Dielectric Properties of Rhombohedral

Dielectric materials are needed in many electrical and electronic applications. So, basic characterizations need to be done for all dielectrics. (PN) is ferroelectric and piezoelectric only in its orthorhombic phase, with potential high temperature applications. So, its rhombohedral phase, frequently formed as an undesirable impurity in the preparation of orthorhombic PN, has been ignored with respect to possible dielectric characterizations. Here, essentially single phase rhombohedral PN has been prepared, checking structure from XRD Rietveld Analysis, and the real and imaginary parts of permittivity measured in an Impedance Spectrometer (IS) up to ~ and over 20？Hz to 5.5？MHz range, for heating and some cooling runs. Variations, with temperature, of relaxation time constant ( ), AC and DC conductivity, bulk resistance, activation energy and capacitance have been explored from our IS data. 1. Introduction Commercial piezoelectric (PE) materials for applications in medicine, industry, and research have mostly been barium titanate (BaTiO3), lead zirconate titanate (Pb[ZrxTi1-x]O3, , or PZT), or materials based on one of these. But Curie temperature, the upper limit for piezoelectricity, is at best 130°C [1, 2] for the former and 390°C [2] for a specially modified PZT. Now, certain modern high temperature applications in industry need higher Curie temperature and, hence, newer materials with higher Curie temperature and suitable PE properties. This growing need for high temperature piezoelectric sensors and actuators [1, 2] has revived, in last few decades, a worldwide interest in lead niobate (PbNb2O6, to be shortened here as PN) in orthorhombic structure, which alone is piezoelectric. It was discovered [3] in 1953 but almost ignored for decades after a wave of pioneering work [3–5] of high quality. PN and PN-based ferroelectric samples involving chemical substitution &/or composite formation [6–8] are now being investigated by different groups, while present work is on pure PbNb2O6 in rhombohedral form. PbNb2O6 has different structures as already indicated. The stable forms of PbNb2O6 are [3–5, 9] rhombohedral (at low temperature) and tetragonal (at high temperature). The latter is transformed, usually by quenching ( ), to PNQ, the metastable orthorhombic PbNb2O6, which alone can be made piezoelectric (fortunately with a high Curie temperature higher than 580°C for 5.5？MHz, e.g., [9]). Slow ( ) cooling (from temperatures like 1270°C) leads [10, 11] to PNS, rhombohedral PbNb2O6, which is not ferroelectric; ruling out piezoelectric properties and