Positron lifetime study in BaTiO₃ ceramics with different Ba/Ti ratios

Abstract

The positron lifetime spectra in 0.25 at.% La-doped BaTiO, with different Ba/Ti ratios have been measured at room temperature. It was found from the experiments that with deviating from exact stoichiometry the positron lifetime z2 decreases and the intensity I , increases for Ba/Ti ratio smaller than stoichiometric and they have more significantly similar changes for Ba/Ti ratio larger than stoichiometric. The non-monotonic dependence of positron lifetime parameters on Ba/Ti ratio is regarded as that the r2 component is contributed together by positrons annihilating at the grain boundaries and Ba vacancies and/or Ti vacancies, and small deviations from exact stoichiometry would be expected to increase the concentration of defects such as Ba vacancies for Ba/Ti < 1 and Ti vacancies for Ba/Ti > 1.

The Defects, Grain Size and Electrical Property in the Non-stoichiometric BaTiO3 Ceramics

“…Some investigations (DANIELS et al 1976, TSUDA et al1978TANG 1994a;TANG et al1995) have shown that the doping of trivalent ions such as La 3+ , Gd 3+ and Y 3+ for BaTiO 3 would induce production of Ba vacancies. Several works (COCKROFT et al 1991;TANG 1994b) have indicated that deviation of [Ba]/[Ti] ratio from 1 would be expected to increase the concentration of vacancy-type defects such as Ba-or Tivacancies. Thus when we discuss the defect variation by means of the positron lifetime parameters, the grain boundaries, Ba and Ti vacancies must be considered.…”

“…and small deviation in stoichiometry. Many subjects about them have been investigated by using X-ray diffraction (RUDDLESDEN et al1958), electron microscopy (HAANSTRA et al 1980), optical obsorption ), electron paramagnetic resonance (KUTTY et al 1985;KLEIN et al 1986;SCHWARTZ et al 1990;SCHWARTZ et al 1992;POSSENRIEDE et al 1992;SCHWARTZ et al 1993), laser spectroscopy (COCKROFT et al1991) and positron annihilation (TSUDA et al 1978;TANG 1994a;TANG 1994b;TANG et al 1995). These investigations took mainly aim at the influences of doping and preparation conditions.…”

Dependence of the Electric Properties and the Positron Lifetimes on the Dopant Content in La‐doped SrTiO3

“…It is important to study the structure and defects and their variations in order to understand the influence of variable causes on the properties of these materials. Many methods arid techniques such as X-ray diffraction (RUDDLESDEN, POPPER), electron microscopy (HAANSTRA, IHRIG) internal friction (GRIDNER, DARINSKII), electron paramagnetic resonance (KUTTY et al), laser spectroscopy (COCKROFT et al), positron annihilation (TSUDA et al, HE et al;TANG 1994aTANG , 1994bTANG , 1995 have been used to study structure and defects of perovskite materials. Among these methods and techniques the positron annihilation is an important and sensitive technique for the stiidy of vacancy type defects.…”