High-temperature antiferroelectric and ferroelectric phase transitions in phase pure LaTaO<sub>4sub>
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- 作者：Yuslí ; n G. Abreu<sup>asup><sup> ; sup><sup>bsup> ; Kisla P.F. Siqueira<sup>asup> ; Franklin M. Matinaga<sup>csup> ; Roberto L. Moreira<sup>csup> ; Anderson Dias<sup>asup><sup> ; sup><sup>anderson_dias@iceb.ufop.br" class="auth_mail" title="E-mail the corresponding authorsup>
- 关键词：Ferroelectrics ; LaTaO4 ; Vibrational spectroscopy ; Dielectrics ; Phase transitions
- 刊名：Ceramics International
- 出版年：2017
- 出版时间：January 2017
- 年：2017
- 卷：43
- 期：1
- 页码：1543-1551
- 全文大小：1196 K
文摘
Phase-pure LaTaO<sub>4sub> ceramics was prepared by solid-state reaction. Dielectric spectroscopic data as well as differential scanning calorimetric experiments showed the existence of a sequence two high-temperature first-order structural phase transitions. The first phase transition occurs above 160 °C (on heating), from the monoclinic P21/c space group at room temperature to the polar orthorhombic Cmc2<sub>1sub> group, exhibiting a very large thermal hysteresis probably linked to the reconstructive nature of the structural transition. The second transition occurs around 225 °C to the orthorhombic Cmcm space group, with a small thermal hysteresis. Vibrational Raman spectroscopic analyses confirmed these two sequential phase transitions, as well as the thermal hysteresis observed for both first-order transitions in repeated heating and cooling cycles. The existence of a strong monoclinic distortion at room temperature could be related to the presence of defects (oxygen vacancies) in LaTaO<sub>4sub> ceramics, after sintering. Dielectric spectroscopy showed a strong influence of the electric conductivity on the dielectric response with activation energy of dc component of conductivity (0.62 eV) compatible with the presence of oxygen vacancies. Far-infrared data confirmed that the extra modes observed in the Raman spectra are forbidden bands, which were activated by defects into the structure.