Ultrahigh Permittivity , Ultralow Loss and Stability in ( In 0 . 5 Ta 0 . 5 ) 0 . 1 Ti 0 . 9 O 2 Ceramics With Temperature Range From-100 to 235 ° C

Ying Xue Shaanxi University of Science and Technology Xi'an Campus: Shaanxi University of Science and Technology Zhuo Wang (  wangzhuo@sust.edu.cn ) Shaanxi University of Science & Technology Yanxin Li Shaanxi University of Science and Technology Xi'an Campus: Shaanxi University of Science and Technology Zhihui Yi Shaanxi University of Science and Technology Xi'an Campus: Shaanxi University of Science and Technology Xin Li Shaanxi University of Science and Technology Xi'an Campus: Shaanxi University of Science and Technology Dan Wu Shaanxi University of Science and Technology Xi'an Campus: Shaanxi University of Science and Technology


Introduction
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 di cult to develop applicable properties of dielectric materials for such applications. Understanding historical research, plenty of colossal permittivity (CP) materials were synthesized, including the BaTiO 3 ceramics and ACu 3 Ti 4 O 12 (A = Ca, Sr, Bi, Na, Cd) materials [1][2][3][4]. Although BaTiO 3 has been reported with excellent dielectric properties, the permittivity of pure BaTiO 3 near Tc which was 120°C uctuates massively.
It is worth noting that (In 0.5 Nb 0.5 ) x Ti 1−x O 2 ceramics were prepared by Liu et al. using a solid-state method in 2013 [10], and the systems exhibited CP (ԑ r > 2 × 10 4 ) and low dielectric loss (tanδ < 0.05), simultaneously showed good frequency and temperature stability over wide ranges. Li et al. reported the (La 0.5 Nb 0.5 ) x Ti 1−x O 2 samples with dielectric loss (tanδ = 0.02896) and permittivity (ε r = 49692), but the samples only ful lled temperature stability for X8R [11]. Peng  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 0.5 Ta 0.5 ) x Ti 1−x O 2 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 TiO 2 -based ceramics [14][15][16][17][18][19][20][21], but these reported materials which were di cult to balance permittivity, dielectric loss and temperature stability, especially further satisfy the requirements for high temperature industrial application above 150°C.
Compared with Nb 5+ ion, Ta 5+ 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 N 2 reducing atmosphere. In this work, the In 3+ and Ta 5+ co-doped TiO 2 ceramics based on the solid-state reaction method were synthesized in N 2 reducing atmosphere. The excellent dielectric properties with ultrahigh permittivity (1.18 × 10 5 at 1 kHz), ultralow dielectric loss (0.0072 at 1 kHz) and temperature stability which satis es X9D (-100°C -235°C, Δε r /ε 25°C < ± 3.3%) were exhibited.

Experimental Details
The (In 0.5 Ta 0.5 ) 0.1 Ti 0.9 O 2 (abbreviated by ITTO) ceramics were synthesized using a solid-state reaction process. The prepared materials of TiO 2 (99.99%, rutile, Aladdin), In 2 O 3 (99.99%, Aladdin), and Ta 2 O 5 (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 N 2 reducing atmosphere.
The phase structure was executed using Raman spectroscopy (Renishaw-invia) and X-ray diffraction (XRD) technique (D8 advance, Germany), and the Rietveld re nement result was tted 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 tted 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 TiO 2 crystal structure [16]. In terms of the Rietveld re nement, 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 re nement are larger than ( a = b = 4.593, c = 2.959 (JCPDS 21-1276)) for pure rutile TiO 2 [22]. As a result, the lattice size of the increase could be related to the Ta 5+ and In 3+ of larger ionic radii instead of the Ti 4+ ions, indicating Ta 5+ and In 3+ form a complete solid solution in rutile TiO 2 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.

Results And Discussion
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 1.18×10 5 at 1 kHz, respectively, including the good frequency and temperature stability. Meanwhile, Fig. 2(b) exhibited the temperature function of ITTO ceramics. The temperature coe cient of the sample is calculated between ± 3.3% at 1 kHz, which satis es X9D (-100°C -235°C, Δε r /ε 25°C < ± 3.3%), and Fig. 2(c) exhibited between ± 4.7% at 10 kHz, which satis es 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 in uences of Ta 5+ and In 3+ co-doped TiO 2 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 identi ed to the binding energies in the sample. Fig. 3(a) exhibited the binding energies (230.02 eV, 241.59 eV) of two peaks which con rmed the existence of Ta 5+ [25]. Meanwhile, the binding energies (444.51 eV, 452.07 eV) of two peaks were assigned with the presence of In 3+ in Fig. 3(b) [26].
(1) Figure 3(c) exhibited the three energy peaks components of O1s pro le, which can be con rmed 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  Ti 3 + A Ti (A = In 3 + , Ti 4 + , Ti 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.

Conclusions
In summary, the ITTO ceramics with dense microstructure and exceptional dielectric properties were achieved by a solid-state reaction process with N 2 reducing atmosphere. At 1 kHz, it is worth promoting the ultrahigh permittivity (ε r = 1.18×10 5 ) and ultralow dielectric loss (tanδ = 0.0072) in microelectronic devices. Emphatically, the temperature coe cient 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.