Ultrahigh Permittivity, Ultralow Loss and Stability in (In0.5Ta0.5)0.1Ti0.9O2 Ceramics With Temperature Range From -100 to 235 °C

doi:10.21203/rs.3.rs-1195430/v1

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Ultrahigh Permittivity, Ultralow Loss and Stability in (In_0.5Ta_0.5)_0.1Ti_0.9O₂ Ceramics With Temperature Range From -100 to 235 °C

https://doi.org/10.21203/rs.3.rs-1195430/v1

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Dielectric materials with excellent dielectric properties are being promoted in requirements of microelectronic devices. In this study, (In_0.5Ta_0.5)_0.1Ti_0.9O₂ ceramics were achieved by a solid-state reaction with reducing atmosphere of N₂. Also, dense microstructure, ultrahigh permittivity (ε_r = 1.18 × 10⁵) and ultralow dielectric loss (tanδ = 0.0072) were demonstrated at1 kHz. Interestingly enough, the temperature coefficient of permittivity which satisfies X9D (-100 °C - 235 °C, Δε_r/ε_25°C < ± 3.3 %) maintained stability at 1 kHz, and the dielectric mechanism could be connected to the electron-pinned defect dipoles (EPDD), which has favourable potential applications in electronic devices.

Ceramics

Optical Materials and Devices

ultrahigh permittivity

ultralow dielectric loss

temperature stability

As electronic devices continue to develop towards integration, intelligence and high performance, the development of dielectric materials has become a hot topic, especially the excellent high temperature range above 200°C at the engine compartment of new energy vehicles. Regrettably, it is difficult to develop applicable properties of dielectric materials for such applications. Understanding historical research, plenty of colossal permittivity (CP) materials were synthesized, including the BaTiO₃ ceramics and ACu₃Ti₄O₁₂ (A = Ca, Sr, Bi, Na, Cd) materials [1–4]. Although BaTiO₃ has been reported with excellent dielectric properties, the permittivity of pure BaTiO₃ near Tc which was 120°C fluctuates massively. Recently, a stable dielectric properties at temperature range for X7R (-55 - 125°C, Δε_r/ε_25°C ≤ ±15%) applications were obtained in La³⁺ and Ca²⁺ ions co-doped BaTiO₃ samples with dielectric loss (tanδ = 0.04) and permittivity (ε_r = 2000) by Lu et al [5]. Also, Nb⁵⁺ and Ni²⁺ ions co-doped BaTiO₃ ceramics were investigated for X7R ceramics by Li et al [6]. Li et al. found the BaTiO₃-0.01Nb₂O₅-xMgO ceramics with permittivity (ԑ_r = 4.5 × 10⁴), which merely satisfies the X8R (-55 - 150°C, Δε_r/ε_25°C ≤ ±15%) requirement [7]. On the other hand, Wang et al. reported TiO₂ modified CaCu₃Ti₄O₁₂ ceramics which showed permittivity (ε_r = 6.81 × 10⁴), but over 0.12 dielectric loss at 1 kHz [8]. Peng et al. reported dielectric loss (tanδ = 0.035) of CdCu₃Ti₄O₁₂ ceramics were reported through a sol-gel technique, only for X8R ceramics [9]. The results of the survey show high permittivity, low dielectric loss and excellent temperature stability cannot be achieved at the same time.

It is worth noting that (In_0.5Nb_0.5)_xTi_1−xO₂ ceramics were prepared by Liu et al. using a solid-state method in 2013 [10], and the systems exhibited CP (ԑ_r > 2 × 10⁴) and low dielectric loss (tanδ < 0.05), simultaneously showed good frequency and temperature stability over wide ranges. Li et al. reported the (La_0.5Nb_0.5)_xTi_1−xO₂ samples with dielectric loss (tanδ = 0.02896) and permittivity (ε_r = 49692), but the samples only fulfilled temperature stability for X8R [11]. Peng et al. prepared (Ag_1/4Nb_3/4)_0.005Ti_0.995O₂ ceramics, obtained X9R (-55 - 200°C, Δε_r/ε_25°C ≤ ±15%) requirements, but low permittivity and relatively high dielectric loss are 9410 and 0.037, respectively [12]. In 2017, the (In_0.5Ta_0.5)_xTi_1−xO₂ ceramics were discussed by Hu et al., and the result of the system exhibited excellent dielectric properties with temperature stability from -223 - 127°C for x = 0.005 [13]. Plenty of researches paid attention to the capacitance, loss parameters and others of TiO₂-based ceramics [14–21], but these reported materials which were difficult to balance permittivity, dielectric loss and temperature stability, especially further satisfy the requirements for high temperature industrial application above 150°C.

