Unit cell parameters and structural details of the laboratory synthesised 3NACL single crystal was determined by Single crystal XRD analysis using Bruker Kappa Apex II Diffractometer. From the XRD result, the synthesised 3NACL crystals are belongs to centrosymmetric space group P1 with triclinic crystal system. The single crystal XRD parameters are a=6.8913Å; b=7.8801Å; c=14.6259Å, α=87.021°, β=81.392°, γ=73.231° and V=761.32 Å3. The procured crystallographic values are in good consensus with the reported structural values are depicted in Table 1[10].
Table 1 XRD result of 3NACL single crystal
Parameter
|
Reported result [10]
|
Present result
|
Empirical formula
|
C6H7N2O2+.Cl-
|
C6H7N2O2+.Cl-
|
a(Å)
|
6.9936
|
6.8913
|
b(Å)
|
7.8608
|
7.8801
|
c(Å)
|
14.6708
|
14.6259
|
α≠ β≠ γ
|
87.079°≠81.813°≠73.597°
|
87.021°≠81.392°≠73.231°
|
Volume (Å3)
|
765.77
|
761.32
|
System
|
triclinic
|
triclinic
|
Space group
|
P1
|
P1
|
3.2 FTIR analysis
FTIR analysis was used to identify the function groups present in the compound. Here, Perkin Elmer Spectrum Two FTIR Spectrometer is used to record the FTIR Spectrum of 3NACL. Figure 3 depicted the recorded FTIR Spectrum of 3NACL. From the recorded FTIR spectrum, the N-H asymmetric stretching frequency which almost overlaps with aromatic C-H asymmetric stretching vibration exhibits a band at 3098 cm-1 [11]. The overtones and combined bands are noticed in the range 2003-1697 cm-1. The sharp peak was appeared at 1626 cm-1 due to the present of N-H bending vibration. NO2 asymmetric stretching vibration and the corresponding symmetric stretching vibration was observed at 1500 cm-1 and 1346 cm-1. The strong peak at 1251 cm-1 assigned to NH3+ inplane bending vibration. The prominent peak was obtained at 1086 cm-1 due to the presence of C-N stretching vibration respectively.
3.3 Hirshfeld surface analysis
The intermolecular interactions of the 3NACL was investigated through Hirshfeld surface (HS) [12] and the associated 2D-fingerprint plot (FP) [13] analysis using Crystal Explorer 3.1 [14]. The cif file of the 3NACL crystal is the input file for the Crystal Explorer 3.1 software. HS mapped with different properties de, di, dnorm, shape index and curvedness are provided the good information for the intermolecular interactions and crystal packing of the 3NACL crystal molecules [15]. Nearest nucleus outside and inside the surface is denoted as de and di. In the HS analysis, the red region denotes the negative dnorm value (closer intermolecular interactions) and blue region denotes the positive dnorm value (longer intermolecular interactions). The dominant H…H interaction in the title compound is noticeable as a dark red spot in dnorm, while the dim red spot is due to Cl—H…O interaction. The Hirshfeld surfaces of 3NACL molecule are depicted in Fig. 4.
Plotting between di versus de was gave the two dimensional fingerprint plot, reproduced from the Hirshfeld surface, which conclude the intermolecular contacts. The overall 2D-fingerprint plot for the 3NACL and those attributed into H…H, Cl…H/H…Cl and C…O/O…C interaction were depicted in Fig. 5. From the fingerprint plot H…H & H…Cl interactions are strong and C…C interaction is very low in 3NACL molecule. Especially H…H interaction is above 40%. Due to the high hydrogen bond interaction 3NACL molecules are brilliant candidate for NLO and optoelectronic device fabrications.
3.4 UV- Visible analysis
Perkin Elmer Lambda 35 UV-Visible spectrometer is an instrument used to record the UV-Visible spectrum. Recorded UV-Visible spectrum of the 3NACL crystal is used to study the optical behaviour of the crystal. From the transmittance spectrum (Fig. 6) the cut of wavelength is 276nm due to the intramolecular charge transfer between the electron rich donor amine group to the electron deficient acceptor nitro group. The grown crystal exhibits 83% transmittance depicted its excellent transparency, purity and structural perfection.
