Dielectric And Conductance Properties Of ZrV_2-xP_xO₇ Series Negative The Rmal Expansion Materials

Most of the materials expand with the increase of temperature,only a few of them show the opposite behavior,which is called negative thermal expansion materials.Material will undergo temperature change in application;thermal stress will be induced by mismatch of expansion coefficient after heating devices made of different materials,which will reduce the physical properties of devices.Combining negative thermal expansion materials with positive thermal expansion materials,zero expansion or controllable thermal expansion materials can be prepared to solve the mismatch of expansion coefficient,which has broad prospects.Anisotropic negative expansion materials are prone to micro-cracks when heated,which will lead to the decrease of strength of materials.Therefore,isotropic negative expansion materials have greater research value.ZrV₂O₇ is one of the most important isotropic negative thermal expansion materials in AM₂O₇ series,which has attracted wide attention in recent years.ZrV₂O₇will undergo phase transformation in the temperature range of 350-375 K.When the temperature is lower than 350 K,ZrV₂O₇ is a 3×3×3 superstructure.When the temperature is higher than 375 K,it will become a 1×1×1 general structure,which exhibits negative thermal expansion property.In order to reduce the phase transition temperature of ZrV₂O₇,Sleight et al substituted P⁵⁺for V⁵⁺to reduce the phase transition temperature of ZrV_2-xP_xO₇?0?x?2?from 375 K?x=0?to 326 K?x=0.3?.However,besides affecting the phase transition and thermal expansion of ZrV₂O₇,P substitution should also affect its other properties,such as dielectric and conductive properties.In this paper,ZrV_2-xP_xO₇ series negative thermal expansion materials were prepared by solid-state sintering,the effect of P substitution on the dielectric and conductive properties of ZrV₂O₇ was studied.Solid state reaction method has been synthesized negative thermal expansion material,ZrV2O7.The dielectric relaxation and temperature-dependent alternating current impedance characteristic were studied.The electrical conductivity shows a linear relationship with temperature from 393 to 573 K,and the activation energy is0.319 eV.The dielectric constant of ZrV₂O₇ is 61.6 at low frequency?<10 KHz?and low conductivity at room temperature;The dielectric constant of ZrV₂O₇ is 15.8 at high frequency?>10 MHz?,which is higher than that of SiO₂ and means that the material can be made high frequency electronic devices or dielectric waveguide coupler.It is found that the high frequency dielectric constant of ZrV_2-xP_xO₇ series decreases with the increase of P content.The ionic relaxation polarization and the grain boundary polarization rate of the materials first increase and then decrease with the increase of P content.The dielectric relaxation time first increases and then decreases with the increase of P content,presenting the largest dielectric relaxation time,5.63×10^-4 s for ZrV_1.6P_0.4O₇.The effect of P substitution on dielectric property of ZrV₂O₇ could relate to the difference of radius and electronegativity of P and V ions,which results the lattice distortion and scattering probability change.The room temperature conductivity of ZrV_2-xP_xO₇ series is very sensitive to the content of P,presenting the highest conductivity,5.83×10^-5 Scm^-1 for ZrV_1.6P_0.4O₇.The activation energy of ZrV_1.6P_0.4O₇ is calculated to be 0.19 eV by variable temperature characteristic test.