Magnesium niobate

Kim et al. [208] synthesized perovskite-type Pb(Mgi/3Nb2/3)03 powders by an emulsion method with (a) an aqueous solution of lead nitrate, magnesium nitrate hexahydrate and niobium oxalate as the water phase, (b) Span 80 as the surfactant, (c) paraffin oil as an emulsifying agent and (d) kerosene as the oil phase. The emulsion of short stability, prepared by high speed mixing, was added drop by drop into petroleum heated at 170 C. The product particles were washed in toluene and cleaned at 150 C. Careful calcination yielded dominantly a pyrochlore phase at 600 C, but only the desired perovskite-type niobate at 800 C. 

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Because of very high dielectric constants k > 20, 000), lead-based relaxor ferroelectrics, Pb(B, B2)02, where B is typically a low valence cation and B2 is a high valence cation, have been iavestigated for multilayer capacitor appHcations. Relaxor ferroelectrics are dielectric materials that display frequency dependent dielectric constant versus temperature behavior near the Curie transition. Dielectric properties result from the compositional disorder ia the B and B2 cation distribution and the associated dipolar and ferroelectric polarization mechanisms. Close control of the processiag conditions is requited for property optimization. Capacitor compositions are often based on lead magnesium niobate (PMN), Pb(Mg2 3Nb2 3)02, and lead ziac niobate (PZN), Pb(Zn 3Nb2 3)03. 

Lead-lithium alloys, 14 779 Lead-lithium-tin alloys, 14 779 Lead magnesium niobate (PMN), 5 583 Lead manganese niobaterlead titanate (PMN PT), 22 713... 

Swartz, S.L. and Shrout, T.R. (1982) Fabrication of perovskite lead magnesium niobate, Mater. Res. Bull. 17, 1245-50. 

PMN-PT) are notorious for the difficulty to obtain as phase pure perovskite. To fabricate phase pure PMN it is necessary to prepare magnesium niobate (columbite) first, and then to heat a mixture of columbite with other oxide species. PbO is usually added in a small excess over exact stoichiometry that is a complicated and tedious process. 

The addition of various components to the lead magnesium niobate compositions was found to be advantageous for the dielectric properties. Addition of PbTiOs is commonly used to raise the Curie temperature of PMN composi-... 

Gallone G, Carpi F, De Rossi D, Levita G, Marchetti A (2007) Dielectric constant enhancement in a silicone elastomer filled with lead magnesium niobate-lead titanate. Mater Sci Eng C 27 110... 

Pyro- and Piezoelectric Properties The electric field application on a ferroelectric nanoceramic/polymer composite creates a macroscopic polarization in the sample, responsible for the piezo- and pyroelectricity of the composite. It is possible to induce ferroelectric behavior in an inert matrix [Huang et al., 2004] or to improve the piezo-and pyroelectricity of polymers. Lam and Chan [2005] studied the influence of lead magnesium niobate-lead titanate (PMN-PT) particles on the ferroelectric properties of a PVDF-TrFE matrix. The piezoelectric and pyroelectric coefficients were measured in the electrical field direction. The Curie point of PVDF-TrFE and PMN-PT is around 105 and 120°C, respectively. Different polarization procedures are possible. As the signs of piezoelectric coefficients of ceramic and copolymer are opposite, the poling conditions modify the piezoelectric properties of the sample. In all cases, the increase in the longitudinal piezoelectric strain coefficient, 33, with ceramic phase poled) at < / = 0.4, the piezoelectric coefficient increases up to 15 pC/N. The decrease in da for parallel polarization is due primarily to the increase in piezoelectric activity of the ceramic phase with the volume fraction of PMN-PT. The maximum piezoelectric coefficient was obtained for antiparallel polarization, and at < / = 0.4 of PMN-PT, it reached 30pC/N. 

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