Name: Jaime Alberto Sanchez Caceres
Type: PhD thesis
Publication date: 12/12/2019
Advisor:

Namesort descending Role
Carlos Augusto Cardoso Passos Advisor *

Examining board:

Namesort descending Role
Adonias Ribeiro Franco Júnior External Examiner *
Carlos Augusto Cardoso Passos Advisor *
Estefano Aparecido Vieira External Examiner *
JOSE ALBINO OLIVEIRA DE AGUIAR External Examiner *
José Luis Passamai Junior External Examiner *
Marcos Tadeu DAzeredo Orlando Internal Examiner *

Summary: In this work, erbium-doped PZT 52/48 ceramics at sites A and B were prepared by the Pechini method for the purpose of studying their dielectric properties. Specifically, the dielectric anomalies of interfacial origin in these ferroelectrics were investigated. To determine the best sintering/densification temperature of our ceramic samples, dilatometry tests were performed. These results of the tests showed that the ceramic samples presented relative densities above 95%. The samples were analyzed by X-ray diffraction. The results indicated that all samples are single phase and the peaks are indexed to the tetragonal crystal structure. According to these results, there was also an increase of the parameter “a” and a reduction of the parameter “c” in relation to the undoped DZT sample. Through scanning electron microscopy, it was observed that average grain size decreased with increasing erbium content. All samples were subjected to electrical measurement analysis. The dielectric response of the grains showed characteristics of materials that follow Curie-Weiss law, typical of ferroelectrics. On the other hand, the dielectric anomaly phenomenon was observed for the responses of these materials at high temperatures and low frequencies. Impedance spectroscopy analyzes by equivalent circuit (brick-layer model) revealed a predominance of dielectric properties of intergranular interfaces as the cause of this anomaly. It was considered the layer model (grain and grain boundary) in series. The electrical characterization of our ceramics showed a peculiar ferroelectric-paraelectric phase transition around 390 °C. In addition, measurements of ferroelectric hysteresis for doped samples at sites A and B revealed that remnant polarization and coercive field values depend on erbium concentration and PbO losses. The undoped sample showed higher values of permittivity compared to erbium doped samples at both sites A and B.

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