Due to the intra molecular charge transfer and high transmittance 3NACL crystals are used to fabricate NLO and optoelectronic device.
The graph was plotting between direct band gap (αhν)2 vs. Photon energy (hν) gives the optical band gap energy of the 3NACL single crystal as depicted in Fig. 7. Then the linear region of the curve was extra plotting to the x axis (photon energy) [16]. Here, the band gap energy of the 3NACL crystal is 4.5 eV. So, the single crystal of 3NACL is suitable material for optoelectronic device fabrications [17].
3.5 Thermal analysis
The 3NACL powder sample weight 5.38mg was taken in the instrument of Perkin Elmer TG/DTA Thermal analyser to study the thermal properties. The resultant TG/DTA curves of 3NACL is depicted in Fig. 8. From the TG curve, the 3NACL sample was thermally stable up to 110°C. When increasing the heating, the 3NACL was start to decreasing its weight 3.46% from 110°C to 164°C. Further heating, 95.18% of weight loss was obtained at 251°C, which indicates the decomposition point of the 3NACL sample. Finally, only 1.36 of residual mass was obtained at 800°C. In the DTA curve, there are two endothermic peak was obtained. The first peak was obtained at 119°C, which indicates the melting point of the sample and the second peak was obtained at 251°C, which indicates the decomposition point of the 3NACL sample. The sharpness of the endothermic peaks denotes the purity and high crystallinity of the 3NACL single crystal. Especially, the decomposition point of the DTA curve was perfectly coincide with the TG curve, and there is no phase transition till the sample get melt, which informs 3NACL crystal was excellent candidate for NLO application up to the limiting of 110°C.
3.6 Vickers microhardness analysis
Shimadzu HMV-2T Vickers microhardness testing device is an instrument used to estimate the mechanical property of the 3NACL single crystal. Mechanical properties of the crystals play the dominant role in fabrication of the optical and electrical devices. Figure 9a depicted the plot between hardness number HV and load P. From the plot, the hardness number increases with applied load due to the reverse indentation size effect (RISE) [18]. The work hardness coefficient (n) of 3NACL material was calculated by plotting a graph between log P& d and the slope drawn, it gives the n value as 2.73(Fig. 9b). The work hardness coefficient value is above 2, so the 3NACL single crystal belongs to the soft material according to Onitsch [19] statement.
The mechanical property of synthesised 3NACL crystal, such as Yield strength (σy), Elastic stiffness constant (C11), fracture toughness (Kc) and Brittleness index (Bi) were calculated [20] in Table 2 for different loads and their respected plots were drawn as depicted in Fig. 10 (a, b, c & d) respectively. In the Elastic stiffness graph (Fig. 10b), it is noticed that the C11 increases with increase in load, which specifies that the binding of the neighbouring atoms are very strong.
In the fracture toughness graph (Fig. 10c), it inspected that fracture toughness increases with load increases, which designated that the grown 3NACL crystal has good mechanical stability. From the Fig. 10d, it is monitored that Bi decreases with increasing the applied load, which stipulated that 3NACL is suitable for various device fabrications. Hence, laboratory synthesis 3NACL single crystals are mechanically stable and acceptable for different NLO material device fabrications
Table 2 Mechanical parameters of grown 3NACL crystal
Load P
(g)
|
HV
(Kg/mm2)
|
σy
(GPa)
|
C11
(×105 GPa)
|
Kc
(×104 Kgm-3/2)
|
Bi
(m-1/2)
|
25
|
52.3
|
11.14
|
10.17
|
3.13
|
167.09
|
50
|
65
|
13.85
|
14.88
|
6.25
|
103.94
|
100
|
93.35
|
19.87
|
28.03
|
12.50
|
74.68
|
3.7 Dielectric studies
LCR impedance analyser is an instrument used to examine the electrical property of the synthesised 3NACL single crystal in the frequency range of 1 KHz to 2 MHz and different temperature at 333K, 353K and 373K. Figure 11(a) & 11(b) was depicted the graph plotting between the dielectric constant (εr) and dielectric loss (tanδ) of the grown 3NACL crystal with log frequency at different temperature. From the Fig. 11a, it is seen that the dielectric constant is relatively high in the lower frequency region, due to the contribution of space charge polarization. It is clear from Fig. 10b that the Dielectric loss (tanδ) should be maintained as low as possible in the higher frequency region, while the material was probable applicant for NLO and micro-electrical device applications [21]. In the Fig. 11c depicted the plot between the ac conductivity (σac) and log frequency of 3NACL material. From the ac conductivity graph, it is noticed that ac conductivity increases with applied frequency increases, which designated that the grown 3NACL crystal was suitable material for fabrication of optoelectronic devices.
