Synthesis Of Gallates And Their Microwave Dielectric Properties

In recent years, with the rapid development of modern communication devices, such asmobile communication, satellite communication, the global satellite positioning system,bluetooth, and wireless local area network (WLA), microwave technology is developingtowards a higher frequency. Microwave dielectric ceramics with low dielectric constants andhigh-Q×f values have been widely used in microwave devices, such as resonators, filters, andoscillators. We had prepared MgGa2O4, ZnGa2O4, Mg(GaxAl1-x)2O4ceramics successfully,then investigated the atomic structure, microstructure of the ceramics as well as therelationship between sintering temperature, composition, microstructures, and microwavedielectric properties based on XRD, SEM, TEM, Raman, FT-IR, XPS.(1) ZnGa2O4ceramics were prepared by solid-state method, and pure ZnGa2O4ceramics wereobtained at950℃. The ZnGa2O4ceramic sintered at1385℃possessed excellent microwavedielectric properties:r=10.4, Q×f=94,600GHz (at13.345GHz), τf=-27ppm/℃.Compared with ZnAl2O4(1550℃:r=8.5, Q×f=56,300GHz, τf=-79ppm/℃), ZnGa2O4has lower sintering temperature, wide sintering range, largerand high Q×f, small negative τfvalue. When sintering temperature was higher than1360℃, two kinds of morphologies existon the surface of ceramic. The growth of grains followed the VLS mechanism.(2) MgGa2O4ceramics were synthesized by solid-state method, and expected pure MgGa2O4phase formed at1185℃. When the sintering temperature was higher than1335℃, graindeveloped fully, uniform microstructure and clear boundary occurred, while the degree ofcation ordering increased with increasing sintering temperature. The above characteristicswere advantageous to improving the microwave dielectric properties of MgGa2O4ceramics.The ceramic sintered at1410℃exhibited excellent microwave dielectric properties:r=9.54,Q×f=117,000GHz (at14.7GHz), τf=-4.0ppm/℃. Compared with MgAl2O4(1550℃:r=8.75, Q×f=68,900GHz, τf=-75ppm/℃), MgGa2O4has low sintering temperature, widesintering range, largerand Q×f value, and small negative τfvalue.(3) Mg(GaxAl1-x)2O4(x=0-1.0) ceramics were synthesized via solid-state method. Effect ofdifferent Ga doping amount and sintering temperature on the relative density of ceramics,microstructure and dielectric properties of Mg(GaxAl1-x)2O4were investigated. Microwave dielectric properties of Mg(GaxAl1-x)2O4(x=0.6) solid solution sintered at1485℃werelisted as follows: r=8.87, Q×f=107,000GHz (at14.8GHz), τf=-16ppm/℃.With Gadoping amount increasing, XRD diffraction peak, Raman and FT-IR spectrum ofMg(GaxAl1-x)2O4ceramics shifted regularly, suggesting formation of perfect Mg(GaxAl1-x)2O4solid-solution.