Studies On Apatite-type Lanthanum Silicate And Doping With Yttrium/Neodymium

The apatite-type lanthanum silicate La10-xSi6O27-1.5x(0≤x≤0.67) were preparedby solid state reaction method and sol-gel method. The La site doping with rare earthelements Y/Nd were investigated. The prepared compounds were characterized withXRD. Its conductivity was measured with AC impedance method and the coefficientof thermal expansion was measured with a thermal dilatometer. The results showed asfollows:The impurities were detected with XRD when x is less than0.15in thecompounds powder of La10-xSi6O27-1.5xsynthetised by solid state reaction method. Thesintering temperature of the silicates systhesized with sol-gel method was lowerthan that with solid phase reaction method. The conductivity of La10-xSi6O27-1.5xincrease with the decrease of x. The conductivity of La9.85Si6O26.775is highest, whichis up to1.7×10-2S· cm-1at800℃.The conductivity decreases when massiveimpurities appeared for x less than0.15. The activation energy of electrical conductioncalculated was in the range from0.83to0.90eV. The thermal expansion coefficient ofLa10-xSi6O27-1.5xwere lowered with the increase of La/Si ratio, where La9.33Si6O26、La9.7Si6O26.55and La10Si6O27have the value of8.672×10-6、8.902×10-6and9.102×10-6/℃respectively at800℃.The maximum amount of Y doped at La site of La9.7-xYxSi6O26.55is less than4.5.The conductivity reduced but the the activation energy of electrical conductionincreased with the increase of doping amount of Y, and its value were estimated0.97,1.07,1.16and1.35eV for La8.7YSi6O26.55, La7.7Y2Si6O26.55, La6.7Y3Si6O26.55andLa5.7Y4Si6O26.55respectively. The thermal expansion coefficient of La8.7YSi6O26.55was8.909×10-6/℃at800℃.The maximum amount of Nd doped at La site of La10-xNdxSi6O27is less than9.5.The conductivity reduced with the increase of Nd doped amount, except for thecompound with x=5. The activation energy of electrical conduction was between0.83eV and0.90eV estimated. The thermal expansion coefficient determined withLa9NdSi6O27and La8Nd2Si6O27were9.226×10-6/℃and9.321×10-6/℃at800℃respectively.