Structural, dielectric and impedance spectroscopy analysis of Ba₅CaTi_1.94Zn_0.06Nb₈O₃₀ ferroelectric ceramic

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 P4bm 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 Z*, complex permittivity ε*, complex modulus M*) 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.