Electrical and dielectric behavior of Pb(Mg 1/4 Ni 1/4 W 1/2 )O 3 ceramics
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Electrical and dielectric behavior of Pb(Mg1/4Ni1/4W1/2)O3 ceramics Adolfo Franco Júnior Núcleo de Pesquisa em Química, Universidade Católica de Goiás, Caixa Postal 86, 74605-010 Goiânia-GO, Brazil Email: [email protected]
ABSTRACT In this study full dense polycrystalline samples of Pb(Mg1/4Ni1/4W1/2)O3 have been sintered by solid-state reaction. X-ray data showed the formation of a single-phase new compound with unit cell parameters a = 9.8045 (25) Å, b = 13.1280(25) Å and c = 14.4207 (25) Å. Scanning electron microscopy (SEM) was used to evaluate the microstructures of sintered specimens. Dielectric constant and loss as function of frequency were investigated.
INTRODUCTION The Pb-based perovskite compounds such as PbTiO3, Pb(ZrTi)O3, Pb(MgNb)O3 etc. are important for wide ranging applications [1-13]. Extensive literature survey on Pb-based complex perovskite shows that, except a few studies, not much work has been reported on complex PbWO3 and PbMoO3 because of their high electrical conductivity and dielectric loss at low frequency and at high temperature. Lately a diffuse phase transition has also been observed in many complex tungstate/molybdate [14-16] ceramics modified with alkali and rare-earth ions. Sinha et al. [17] has studied the existence of the ferroelectric-paraelectric phase transitions in the compounds of a general formula Pb(B’1/4B’’1/4B’’’1/2)O3 where B’= alkaline earth ions, B’’ = transition ions and B’’’ = tungsten or molybdenum ions. They found a dielectric anomaly and ferroelectric phase transition observed at 76°C on the compound Pb(Mg1/4Ni1/4W1/2)O3. Also they observed that the dielectric constant and loss dramatically decreased with frequency (200104Hz) at room temperature. The high value of dielectric constant and loss at lower frequencies it may be attributed to the fact that their specimens were not fully dense material. The presence of large amount of pores and defects in the bulk and or/or at the surface of the material can develops a considerable amount of space charge polarization contributing to an increase of ε value and loss particularly at low frequencies and high temperatures. Therefore in the present communication, we report preliminary sintering studies on Pb(Mg1/4Ni1/4W1/2)O3 compounds (hereafter PMNW) in order to obtain full dense ceramics to understand better their microstructure and to investigate their relaxor behavior and diffuse phase transition.
EXPERIMENTAL PROCEDURE Polycrystalline samples of PMNW were prepared by solid-state reaction technique using high purity component oxides: PbO (powder,
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