Bond theory, vibrational spectroscopy, and dielectric responses of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics

This study established the connection between structure and dielectric responses by synergistically evaluating the chemical bond characteristics and lattice vibrational spectroscopies of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics. The MgTa2O6 ceramic exhibits a uniform grain size distribution and a dense microstructure, with dielectric characteristics at microwave range of a εr value of 27.27, a high Q×f value of 109,203  GHz (8.73 GHz), and a τf of approximately 53.38 ppm/oC when sintered at 1300 oC, while the NiTa2O6 ceramic presents a smaller average grain size and minor micropores, with dielectric characteristics at microwave range of εr = 24.58, Q×f = 27,610 GHz (9.25 GHz), and τf = 33.94 ppm/oC, sintered at 1250 oC. The structural refinement and atomic arrangements confirm a trirutile structure along the [001], [100], and [3 3¯1¯] zone axes. Ta–O bonds are found to contribute the most to the ionic character of a bond, bond susceptibility, lattice stability, thermal expansion behaviors, and strength of bonding ability, indicating their significant influence on dielectric polarization, lattice stability, and temperature coefficient of resonant frequency. Raman scattering spectra analysis reveals that the A1g mode near 700 cm−1 mainly controls the Raman vibrational behaviors. The theoretical dielectric properties calculated from the infrared spectrum and dielectric properties analysis consistent with the measured dielectric performances, suggesting that the dielectric characteristics at the microwave range are mainly determined by the oscillatory absorption of structural phonons, with the first two modes at 210.48 cm−1 and 232.87 cm−1 contributing 72.02% to the εr value and 90.45% to the tanδ value, respectively.