Phase composition, Raman spectra, infrared spectra and dielectric properties of Li 2 MgTi 1-x (Mg 1/3 Nb 2/3 ) x O 4 ceramics at microwave frequency

The Li2MgTi1-x(Mg1/3Nb2/3)xO4 (0 ≤x ≤ 0.5) ceramics were prepared by the conventional solid-state method. The relationship among phase composition, substitution amount and microwave dielectric properties of the ceramics was symmetrically investigated. All the samples possess the rock salt structure with the space group of Fm-3m. As the x value increases from 0 to 0.5, the dielectric constant linearly decreases from 16.75 to 15.56, which can be explained by the variation of Raman spectra and infrared spectra. The Q·f value shows an upward tendency in the range of 0 ≤x ≤ 0.3, but it then decreases when x > 0.3. In addition, the temperature coefficient of resonant frequency (τf) is shifted toward zero with the increasing (Mg1/3Nb2/3)4+ addition. By comparison, the Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at 1400 °C can achieve an excellent combination of microwave dielectric properties: εr = 16.19, Q·f = 160,000 GHz and τf = −3.14 ppm/°C.