Ferroelectric Phase Transition in Cu-doped BaTiO3 Crystals

Abstract

The paper examines the ferroelectric-paraelectric phase transition in Cu:BaTiO 3 single crystals. Using thermo-currents and dielectric measurements, we found for pure samples the phase transition temperature to be close to Curie temperature (T c =120°C) with an anisotropy of the dielectric constantε.The lowering of temperature T m , corresponding to the maximum of pyroelectric signal, with the increase of concentration of impurities is confirmed by measurements of ε. Moreover, the ε(T) curves show progressive broadening as well as higher peak with the increase of impurity concentration, and the transition becomes more and more diffuse. The same effect occurs when the samples are subjected to a laser irradiation (λ=5145Ǻ). During annealing, crystals lose copper and T m is thereafter observed to increase again. BaTiO 3 is a displacive ferroelectric (having high permittivity k-values) which undergoes a first order phase transition. Ions substitutions have an effect on the lattice dynamics attributed to charge transfer to Ti and a lowering of elastic forces in BaTiO 3 .

Effect of some dopants on temperature of high-temperature phase transitions of Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free relaxor ferroelectrics ceramics seen via acoustic emission

“…We speculate that the acting of negative chemical pressure overbalances the acting of heavier Ta 5+ ion mass in comparison with Ti 4+ ion mass and drives both T m and T p up through P 4bm to P 4/mbm to Pm3m phases. So, our data has unambiguously established that both T m and T p linearly shift by a rule: the heavier the mass of the incorporated ions, the lower both T m and T p , and vice versa, in accordance with that established for the T c in perovskite displacive FEs [25][26][27][28][29][30][31][32][33][34][35][36], possessing the soft mode [25,[37][38][39]. This is no wonder because both the corresponding phase transitions are caused by softening of the R 25 mode and the M 3 mode, respectively, characteristic for perovskite of displacive type, obeying the Curie-Weiss law, in NBT crystals [60].…”

“…For example, in BaTiO 3 the T c shifts up when substituting the Ba 2+ ion for its lighter isotope as well as when substituting the Ti 4+ ion for its lighter isotope, and the T c shifts linearly down when substituting the Ti 4+ ion for its heavier isotope [25]. When substituting the Ti 4+ ion for Cu 2+ [26,27] and Sn 4+ [26], and Mn 4+ [28], and Ce 4+ [29,30], and Nb 5+ [31], and Hf 4+ [32], and Cr 3+ [33] ions, the T c shifts linearly down in dependence of the amount of these dopants because the mass of each dopant is heavier in comparison with the mass of the Ti 4+ ion. On the other hand, when substituting the Ba 2+ ion for Bi 3+ , Li + ions, the T c shifts linearly up in dependence of the amount of these dopants, because the mass of the Li + ion is many times lighter in comparison with the mass of the Ba 2+ ion [34], and the T c shifts linearly down when substituting the Ba 2+ ion for a heavier La 3+ ion [33,35,36].…”

“…Both the dependences of T m (wt%) and T p (wt%) look as straight, approximately parallel lines, and both T m and T p decrease as the wt% of the incorporated ions increases. It is clear that Cu 2+ [26,27], Fe 3+ [56,57] and Sb 3+ [58] ions substitute the Ti 4+ ion in the B-site due to approximate equality of their radii (table 1), and when substituting the Ti 4+ ion for heavier Cu 2+ , Fe 3+ and Sb 3+ ions the T m shifts down linearly. It is clear, too, that La 3+ ion substitutes the heavier Bi 3+ ion [50] and the T m shifts up.…”

Modification of the ferromagnetic properties of Fe-doped BaTiO3 polycrystalline ceramics by using Bi3+ doping

“…Tetragonal BaTiO 3 , as a ferroelectric material with a transition temperature (T C ) of 120 • C, has a wide range of applications such as MLCC (multilayer ceramic capacitors), PTCRs (positive temperature coefficient of resistance thermistors) or piezoelectric sensors [1][2][3]. Recently, BaTiO 3 has been a popular candidate as a host material in the research on multiferroic materials [4].…”