated d values are 3.64, 3.55, 3.45, 3.37, and 3.26 for glasses TZEAg1, TZEAg2, TZEAg3, TZEAg4, and TZEAg5, respectively. The presented d values are closed to 3. Thus, the fabricated glasses have a 3D layer structure, as reported in ref [37]. In this regard, the evaluated d values were compared to those based on experimental measurements. There is an agreement between the theoretical and experimental d values for glass samples TZEAg1, TZEAg3, and TZEAg4. Still, there is a disagreement for glasses TZEAg2 and TZEAg5, where the experimental measurement showed that these glasses are 2D layer structure glasses.

3.2. Shielding features of the studied glass

In recent years the different materials are developed for radiation protection. Among these materials, the researchers are fabricated and modified several glasses forms to enhancement in their ability to attenuate the gamma and neutron radiation. The ability is measured and detected via many shielding factors such as linear attenuation coefficient (LAC), transmission rate (TR), half-value layer (HVL), lead equivalent thickness and the effective removal cross-section (ERSCFN).

Figure. 6 offers the variation of LAC with the incident gamma photon energy (E_ϒ) and the chemical composition (Ag₂O content mol %) of the studied glasses. It is balanced in Fig. 6 that the decrement of LAC values affected by the increment on E_ϒ from 0.240 to 1.408 MeV. The high levels are disclosed in the low energy range namely the Photoelectric effect (PE) area. At low energy, 0.240 MeV the LAC rates altered from 1.01 to 1.11 cm⁻¹ for TZEAg1 and TZEAg5, respectively. The attenuate incident photons with low energies increase owing to the PE cross-section where (σ_PE α E^3.5). After that the incident energy E_ϒ continuously elevated but the LAC values diminish where the Compton scattering interactions (CS) are dominant in the energy range above 0.1 MeV. The decrement is banded to the CS cross-section which is directly proportional to the reciprocal of the incident photon energy (σ_CS α E⁻¹). The increment of E_ϒ for several MeVs affects emotionally the LAC values to reach the minimum values where at 1.408 MeV, the values are 0.21 cm⁻¹ and 0.24 cm⁻¹ for TZEAg1 and TZEAg5, respectively.

The doped Ag₂O content in the zinc erbium tellurite glasses also affected by the LAC values at the stationary incident photon energy as displayed in Fig. 6. The LAC values are influenced by the increment of Ag₂O content from 1 to 5 mol % in TZEAg glasses, where the M_w raised from 146.85 to 150.28 g/mol for TZEAg1 and TZEAg5, respectively but Z_eff diminished. For instance, the LAC values for the investigated glasses varied progressively in between 0.240 and 1.408 MeV with the following sequences: TZEAg1 (1.01-0.21 cm⁻¹) < TZEAg2 (1.03.5-0.22 cm⁻¹) < TZEAg3 (1.06-0.226 cm⁻¹) < TZEAg4 (1.08-0.0.231 cm⁻¹) < TZEAg5 (1.11-0.240 cm⁻¹). This increment can be associated with the cross-sections PE interactions (σ_PE α\({ Z}_{eff}^{4-5}\), CS interactions (σ_CS α Z_eff) and PP interactions (\({Z}_{eff}^{2}\)). in the studied photon energy ranges. Figure 7 illustrates the difference (Diff %) between the simulated LAC and the calculated using XCOM program. The positive difference was observed at low energy while it increased with the increment of photon energy.

Among the investigated TZEAg glasses, two fabricated (TZEAg1 and TZEAg5) are selected to compare their values of LAC with the commercial SCHOTT market glasses RS253, RS253 G18, RS323 G19, RS 360 and RS 520 [38] at the photon energy of cesium source (0.662 MeV) (Fig. 8). The linear attenuation coefficient (LAC) values for TZEAg1 and TZEAg5 were found to be higher than all commercial glasses except RS 520. Thus, the glasses under study are a candidate for applications in different radiation protection fields.

