Effect of binary ion substitution on the crystal structure and microwave dielectric properties of MgTa2O6 ceramics

Mg 1/3 A1 1/3 A2 1/3 Ta 2 O 6 ceramics (where A1 and A2 represent Co, Ni, or Zn) were prepared using the solid-phase reaction route. The results of X-ray diffraction and Raman tests showed that (Co 1/2 Ni 1/2 ) 2+ , (Co 1/ 2 Zn 1/2 ) 2+ , and (Ni 1/2 Zn 1/2 ) 2+ ions replaced Mg 2+ ions in the lattice of MgTa 2 O 6 , resulting in the formation of a pure tri-rutile structure. All three complex ions could significantly reduce the sintering temperature of the ceramics (by 150°C–200°C) and could broaden the sintering window. The large deviation (48.8%–69.2%) between the porosity corrected relative permittivity ε r-corr. and the theoretical relative permittivity ε r-theo. might be due to the overestimation of the ionic polarizability of Ta 5+ by Shannon. (Co 1/2 Ni 1/2 ) 2+ has the most significant effect of increasing the bond energy of ceramic A–O bonds, reducing the τ f value from 51 to 36 ppm/°C. In addition, the mechanisms affecting their dielectric properties are discussed based on bond ionicity ( f i ), full width at half maximum (FWHM) of Raman peak, and bond energy ( E ). Mg 1/3 Co 1/3 Ni 1/3 Ta 2 O 6 ceramic sintered at 1350°C have the most excellent microwave dielectric properties: ε r = 26.8, Q × f = 86,000 GHz, and τ f = 36 ppm/°C.