Phase transition and conduction mechanism in Pb2Na0.8R0.2Nb4.8Fe0.2O15 material (R=rare earth)

• We found that TB compounds exhibit a diffuse type of first- order transition.
• A negative temperature coefficient of resistance (NTCR) behaviour is observed.
• Three conduction mechanisms were identified: n-and/or p-type at low temperatures.
• The conduction mechanism in the studied compounds is very complex.

Electrical properties of Pb2Na0.8Eu0.2Nb4.8Fe0.2O15 tungsten bronze compound were investigated. Ferroelectric phase transition of diffuse type is observed at 395 °C. Conductivity study as a function of temperature (RT-600 °C) and at three different frequencies (10, 100 and 1000 kHz) suggests the existence of dominant ionic conduction. The rise of ac conductivity on increasing temperature supports the NTCR (negative temperature coefficient of resistance) behaviour of the material. The activation energies have been evaluated from ac conductivity using Arrhenius equation and discussed. Different conduction mechanisms were identified. For comparison, the conducting properties of Pb2Na0.8R0.2Nb4.8Fe0.2O15 (R=Dy, Nd, La) were also investigated.

Thermal evolution of lnσac of Pb2Na0.8Eu0.2Nb4.8Fe0.2O15 at selected frequencies.Figure optionsDownload as PowerPoint slide