Phase formation, microstructure and microwave dielectric properties of Li2SnO3-MO (M=Mg, Zn,) ceramics

Phase formation, microstructure and microwave dielectric properties of (1-x) Li2SnO3-xMO (M=Mg, Zn) ceramics have been investigated using x-ray powder diffractometer (XRD), scanning electron microscope (SEM) and a network analyzer at the frequency of about 8-12GHz in this paper. The results showed that Li2SnO3 formed limited range of solid solution ((beta-Li2SnO3(ss)) with MgO doping (x <= 0.1) or ZnO doping (x <= 0.3). Multiphase of Li4MgSn2O7, beta-Li2SnO3 (ss) and alpha-Li2SnO3(ss) existed in the compositions of x=0.2-0.5 for MgO-added specimens. ZnO second phase appeared when x>0.3 for the ZnO-added specimens. Dense and homogeneous microstructure could be obtained for the ZnO-doped composition with x=0.3. The dielectric permittivity decreased with the increase of MgO doping content, but increased with the increase of ZnO dopant within the miscible compositional range (beta-Li2SnO3(ss)). The presence of Li4MgSn2O7 or ZnO second phase reduced the dielectric permittivity. The doping of ZnO improved the Q x f value of beta-Li2SnO3(ss), whereas the doping of MgO slightly decreased the Q x f value. The improvement of Q x f value could be ascribed to the stabilization of the ordering-induced domain boundaries by the partial segregation of the larger doping cation. The tau(f) value changed from positive into negative value with increasing MgO or ZnO addition and near zero tau(f) value (4.67 or -0.27 ppm/degrees C) could be obtained at x=0.3 composition for MgO or ZnO added specimens, respectively.