Compared with Nb⁵⁺ ion, Ta⁵⁺ ion has more one electron shell with the larger distortion resulting in stronger localization of the electron [13], which could result to the lower dielectric loss and more stable permittivity at a wide temperature range. On the other hand, ultrahigh permittivity needs more defect dipole clusters, so the higher permittivity could be obtained in ceramics by sintering in N₂ reducing atmosphere. In this work, the In³⁺ and Ta⁵⁺ co-doped TiO₂ ceramics based on the solid-state reaction method were synthesized in N₂ reducing atmosphere. The excellent dielectric properties with ultrahigh permittivity (1.18 × 10⁵ at 1 kHz), ultralow dielectric loss (0.0072 at 1 kHz) and temperature stability which satisfies X9D (-100°C - 235°C, Δε_r/ε_25°C < ± 3.3%) were exhibited.

The (In_0.5Ta_0.5)_0.1Ti_0.9O₂ (abbreviated by ITTO) ceramics were synthesized using a solid-state reaction process. The prepared materials of TiO₂ (99.99%, rutile, Aladdin), In₂O₃ (99.99%, Aladdin), and Ta₂O₅ (99.99%, Sinopharm) were dried for 24 h in a drying oven at 80°C. Next, these oxides were weighed with stoichiometric compositions and ball-milled in deionized water with zirconia balls for 6 hours. After pulverizing and drying, the powder was calcined at 1150°C in air for 2 hours. What's more, the preprocessed powder was made into pellets using a cold isostatic press. Finally, the samples were sintered at 1450°C for 4 h with N₂ reducing atmosphere.

The phase structure was executed using Raman spectroscopy (Renishaw-invia) and X-ray diffraction (XRD) technique (D8 advance, Germany), and the Rietveld refinement result was fitted using the GSAS software for the ITTO samples. The microstructure of hot-corrosion surface sample was achieved using scanning electron microscopy (SEM) (Regulus 8100, Hitachi). The precision impedance analyzer (Agilent-E4980A) was selected to determine dielectric properties of the ITTO ceramics. The X-ray photoelectron spectroscopy (XPS) (AXIS SUPRA Britain) was used to measure the valence states of the elements which was fitted using the Casa XPS software.

Figure 1(a) exhibited the Raman spectroscopy of ITTO samples, verifying the phase structure of the ceramic. Four characteristic peaks were observed, including B_1g, E_g, A_1g and the second-order effect in multi-phonon peak at 234 cm⁻¹. As a result, the Raman peak which verify the existence of the rutile TiO₂ crystal structure [16]. In terms of the Rietveld refinement, no distinct other phases were observed in ITTO samples in Figure 1(b). The lattice parameters (a = b = 4.614 Å and c = 2.980 Å) of the ITTO ceramics were achieved by Rietveld refinement are larger than ( a = b = 4.593, c = 2.959 (JCPDS 21-1276)) for pure rutile TiO₂ [22]. As a result, the lattice size of the increase could be related to the Ta⁵⁺ and In³⁺ of larger ionic radii instead of the Ti⁴⁺ ions, indicating Ta⁵⁺ and In³⁺ form a complete solid solution in rutile TiO₂ structure. Figure 1(c) exhibited the microstructure of hot-corrosion surface for the ITTO ceramics in detail, and dense sample, apparent grain and grain boundary were observed, no obvious impurity segregation and porosity, and Figure 1(d) exhibited the grain size almost 11.35 µm.

To reveal the dielectric properties in ITTO ceramics, Fig. 2(a) exhibited the frequency dependence of the dielectric loss and permittivity of the ITTO ceramics, which are 0.0072 and 1.18×10⁵ at 1 kHz, respectively, including the good frequency and temperature stability. Meanwhile, Fig. 2(b) exhibited the temperature function of ITTO ceramics. The temperature coefficient of the sample is calculated between ± 3.3% at 1 kHz, which satisfies X9D (-100°C - 235°C, Δε_r/ε_25°C < ± 3.3%), and Fig. 2(c) exhibited between ± 4.7% at 10 kHz, which satisfies X9E (-60°C - 300°C, Δε_r/ε_25°C < ±4.7%) requirements, far below the practical applications requirements. As shown in Fig. 2(d), the typical CP materials have been contrasted in detail. As a result, the ultralow dielectric loss, ultrahigh permittivity with temperature stability were obtained in ITTO ceramics. [5–9, 11, 23, 24]