The half value layer (HVL) is the shielding parameter that was computed to detect the ability of the studied TZEAg glasses to reduce the E_γ in half. The HVL values depend on the E_γ and the density of the investigated glass. Therefore, the materials with the minimum values of HVL are significant and can be employed in the different shielding applications. It is obvious in Fig. 9 that the increment on HVL rates is directly proportional to the elevation of E_ϒ from 0.015 MeV up to 5 MeV. For instance, at the low E_ϒ range (0.015-0.08 MeV), the HVL values of TZEAg glasses increase from 0.003 to 0.045 cm for TZEAg1 and from 0.002 to 0.046 cm for TZEAg5. This displays the HVL values also impacted the addition of Ag₂O content in the zinc erbium tellurite glasses.

As can be seen in Fig. 9, the HVL values diminish in all E_γ values with the insertion of Ag₂O content increases from 1 to 5 mol %. The HVL rates dropped from 0.003 to 0.002 cm for TZEAg1 (density-4.47 g/cm³) and TZEAg5 (density-4.97 g/cm³), respectively. This means that the increase in density of TZEAg glasses leads to the HVL values being reduced. Consequently, TZEAg5 is the best-studied glass material that can be used in shielding applications where the incoming photon will travel for a shorter distance inside the TZEAg5 glass material.

The lead equivalent is a shielding factor describing the ratio of radiation attenuation which fabricated material offered compared to the pure lead element. The lead equivalent was calculated for the fabricated glass samples and presented in Figure 10 as a function of photon energy. Figure 10 showed that the lead equivalent increased with increasing the photon energy between 240 and 1408 keV. This means that the fabricated TZEAg glasses are more shielding effective at the end of the studied range (i.e., 1000 to 1408 keV). The lead equivalent varied between 0.136-0.349, 0.240- 0.358, 0.143- 0.368, 0.146- 0.377, and 0.150 -0.389 for glass samples TZEAg1, TZEAg2, TZEAg3, TZEAg4, and TZEAg5, respectively. The mentioned results also showed that the equivalent lead ratio was enhanced with the addition of Ag₂O content.

The transmission rate (TR) was calculated for the fabricated TZEAg glasses. Figure 11 displays the TR changes versus the Ag₂O content for the TZEAg glasses at different photon energy and glass thickness. Figure 11 depicts that TR values are affected by the gamma photons energy, glass thickness, and modifier type. Gamma photon energy has the highest effect on the transmission rate, where it is increased with an increase the photon energy. The increase in the TR is related to the incoming photons' penetration power, where the penetration power also increased with an increase in the photon energy. Thus, a thicker thickness is required to stop the gamma photons with high penetration powers. The TR increases between 0.0791, 0.427, 0.564, and 0.584 with increasing in photon energy between 240, 662, 1250, and 1406 keV, respectively, for 2.5 cm thickness of the glass TZEAg1. The TR's increase is linearly in the studied energy region due to the Compton Scattering interaction, which is the primary interaction in the investigated energy interval.

The second important factor affecting the TR is the glass thickness, where thicker glasses are better in stopping the incident radiations. The thicker glass layer strongly forced the gamma photons to interact with glass electrons and atoms; producing a high resistance for the passing photons. Thus, the LAC of the studied glass increase, and the photon TR decreases. At gamma-ray energy 662 keV, Figure 9b showed that the TR decreased from 0.698 to 0.166 with the increase of the glass TZEAg3 thickness from 1 to 5 cm.

Also, the modifier type plays a role in reducing or increasing the TR. Figure 11a, b, c, and d illustrate that the replacement of TeO₂, ZnO, and Er₂O₃ by Ag₂O is slightly reduced the TR values. This is related to the effective atomic number (Z_eff) of the fabricated glass samples, where substituting of TeO₂, ZnO, and Er₂O₃ by Ag₂O resulting a slight increase in the Z_eff of the fabricated glass. Thus, the LAC of the fabricated glass increases and the photons TR decreased. The TR at energy 240 keV and thickness 1 cm decreased from 0.362 to 0.327, increasing the Ag₂O between 0 and 5 mol%, respectively.

