Studies Of Microstructure Of Ta₂O₅and Y₂O₃Dopant On The0.9Al₂O₃-0.1TiO₂-Baesd Microwave Dielectric Ceramics

Firstly, the effects of sintering processes, Ta2O5dopant and sintering temperature on the bulk density and micro-defects of0.9Al2O3-0.1TiO2-based microwave dielectric ceramics has been studied by measuring the density, positron lifetime and coincidence Doppler broadening spectra. The phase compositions, microstructures have been studied by X-ray diffraction and scanning electron microscopy. And then, the effects of processes, Y2O3dopant and sintering temperature on the bulk density and micro-defects of0.9Al2O3-0.1TiO2-based microwave dielectric ceramics has been investigated by measuring the density, positron lifetime and coincidence Doppler broadening spectra. The experimental results are listed as follows:(1) The XRD patterns of the microwave dielectric ceramics xTa2O5-(1-x)(0.9Al2O3-0.1TiO2)(x=0.3wt%,0.6wt%,0.9wt%,1.2wt%,1.5wt%) annealed at at1100℃for12h show that there are two main phases of A12O3and TiO2in the samples, while the Al2TiO5phase disappear. (2) In comparison with the densities of the microwave dielectric ceramics xTa2O5-(1-x)(0.9Al2O3-0.1TiO2)(x=0.3wt%,0.6wt%,0.9wt%,1.2wt%,1.5wt%) sintering at1350℃,1400℃and1450℃, respectively, it has been found that the sample sintering at1450℃can reach a relatively high density. For each sintering temperature, as the x increasing, the density of the sample first decrease and then increase, the density of the sample reaches a minimum value at x=0.9wt%.(3) In the case of xTa2O5-(1-x)(0.9Al2O3-0.1TiO2)(x=0.3wt%,0.6wt%,0.9wt%,1.2wt%,1.5wt%)cereamic, for sample sintering at1350℃, with the x increasing, the second component lifetime τ2of the sample first increases then decreases, and τ2reaches a maximum value at x=1.2wt%, that is, the open volume defect in the sample first increases then decreases, and reach maximum at x=1.2wt%. For sample sintering at1400℃, the second component lifetime τ2of the sample increases with x, that is, the open volume of defect in the sample increases with x. For sample sintering at1450℃, with the x increasing, the second component lifetime τ2first decreases then increases, τ2reaches a minimum value at x=1.2wt%, that is the open volume of micro-defect first decrease then increase and reach minimum at x=1.2wt%.(4) In comparison with the changes of the mean positron lifetime τm, the second component lifetime τ2and its corresponding intensity I2of the xTa2O-(1-x)(0.9Al2O3-0.1TiO2) samples sintered at1350℃,1400℃ and1450℃, respectively, it can be found that the open volume of defects in the sample of x=1.2wt%sintering at1450℃are the smallest, and it can be expected that it possesses a good dielectric property.(5) In comparison with the densities of the microwave dielectric ceramics xY2O3-(1-x)(0.9A12O3-0.1TiO2)(x=0.0wt%,0.4wt%,0.8wt%,1.2wt%,1.6wt%,2.0wt%) sintering at1350℃,1450℃and1550℃, respectively, it can be found that the sample sintering at1550℃can reach a relatively high density. For each sintering temperature, the density of the sample increases with x.(6) In the case of xY2O3-(1-x)(0.9Al2O3-0.1TiO2)(x=0.0wt%,0.4wt%,0.8wt%,1.2wt%,1.6wt%,2.0wt%) cereamic, for sample sintering at1350℃, with the x increasing, the second component lifetime τ2of the sample first increases then decreases, and τ2reaches a maximum value at x=1.2wt%, that is, the open volume defect in the sample first increases then decreases, and reach maximum at x=1.2wt%. For sample sintering at1450℃, the second component lifetime τ2of the sample increases with x, that is, the open volume of defect in the sample increases with x. For sample sintering at1550℃, with the x increasing, the second component lifetime τ2first decreases then increases, τ2reaches a minimum value at x=1.2wt%, that is the open volume of micro-defect first decrease then increase and reach minimum at x=1.2wt%.(7) The experiment results of coincident Doppler broadening spectra of positron annihilation radiation show that In the case of xY2O3-(1-x)(0.9Al2O3-0.1TiO2)(x=0.0wt%,0.4wt%,0.8wt%,1.2wt%,1.6wt%,2.0wt%) cereamic, for sample sintering at1350℃, with the x increasing, the peak of the ratio curve of the sample first decreases then increases, it reaches the minimum at x=0.8wt%, that is, the open volume defect in the sample first increases then decreases, and reach the maximum at x=0.8wt%. For sample sintering at1450℃, the peak of the ratio curve of the sample decreases with x, that is, the open volume of defect in the sample increases with x.