Dielectric properties and microstructural behaviour of B-site calcium-doped barium titanate ceramics

Effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6−xCaxTiO3 (0⩽x⩽0.3) perovskites

“…What is unexpected is that a shows an anomalous expansion in the Ca doping region of 0.15Ͻ x ഛ 0.18. We note that previous experimental results including the equilibrium electric conductivity, 6 neutron diffraction, 8 Raman and dielectric spectroscopies, 9,[21][22][23] scanning electron microscopy, 9 and atomic location by channel-enhanced microanalysis 7 ͑ALCHEMI͒ have given evidences that a small amount of Ca ions can substitute for Ti ions in the Ba 1−x Ca x TiO 3 , Ba 1−x Sr x Ti 1−y Ca y O 3−y , and Ba͑Ti 1−x Ca x ͒O 3−x series, although the ionic radius and chemical valence of the Ca ion differ much from those of the Ti ion. A possibility for this anomaly may be associated with the tilting of the oxygen octahedra, which commonly occurs in perovskites.…”

Aging-induced double hysteresis loops in bismuth-doped (Ba,Ca)TiO3 ferroelectric ceramics

“…For Bi-doped BCT with the ABO 3 perovskite structure [(Ba 0.90 Ca 0.10 ) 0.925 Bi 0.05 TiO 3 ], there are two possible vacancies: first, the Bi 3+ ions substituted for A-site divalent ions (Ba 2+ or/and Ca 2+ ) in BCT can be located at off-center positions of the A site, so that A-site vacancies are formed to compensate for the charge imbalance arising from the substitution, and second, the Ca 2+ ions substitute for Ti 4+ ions in BCT and cause the formation of O 2À vacancies to balance the charge misfit. The previous experimental results from equilibrium electric conductivity, 14 scanning electric microscopy, 15 neutron diffraction, 16 and Raman and dielectric spectroscopies, 15,17,18 have given evidence that a small amount of Ca 2+ ions can substitute for Ti 4+ ion, causing the formation of O 2À vacancies to balance the charge misfit, although the ionic radius and chemical valence of the Ca 2+ ions is different from those of the Ti 4+ ions. Krishna et al 16 found that 4 mol% Ca 2+ ions had substituted for the Ti 4+ ions even when the molar ratio of (Ba + Ca)/Ti was 1 for the starting materials used in their studies of Ba 0.88 Ca 0.12 TiO 3 samples prepared by the solid-state reaction technique.…”

“…However, until now, there has been no direct indication of the appearance of antiferroelectric components in (Ba,Ca)TiO 3 . [13][14][15][16][17][18] Besides, the double P-E loops observed in (Na,Bi)TiO 3 -based ceramics [6][7][8] are at temperatures near T c , while those reported in aged BaTiO 3 /(Ba,Sr)TiO 3 , 9,10 KNbO 3 , 11 and BiFeO 3 12 are far below T c . These give essential evidence that aging may induce double P-E loops in (Ba,Ca)TiO 3 at room temperature.…”

Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds

“…Figure 5 shows the T C as a function of in a large number of Ba 1-x-y Sr x Ca y TiO 3 with the tolerance factor greater than 1 reported in the literature over the last 60 years12204041424344454647484950515253545556575859. A strong linear correlation is observed with some scatter of data presumably due to compositional inhomogeneity (including partial substitution of Ca on B site52), annealing conditions5, thermal hysteresis during the measurements43, etc.…”