Structure-property relationships in BaCexTi1-xO3 (x = 0.02 - 0.30) ceramics

The incorporation of homovalent M4+ ions at the Ti site of BaTiO3 with formation of the BaMxTi1-xO3 solid solutions (M = Sn, Zr, Hf, Ce) determines significant modifications of the phase transitions, polar order and functional properties. These materials are attractive for applications such as high energy density capacitors, tunable microwave dielectrics and electrocaloric effect-based cooling devices [1-3]. Unlike the systems containing Sn and Zr, the impact of structural disorder and local structure on the evolution of polar order and properties in Ce-doped barium titanate ceramics has not been investigated in detail yet. Dense (97-99% rel. density) ceramic samples with composition BaCexTi1-xO3 (x = 0.02, 0.05, 0.06, 0.10, 0.12, 0.15, 0.175, 0.20 and 0.30) were prepared by the conventional solid-state route starting from fine precursor powders and sintered at 1450-1500 °C. The average crystal structure at different temperatures in the range 100-400 K was determined from the Rietveld refinement of high-energy X-ray diffraction data collected at ESRF. The pair distribution function analysis was used to investigate the local structure and the level of disorder. The phase transitions and the evolution of polar order with composition were studied using dielectric permittivity measurements at 100 Hz-1 MHz between -150 and 150 °C, variable temperature Raman spectroscopy (from -195 to 165 °C) and differential scanning calorimetry (-100 - 150 °C). The ferroelectric hysteresis loops were measured at room temperature. Overall, the data provide a detailed picture of the BaCexTi1-xO3 system and a composition-temperature phase diagram will be proposed. A polar local structure exists irrespective of the long-range average symmetry for all compositions. Differently from the homologous systems BaSnxTi1-xO3 and BaZrxTi1-xO3, a diffuse ferro/para transition is already observed at x = 0.05 as a consequence of the high level of lattice disorder while relaxor behaviour occurs when x >= 0.20. References [1] V. V. Shvartsman, D. C. Lupascu, J. Am. Ceram. Soc., 95, 1-26 (2012) [2] X. S. Qian et al., Adv. Funct. Mater., 24, 1300-1305 (2014) [3] V. Buscaglia et al., J. Phys: Condens. Matter, 26, 065901 (2014)