Dielectric Properties and the Phase Transition of Pure and Cerium Doped Calcium-Barium-Niobate

Abstract

The complex dielectric constant of pure and cerium doped calcium-barium-niobate (CBN) was studied at frequencies 20 Hz ≤ f ≤ 1 MHz in the temperature range 300 K ≤ T ≤ 650 K and compared with the results for the well known ferroelectric relaxor strontium-barium-niobate (SBN). By the analysis of the systematically taken temperature and frequency dependent measurements of the dielectric constant the phase transition characteristic of the investigated materials was evaluated. From the results it must be assumed that CBN shows a slightly diffuse phase transition without relaxor behavior. Doping with cerium yields a definitely different phase transition characteristic with some indications for a relaxor type ferroelectric material, which are common from SBN

Investigations on Fe doped Ba0.95Sr0.05TiO3 single phase magnetodielectric compounds

“…From the fig. it is seen that the e passes through a diffused phase transition (DPT) at T c and the T c decreases with increasing Fe concentration [21]. The diffused phase transition in the e versus T behaviour may occur because of the micro-chemical inhomogeneity induced by the substitution of Fe at very low concentration i.e.…”

Investigations on Fe-doped strontium barium niobate, single phase ferroelectric and magnetodielectric compounds

“…For between 1 and 2, the phase transition is partially diffused and the corresponding materials are termed as partial relaxors. 19 Therefore, essentially SBN50 and SBN40 show a partial relaxor behavior. Figures 5(a) and 5(b) show the variation of " as function of temperature T at frequencies 1 kHz, 10 kHz, 100 kHz and 1 MHz for SBNFe02 and SBNFe05, respectively.…”

“…19 From Figs. 4(a) and 4(b), it is observed that log (1/" À 1/" max ) versus log (T À T m ) shows a linear behavior for temperatures from 8 to 20 K, above T m .…”

Critical slowing down and elastic anomaly of uniaxial ferroelectricCa0.28Ba0.72Nb2O6crystals with tungsten bronze structure

“…In a previous study, it has been shown that CBN28 and SBN61 have a similar unit-cell size [13,28]. On the other hand, the Ca 2+ ion radius is 1/ s [21]. Thus the lower disorder of the Ca 2+ and Ba 2+ ions is the origin of the weak random fields in CBN28, which prefers a longerrange order and causes the weakly first-order phase transition of the order-disorder type with a sharp critical slowing down in the vicinity of T C .…”

“…Other consequences of the weaker diffusive nature are the decrease in the index of the extended Curie-Weiss law to 1.65 and the lack of a frequency-dependent high-T shift in the susceptibility peak T m [21]. It was assumed that the outstanding characteristics of SBN are associated with the relatively small lattice parameters [13], whereas CBN actually has lattice parameters smaller than those of SBN.…”