To elucidate the influences of Ta⁵⁺ and In³⁺ co-doped TiO₂ structure in the sample on the potential dielectric mechanism. In Fig. 3, the XPS spectra of the ITTO ceramics were used to analyze the origin of CP, and different elements In, Ta, Ti, O were identified to the binding energies in the sample. Fig. 3(a) exhibited the binding energies (230.02 eV, 241.59 eV) of two peaks which confirmed the existence of Ta⁵⁺ [25]. Meanwhile, the binding energies (444.51 eV, 452.07 eV) of two peaks were assigned with the presence of In³⁺ in Fig. 3(b) [26].

(1)

Figure 3(c) exhibited the three energy peaks components of O1s profile, which can be confirmed as the bulk Ti-O bond (530.12 eV), oxygen vacancies (531.5 eV), and the surface hydroxyl (OH) (532.52 eV), respectively [27]. Another for Ti2p, two different peaks (458.79 eV, 464.63 eV) could be found in Figure 3(d), which can be suggested to the Ti⁴⁺ ion. Moreover, two small peaks indicate the existence of Ti³⁺ with lower binding energy of 459.5 eV and 463.86 eV [28]. Based on the pure rutile TiO₂, the adulteration of In³⁺ ion can form oxygen vacancies for charge compensation. While the Ta element instead of the Ti element, some extra electrons are generated, transforming Ti⁴⁺ ions to Ti³⁺ ions, as follows:

(2)

Ti4⁺+ e → Ti³⁺ (3)

The \({\text{V}}_{\text{O}}^{{\bullet }{\bullet }}\) is the oxygen vacancy, the \(\text{T}{\text{a}}_{\text{Ti}}^{{\bullet }}\) represents Ta on the Ti lattice site, and the \(\text{I}{n}_{\text{Ti}}^{\text{'}}\) represents in on the Ti lattice site.

As discussed above, doping Ta⁵⁺ ions which create extra free electrons have a positive effect on transforming Ti⁴⁺ ions to Ti³⁺ ions, especially sintering in the N₂ reducing atmosphere, the result of ultrahigh permittivity is obtained. Combining with In³⁺ ions, which are introduced to facilitate oxygen vacancies forming, keeping an electric neutrality of the system and forming different complex cluster-defects, including \({\text{I}\text{n}}_{2}^{3+}{\text{V}}_{\text{O}}^{{\bullet }{\bullet }}{\text{T}\text{i}}^{3+}\), \({\text{T}\text{a}}_{2}^{5+}{\text{T}\text{i}}^{3+}{A}_{\text{T}\text{i}} (A= {\text{I}\text{n}}^{3+}, {\text{T}\text{i}}^{4+}, {\text{T}\text{i}}^{3+})\) and so on. The moving of electrons is limited because of the various defect dipole clusters, further obtaining ultralow dielectric loss, the result is consistent with Fig. 2(a). Further in high temperature ranges, the result of ultrahigh permittivity could be related to the defect clusters are polarized. Although most of the defect clusters could not be activated at the lower temperature ranges, the localizable electrons could be polarized as well as move in a short distance, achieving an ultrahigh permittivity. As a result, the excellent dielectric properties and temperature stability should be closely connected to the localization of various complex cluster-defects, which could be originated from the EPDD.

In summary, the ITTO ceramics with dense microstructure and exceptional dielectric properties were achieved by a solid-state reaction process with N₂ reducing atmosphere. At 1 kHz, it is worth promoting the ultrahigh permittivity (ε_r = 1.18×10⁵) and ultralow dielectric loss (tanδ = 0.0072) in microelectronic devices. Emphatically, the temperature coefficient of the sample is calculated at 1 kHz, which has potential applications in X9D (-100°C - 235°C, Δε_r/ε_25°C < ± 3%) capacitor, and the excellent dielectric performances could be attributed to the EPDD. As an applicability, the excellent high temperature range above 200°C has potential requirement for the engine compartment of new energy vehicles.

Acknowledgements

The present work was supported by the National Natural Science Foundation of China (51572160), the National Key Research and Development Program of Shaanxi Province (Grant 2021GY-224), and Graduate Innovation Fund of Shaanxi University of Science and Technology.

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Ultrahigh Permittivity, Ultralow Loss and Stability in (In_0.5Ta_0.5)_0.1Ti_0.9O₂ Ceramics With Temperature Range From -100 to 235 °C

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