Thermal Expansion and High-Temperature Phase Transition of Ba6−3xLn8+2xTi18O54 (Ln=La, Nd, and Sm) Ceramics |
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Authors: | Ni Qin Xiao Qiang Liu Xiang Ming Chen |
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Affiliation: | Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China |
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Abstract: | Thermal expansion behaviors of Ba6?3 x Ln8+2 x Ti18O54 (Ln=La, Nd, and Sm, x =0.5, 0.67, and 0.75) ceramics were determined by dilatometric measurement. The samples of all investigated compositions expanded nearly linearly with increasing temperature in the range of 20°–1200°C. Their thermal expansion coefficients were determined to be 10.7–11.4 ppm/°C. A discontinuous change in sample size was observed at about 1350°C for each composition, indicating the existence of a phase transition. As determined by the high-resolution X-ray diffraction analysis, the phase constitution and the lattice parameters of Ba6?3 x Sm8+2 x Ti18O54 ceramics were maintained in the quenched samples. The origin of the phase transition was discussed thoroughly. Phase equilibrium in the BaTiO3–Ln2/3TiO3 system was reviewed by considering the phase transition. |
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