The fast neutron mass removal cross-section ∑_R (cm²/g) was calculated theoretically for the fabricated TZEAg glass samples, as illustrated in Figure 12a. The ∑_R (cm²/g) takes values 0.01902, 0.01898, 0.01893, 0.01888 and 0.01884 cm²/g for glass samples with 1, 2, 3, 4, and 5 mol% of Ag₂O. The reduction in the ∑_R (cm²/g) is due to the replacement of Te, E, and Zn with Ag. The macroscopic cross-section of Te, Er, and Zn are 0.013408, 0.11522, 0.018648 cm²/g, while the Ag macroscopic cross-section is 0.014196 cm²/g.

Based on the calculated effective removal cross-section for the fast neutron, the removal cross-section ∑_R (cm⁻¹) was calculated and plotted versus the glass density, as presented in Figure 12b. The ∑_R (cm⁻¹) increases in the following order 0.08504, 0.08691, 0.08916, 0.09102, and 0.09362 cm⁻¹ with increasing the glass density between 4.47, 4.58, 4.71, 4.82, and 4.97 g/cm³, respectively. Also, the relaxation length (λ, cm) was calculated and presented in Figure 12c versus the Ag₂O content. The λ values decrease from 11.759 cm to 10.681 cm, increasing with the AgO₂ between 1 and 5 mol%, respectively. This decrease is due to the replacement of lower macroscopic cross-section elements Er, Te by a higher element Ag. Also, the thickness required to absorb the half amount of neutrons is calculated and plotted as a function of the material density. It takes values 8.15, 7.97, 7.77, 7.61, and 7.40 cm for samples TZEAg1, TZEAg2, TZEAg3, TZEAg4, and TZEAg5, respectively.

Structural properties

X-ray diffraction

X-ray diffraction or also called XRD is one of the characterizations that is used to study the structural properties of the glass. In this work, the XRD was employed to identify whether the fabricated glass sample is amorphous or crystalline. The XRD spectra of the glass series are illustrated in Figure 12. The spectra were recorded at room temperature in the range of 20° ≤ θ ≤ 80°.

The XRD spectra as depicted in Figure 12 display a broad diffusion hump at the lower scattering angles proposing the presence of a lack of long-range structural order in the glass samples. The existence of a broad hump around 2θ = 30° or in other words, the absence of a sharp peak ratifies the non-existence of the crystalline phases in the material and affirms that both glass series are completely amorphous [39]. The increasing concentration of the dopant leads to the narrowing of the broad humps. It can also be further studied that the shift of the hump towards a high angle might be due to the lower values of d spacing between atomic levels that decrease the bond length. This statement had been supported by Cai et al. (2016) [40] had also reported that the non-existence of long-range atomic arrangement in the glass system proves the amorphous nature of the glass samples.

Fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) is one of the non-destructive methods which provides information regarding the structure and vibrational properties of the elements that exist in the glass system. Nanda et al., (2015) had also reported that FTIR is one of the methods that can be used in determining the functional group of the elements as well as providing information about the vibrational modes of the molecules which exist in the disordered amorphous materials. The observable transmission bands in FTIR spectra attained for both glass series are in the range of 611-616 cm⁻¹ which is presented in Figure 14. The assignments of the transmission spectra for silver-doped zinc tellurite glasses are tabulated in Table 3. The positions of the valley are related to the tellurite network as mentioned by Azlan et al., (2015) [41].

Table 3

Assignments of the peaks observed in the FTIR spectra of silver-doped erbium zinc tellurite glasses
FTIR peak position (cm⁻¹)	IR assignments
611-616	Stretching vibration of TeO₄ units (Kaur et al., 2016 and Mahesvaran et al., 2013)

The transmission band for the pure structural unit of tellurium oxide (TeO₂) is positioned at 640 cm⁻¹. Nevertheless, tellurium oxide subsists two different types of functional groups which are trigonal pyramid (TeO₃) and trigonal bipyramid (TeO₄) (Pavani et al., 2011). The TeO₃ functional groups correspond to the Te-non-bridging oxygen while TeO₄ corresponds to the Te-bridging oxygen. The transmission bands that lie in a range of 611-616 cm⁻¹ are explained by the presence of the trigonal bipyramid structural unit [42]. This single band is considered to be broadened with the presence TeO₂ structural unit [43]. On the other hand, the variation in the composition of the glass network might also affect the shifting of the functional group in the disordered amorphous material.

