High-temperature antiferroelectric and ferroelectric phase transitions in phase pure LaTaO4
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Universidade Federal de Minas Gerais
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Phase-pure LaTaO4 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 Cmc21 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 LaTaO4 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.
Abstract
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Cristais ferroeletricos, Material cerâmico, Espectros vibracionais, Dielétricos, Transformações de fase (Física estatística), Raman, Espectroscopia de
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Ferroelectrics, LaTaO4, Vibrational spectroscopy, Dielectrics, Phase transitions
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https://www.sciencedirect.com/science/article/pii/S0272884216318971