Diffuse Phase Transition in Sr₅RTi₃Nb₇O₃₀ (R = La, Nd, Sm, Gd and Dy) Ferroelectric Ceramics

Some compounds with a general formula Sr ₅ RTi ₃ Nb ₇ O ₃₀ (R = rare-earth ions), which belong to tungsten-bronze structural family were prepared using a high-temperature solid-state reaction technique. X-ray diffraction (XRD) study confirms the formation of the compounds in an orthorhombic phase at room temperature. Real part of the complex permittivity (ϵ ′) and dissipation factor (tanδ) of the samples has been measured as a function of frequency at different temperature. All the compounds except La-based show the dielectric anomaly and phase transition above the room temperature. Detailed impedance spectroscopic study provides electrical conduction and relaxation behavior of the materials. Measurement of conductivity as a function of temperature suggests that the samples have negative temperature coefficient of resistance (NTCR) with a typical semiconductor behavior.

Keywords:

• Ferroelectrics
• ceramic
• tungsten-bronze structure
• impedance spectroscopy

Acknowledgments

Paper originally presented at AMF-4, Bangalore, India, December 12-15, 2003