Meanwhile, structural units of zinc oxide, erbium oxide ad silver oxide are also not found in the transmission band of the glass system. The zinc lattice in the glass system is said to be broken down which causes the absence structural unit of zinc oxide as an additional functional group. However, at an early stage, the structural unit of zinc oxide will break down the Te-O-Te bonds that subsequently will form coordination effects known as dangling bond (non-bridging oxygen) forming (Te-O⁻…Zn²⁺…O-Te) bonds. Consequently, this will increase the formation structural unit of the trigonal pyramid but in return will reduce more structural units of trigonal bipyramid in the glass system [44]. The presence of both structural units of erbium oxide and silver oxide are also not evidenced which can be associated with low concentration.

Deconvolution technique

The transmittance results are then converted to absorbance data. The absorbance spectra results will be deconvoluted immediately. The deconvolute data will determine the area of every band which corresponds to each element that exists in the glass system. The deconvolution is implemented by using Origin 6.0 software and the result for deconvolution spectra is illustrated in Figure 14.

The FTIR spectra have been deconvoluted to identify the exact peak positions of the structural units which exist in the prepared glass. The peak position (x_c) and amplitude (A) for all the peaks are observed after the deconvolution process. Then, the data is tabulated in Table 4. The assignments for each functional group in every element are attained from the deconvoluted FTIR spectra which are based on the information obtained from the literature done by previous researchers.

Table 4

Assignments of the peaks of erbium-doped and silver-doped zinc tellurite glasses using deconvolution technique
FTIR peak position (cm⁻¹)	IR assignments
642-700	Stretching vibration of TeO₄ units (Kaur et al., 2016 and Mahesvaran et al., 2013)
532-580	Anti-symmetric vibration of Te-O bonds in TeO₃ units (Ayuni et al., 2011 and Noorazlan et al., 2013)
480-560	Stretching vibration of Er-O bonds in Er₂O₃ units (Bosca et al., 2009)
550-560	Stretching vibration of Ag-O bonds in Ag₂O units (Coelho et al., 2012)

Table 5

Band center, B and band area, A of silver-doped erbium zinc tellurite glasses
Ag₂O content	Peak position, B (cm⁻¹) and band area, A (%)
0.01	B	619.29	702.58	499.21	611.93
	A	20.93	40.93	58.40	42.97
0.02	B	665.81	752.44	481.00	596.28
	A	40.65	18.82	81.50	32.13
0.03	B	616.60	683.48	500.35	607.07
	A	27.20	57.02	48.60	21.16
0.04	B	650.32	698.81	520.53	618.89
	A	29.58	28.53	46.75	15.15
0.05	B	659.42	744.12	485.13	592.32
	A	36.00	18.55	69.55	25.51
Assignments		TeO₄	TeO₃	Er₂O₃	Ag₂O

As mentioned earlier, the tellurite-based glasses consist of two structural units which are trigonal pyramid (TeO₃) and trigonal bipyramid (TeO₄). After the deconvolution process, the absorption band for both TeO₃ and TeO₄ groups lies in the range of 532-700 cm⁻¹. The IR bands achieved for TeO₄ stretching vibration are in the range of 532-580 cm⁻¹ [42]. Meanwhile, the structural unit for TeO₃ has been detected to present in the range of 642-700 cm⁻¹ [45–46]. According to Ayuni et al., (2011) [45], the absorption band which lies in the range of 620-660 cm⁻¹ represents the symmetrical vibration of Te-O bonds.

