Combustion synthesis and properties of ferroelectrics, relaxor ferroelectrics & microwave resonator materials

Abstract

Dielectric materials include ferroelectrics, relaxor ferroelectrics and microwave resonators which are classified on the basis of their dielectric performances like dielectric constant, dielectric loss and piezoelectric coefficient. Present investigations are aimed at synthesizing ferroelectric, relaxor ferroelectric and microwave oxide materials by a novel low-temperature initiated, self-propagating, gas-producing, exothermic reactions. Combustion-synthesized oxide materials have been characterized using powder X-ray diffraction analysis. The fine particle nature has been studied using density, surface area and particle size analysis, and electron microscopy (SEM and TEM). Dielectric properties such as capacitance, dielectric loss, piezoelectric coefficient (d33) and polarization have also been studied. Combustion synthesis of (i) ferroelectric oxides, alkaline earth titanates, MTiO? and zirconates, MZrO? where M = Ca, Sr and Ba, and lead-based perovskites PbTiO?, PbZrO?, Pb(ZrxTi???)O? and Pb?.??La?.??(Zr?.??Ti?.??)?.??O?, (ii) relaxor ferroelectric oxides Pb(B?B?)O?, where B? = Fe, Ni, Zn and Mg; B? = Nb and their solid solutions with PbTiO? and BaTiO? and (iii) microwave resonators such as Ln?Ti?O? [Ln = La, Nd and Sm] and M?Nb?O? [M = Ca and Sr] has been described. The alkaline earth titanates and zirconates have been prepared by the pyrolysis of metal titanyl/zirconyl oxalates using ammonium nitrate as an oxidizer and oxalyl dihydrazide (ODH) fuel. They have also been prepared by the combustion of redox mixture comprising of metal nitrates, titanyl nitrate/zirconium nitrate and tetraformal trisazine (TFTA). The particulate and dielectric properties of pyrolysis-derived powders have been compared with that of combustion-derived powders. Similarly, the lead-based perovskites have been prepared by the combustion of metal hydrazinecarboxylate precursors and redox mixtures containing metal nitrates and TFTA. Both relaxors and microwave resonators have been prepared by the combustion of corresponding metal nitrates (M = Pb, La, Nd and Sm, Ti, Fe, Ni, Zn, Mg), niobium oxalate with ammonium nitrate and TFTA at 350°C. Single-phase products such as Pb(Mg?/?Nb?/?)O?, Pb(Fe?/?Nb?/?)O? and Pb(Ni?/?Nb?/?)O? [except Pb(Zn?/?Nb?/?)O?] are formed when calcined at 800°C. Perovskite phase of lead zinc niobate was stabilized with BaTiO? and PbTiO? near the morphotropic phase boundary. Relaxor compounds are sinteractive and achieve 95–98% theoretical density when sintered at 1050°C for 2 hours. As-prepared powders are all single-phase with large surface area of 10–29 m²/g. The powders are sinteractive and achieved 90–97% theoretical density when sintered at 1300°C for 1 hour. The sintered microwave resonator materials showed dielectric constant (30–40) with high quality factor (of the order of 1000).