Dense (97-99% relative 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 has been determined from the Rietveld refinement of high-energy X-ray diffraction data collected at ESRF. The pair distribution function analysis has been used to investigate the local structure and the level of disorder. The phase transitions and the evolution of polar order with composition have been 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 data provide a detailed picture of the BaCexTi1-xO3 system and a tentative composition-temperature phase diagram will be proposed. The results indicate that the three transitions (rhombohedral/orthorhombic, orthorhombic/tetragonal and tetragonal/cubic) typical of BaTiO3 (x = 0) meet at a critical point located at x » 0.10 and T = 115 °C. Evolution of the polar order from conventional ferroelectric to diffuse phase transition behavior and to relaxor state is observed with increasing x. Relaxor behavior is found at x >= 0.20. In contrast to 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 originated from the much larger ionic radius of Ce4+ (0.87 Å) in comparison to Ti4+ (0.605 Å).
Ferroelectric to relaxor crossover in the BaTiO3-BaCeO3 system
Canu G;Buscaglia MT;Buscaglia V
2017
Abstract
Dense (97-99% relative 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 has been determined from the Rietveld refinement of high-energy X-ray diffraction data collected at ESRF. The pair distribution function analysis has been used to investigate the local structure and the level of disorder. The phase transitions and the evolution of polar order with composition have been 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 data provide a detailed picture of the BaCexTi1-xO3 system and a tentative composition-temperature phase diagram will be proposed. The results indicate that the three transitions (rhombohedral/orthorhombic, orthorhombic/tetragonal and tetragonal/cubic) typical of BaTiO3 (x = 0) meet at a critical point located at x » 0.10 and T = 115 °C. Evolution of the polar order from conventional ferroelectric to diffuse phase transition behavior and to relaxor state is observed with increasing x. Relaxor behavior is found at x >= 0.20. In contrast to 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 originated from the much larger ionic radius of Ce4+ (0.87 Å) in comparison to Ti4+ (0.605 Å).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
