High-temperature antiferroelectric and ferroelectric phase transitions in phase pure LaTaO4. Issue 1 (January 2017)

• Record Type: Journal Article
• Authors: Abreu, Yuslín G.; Siqueira, Kisla P.F.; Matinaga, Franklin M.; Moreira, Roberto L.; Dias, Anderson
• Is Part Of: Ceramics international. Volume 43:Issue 1(2017)Part B
• Page Start: 1543
• Page End: 1551
• Publication Date: 2017-01
• Subjects: Ferroelectrics -- LaTaO4 -- Vibrational spectroscopy -- Dielectrics -- Phase transitions; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2016.10.128
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: 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 P 21/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. Graphical abstract: