Structural, dielectric and impedance spectroscopy analysis of Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ferroelectric ceramic

Abstract

In this work, Zn co-doped tungsten bronze having nominal formula Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ has been synthesized and systematically studied for structure, dielectric and electrical properties. The formation of the phase of tetragonal tungsten bronze with space group <i>P</i>4<i>bm</i> and the occurrence of oxygen vacancies were verified by the Rietveld refinement using X-ray diffraction data. Scanning electron microscopy (SEM) of Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ ceramic shows high densification, low porosity, and homogeneous distribution of grains of different sizes over the total surface. The sample shows a dielectric anomaly of ferroelectric paraelectric type at 262 °C, and has non-relaxor type of diffuse phase transition. The electrical property (complex impedance <i>Z</i>*, complex permittivity <i>ε</i>*, complex modulus <i>M</i>*) of Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ ceramic has been investigated by non-destructive complex impedance spectroscopy (CIS) as a function of frequency at different temperatures. Grains and grain boundaries conduction is detected from a complex impedance spectrum by fitting the Nyquist plot with an appropriate electrical circuit. The Nyquist plot indicates the negative temperature coefficient of resistance (NTCR) character of Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ ceramic. The variation of AC conductivity as a function of frequency reveals that the compound has an Arrhenius-type behavior of electrical conductivity. The DC electrical conductivities of grains and grain boundaries have been studied. The presence of non-Debye relaxations was verified by a complex modulus analysis.