Based on Noorazlan et al., (2013) [46], there is still no presence of ZnO structural unit being formed which consists of ZnO₄ and ZnO₆ after the FTIR spectra have been deconvoluted. As mentioned before, the lattice structural unit of ZnO is broken down which provides no functional group of ZnO in the spectra for both glass series. The structural unit for Er₂O₃ presents in the range around 480 cm⁻¹ and 560 cm⁻¹ respectively. The existence structural unit of erbium oxide in the materials modifies the structure of the tellurite glass network [47] and there is also an existing structural unit of Ag₂O in the glass system which falls in the range of 550-650 cm⁻¹. According to Coelho et al., (2012) [48], the occurrence of shifting bands is due to the presence structural unit of silver oxide which breaks some of the bonds and modifies the structure of the glass system. The increment of both dopants concentration signifies the change of Te-O bond from TeO₄ to TeO₃ which indicates the creation of NBO’s that is followed by the shift of the primary structural unit of TeO₂ to a higher wavenumber. The presence of the TeO₄ structural unit acts as evidence towards the formation of BO’s at the same time.

The concentration of the structural units present in both glass systems can be attained using the following equation [49]:

\({N}_{4}=\frac{{A}_{4}}{{A}_{4}+{A}_{3}}\) (1)

where A₃ and A₄ represent the areas of TeO₃ and TeO₄ units and N₄ is used to determine the concentration units for TeO₄ or vice versa. The concentration of TeO₄ and TeO₃ units which is presented in both glass series are illustrated in Figure 16.

Figure 16 displays the concentration of TeO₄ and TeO₃ structural units against the molar fraction of silver oxide. The deconvolution process has determined the concentration of both TeO₄ and TeO₃ structural units as expressed in Equation 1. The variation of the concentration is attributed to the conversion of the structural units of TeO₄ to TeO₃ and vice versa. The presence of silver-doped zinc tellurite glass contributes to the changes in the tellurite network. Trigonal pyramid (TeO₃) is assigned to the non-bridging oxygen (NBO) which tends to be converted into trigonal bipyramid (TeO₄) structural units or vice versa as more concentration of dopants are included in the glass system. The role of dopants is strongly related to the concentration of trigonal bipyramid and trigonal pyramid structural units.

A series of zinc erbium tellurite glasses doped with silver oxide and based on the chemical formula [[(TeO₂)_0.7(ZnO) _0.3] _0.96 (Er₂O₃)_0.04]] _1-y (Ag₂O) _y where y= 0.01, 0.02, 0.03, 0.04, 0.05 was studied. The Makishima-Mackenzie assumptions are applied to theoretically estimate the mechanical properties. All elastic moduli are observed to increase with the increment of silver oxide content in the TZEAg glasses where Young (E), bulk (B), Shear (K), and longitudinal (L) varied between 42.460-45.393 GPa, 20.277-23.538 GPa, 18.445-19.203 Gpa, and 44.870-49.142 GPa for TZEAg1 and TZEAg5, respectively. The radiation shielding features were also examined for the TZEAg glasses. The LAC values reached the maximum at low energy 0.240 MeV, altered from 1.01 to 1.11 cm^-1 for TZEAg1 and TZEAg5, respectively. The substitution of ZnO, TeO₂ and Er₂O₃ with Ag₂O content in TZEAg glasses enhanced the features for gamma and neutron radiation protection where TZEAg5 is the preferable glass to be used in various radiation shielding equipment.

Acknowledgment

We would like to expand the gratefulness to the authors of the Deanship of Scientific Research at King Khalid University, Saudi Arabia for funding this work through the General Research Program under grant number G.R.P/78/42. We would like to thank Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2022R48), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

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Impact of Ag₂O on the mechanical and shielding features of ZnO- Er₂O₃-TeO₂ glasses

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials And Methods

2.1. Mechanical properties

2.2. Shielding capacity

3. Result And Discussion

3.1. Mechanical and physical properties

3.2. Shielding features of the studied glass

Conclusion

Declarations

Acknowledgment

References

Status:

Version 1