Investigation on Electrical Properties and Microdefects of Nb5+-Doped BaTiO3 Based Ceramics by Positron Annihilation Techniques

Xuxin Cheng,Xiaoming Chen,Yuxin Wang,Haining Cui

doi:10.1590/1980-5373-mr-2018-0921

Abstract

The influence of the Nb5+-doped content and the doping CaCO3 on the electrical properties and the microdefects of BSTN ceramics by Positron Annihilation Techniques were studied, which were fired at 1350 oC for 2 hours in air. The PTCR characteristics in the BSTN samples were also investigated. Moreover, the information on microdefects in BSTN ceramics was demonstrated by coincidence Doppler broadening spectrum measurements and positron annihilation lifetime spectra. Meanwhile, the influence of the defects on the electrical properties of the ceramics was also revealed. Furthermore, the critical donor-dopant content was 0.4 mol%, which corresponding room-temperature resistivity and the resistivity jumping ratio was 714.3 Ω·cm and 2.77 × 102, respectively. In addition, the average positrons annihilate lifetime t of the BSTN ceramics was investigated as well.

Highlights

Barium titanate is a ferroelectric material, which transforms from a tetragonal perovskite structure (ABO3) into a paraelectric structure 1
Deng et al 8 suggested that the Nb addition was effective in enhancing the d–d interactions by Positron Annihilation Techniques (PAT)
The average grain sizes of the samples doped Ca2+ of 0–8 mol% are 6.88 μm, 4.47 μm, and 2.80 μm, respectively. It indicates that the grain size of the specimens decreases quickly with an increase of the concentration of CaCO3; the grain size of the SP6 samples becomes very uniform in Fig.[1] (c), probably due to the inhibition of the grain growth with an increase in the CaCO3 content

Summary

Introduction

Barium titanate is a ferroelectric material, which transforms from a tetragonal perovskite structure (ABO3) into a paraelectric structure 1. Heywang 4 explained this phenomenon, and an improved discussion was later provided by Jonker 5.The PTCR characteristic of doped BaTiO3 ceramics is considered to a grain-boundary effect. An effective method is considered to detect defects in bulk by positron annihilation technology (PAT) 6, 7, which include the coincidence Doppler broadening spectrum (CDBS) and positron annihilation lifetime spectra (PALS). The momentum distribution of the annihilating e+–e′ pairs can be detected using the CDBS; the annihilation information of positrons can be offered by the PALS. Deng et al 8 suggested that the Nb addition was effective in enhancing the d–d interactions by Positron Annihilation Techniques (PAT). A high amount of titanium vacancies could lead to grain-growth inhibition 11. The charge compensation was achieved by titanium vacancies and electrons 13

Objectives

Results

Conclusion