Phase transition and PTCR effect in erbium doped BT ceramics

Abstract

a b s t r a c tIn this work the dielectric behaviour and main features of the phase transition of BaTiO 3 and Ba 0.99 Er 0.01 TiO 3 ceramics were carefully investigated. The temperature and frequency dependences of the dielectric properties of erbium doped BaTiO 3 ceramics were measured in the 25-225 • C and 100 Hz to 10 MHz ranges, respectively. From this study, a dielectric anomaly in the ferroelectric-paraelectric phase transition of the Ba 0.99 Er 0.01 TiO 3 ceramic was observed. The features of the samples phase transition were analysed by using Curie-Weiss, Santos-Eiras' and order parameter local phenomenological models. In the BaTiO 3 system, all models showed a normal phase transition, while was not possible to establish the character of the phase transition in the Ba 0.99 Er 0.01 TiO 3 system. The relaxation parameters of conductive processes for the study ferroelectric materials, analysed in the time domain, did not show any influence on the ferroelectric-paraelectric phase transition. Finally, it was demonstrated that the anomaly observed on the phase transition of the erbium doped BaTiO 3 ceramics is associated with the processes that results in the PTCR effect.

Can erbium dopant occupy both cation sites in cubic barium titanate via a mechanism different than self‐compensation?

“…This parameter varies between 0.68 and 0.90, suggesting that the charge carriers move almost independently on their environment in this temperature range . Contrarily to previously reported results for undoped BT and for 1 mol% Er‐BT in the temperature range 313 K–513 K , β is found to increase with temperature.…”

“…The polymeric precursor method was used to process 1 mol% Er‐BT; details of the experimental conditions can be found elsewhere . The dielectric characterization of the material was carried out by Impedance Spectroscopy (IS) using a HP‐4194 spectrometer at temperatures between 298 and 973 K, at intervals of 10 K, and frequencies between 20 and 10 MHz.…”

“…One of the most outstanding features of Er‐doped and pure BT is the presence of a diffuse dielectric anomaly in the range 700–1000 K, above the Curie temperature ( T C ) , in the cubic paraelectric phase. The origin of this anomaly seems to lie in the existence of oxygen vacancies , which have been invoked to explain the ionic conductivity exhibited by this material. These are the only defects with considerable mobility in this system, since it has been demonstrated that the formation of electron–hole pairs as charge‐compensating agents is minority compared to that of oxygen vacancies , and that cation ones are by far less mobile .…”

“…Besides, Er‐BT presents a positive temperature dependence of the resistivity (PTCR effect) near the Curie temperature. Some models have been developed to explain the increment of the resistivity up to T C but none of them explains the conducting behavior, characteristic of oxygen vacancies .…”

Dielectric and microstructural properties of BaTiO3 and Ba0.9925Er0.0075TiO3 ceramics

“…al. [5] 2 and Er 2 O 3 were weighed using A&D Weighing HR250AZ pharma balance. Powder samples were mixed and ground using pestle and mortar.…”