Dielectric solid state parameters
The Dielectric solid state parameters play an important role in the fabrication of electronic device industries. Here, the theoretical parameters such as Plasma energy hωp (eV), Penn gap energy EP(eV), Fermi energy EF(eV), Electronic polarizability α (cm3) were estimated [22] and the resultant values were tabulated (Table 3) for the 3NACL material. The good value of polarizability forecasts that the 3NACL material was felicitous candidate for the electronic device fabrications.
Table 3 Dielectric solid state parameters of 3NACL crystal
Parameters
|
Values
|
Plasma energy hωp (eV)
|
20.77
|
Penn gap energy EP(eV)
|
4.65
|
Fermi energy EF(eV)
|
16.83
|
Electronic polarizability (α) using Penn
analysis (cm3)
|
3.93×10-23
|
Electronic polarizability (α) using Clausius-
Mossotti equation (cm3)
|
4.11×10-23
|
3.8 Laser damage threshold study
Now a day’s laser and the technologies play a prominent role in multi-mode application. Laser damage threshold (LDT) is one of the laser technology studies to inspect the surface tolerance of crystal under the laser beam. This surface tolerance capacity of the 3NACL was inspected by using Q-switched Nd: YAG laser (wavelength=1064nm, pulse width=6ns, repetition rate=10 Hz). Optical microscope image of laser damage surface part of the 3NACL single crystal was shown in Fig. 12. The LDT value was calculated using the relation, Power density Pd = E/τA GW/cm2, where E is the energy (mJ), τ is the pulse width (ns) and A is the area of the circular spot (cm2) [23]. The calculated LDT value of the 3NACL crystal was 4.3 GW/cm2. The higher value of the LDT value indicates that the grown material was brilliant candidate for laser weapon fabrication.
Z-scan study was used to examine the third-order NLO property of the materials. Generally, centrosymmetric crystals are not obeyed the second-order NLO property. It only obeys the third-order NLO property. 3NACL single crystals having centrosymmetric space group P1 from the XRD analysis. In this situation, the title compound only obeys the third-order NLO property. So, third-order NLO property of the 3NACL was examined by closed and open aperture z-scan technique [24]. Here, 532nm wavelength Nd: YAG laser beam was used. The third-order nonlinear refractive index η2, nonlinear absorption coefficient (β) and the third-order nonlinear susceptibility (χ3) of the 3NACL compound in ethanol at 0.5mM concentration and 0.48 GW/m2 intensities were calculated [25]. In an open aperture curve, laser intensity increased the transmittance also increased. So, β is positive due to the presence of saturation absorption (SA). In closed aperture curve, normalized transmittance was obtained in valley to peak curve. So, η2 is positive due to the self-focusing. Fig. 13a&13b depicted the open and closed aperture plot of 3NACL crystal respectively. Finally, estimated third order nonlinear optical parameters are reported in Table 4. From the obtained results, 3NACL crystals are promising candidate for photo sensors and all third-order nonlinear optical application.
Table 4 Third order NLO parameters of 3NACL sample
Third-order NLO parameters
|
values
|
Nonlinear refractive index (η2)
|
5.6931(x10-19) (m2/W)
|
Nonlinear absorption coefficient (β)
|
7.5472(x10-12) (m/W)
|
Real part of the third-order susceptibility [Re χ3]
|
2.6411 (x10-13) (esu)
|
Imaginary part of the third-order susceptibility [Im χ3]
|
1.3121 (x10-13) (esu)
|
Third-order nonlinear optical susceptibility [χ3]
|
2.9491(x10-13) (esu)
|