Effect of crystal structure of Ca2AMg2Ge2VO12 (A = Y, Eu) garnets on microwave dielectric properties

Abstract

The optimal microwave dielectric properties of Ca 2 AMg 2 Ge 2 VO 12 (A = Y, Eu) garnets are reached at the sintering temperature of 1300 °C for 6 h ( ε r = 10.1, Q × f = 65,600 GHz and τ f = −53 ppm/℃ for Ca 2 YMg 2 Ge 2 VO 12 ; ε r = 9.4, Q × f = 37,900 GHz and τ f = −55 ppm/℃ for Ca 2 EuMg 2 Ge 2 VO 12 ). The dielectric loss of Ca 2 AMg 2 Ge 2 VO 12 (A = Y, Eu) has been measured at a frequency of 13 GHz, and the dielectric loss of these ceramics is mainly affected by the pore volume and atomic packing fraction. The Ca-O and Mg-O bonds are compressed, while the Y-O, Eu,-O, Ge-O, and V-O bonds are in an expanded state. The higher ε r (C-M) calculated by the Clausius-Mossotti (C-M) equation than the measured ε r is attributed to the compression state of 24c-site (Ca 2 /A). The negative τ f value of Ca 2 AMg 2 Ge 2 VO 12 is derived from the positive τ αm value greater than 3 α L . And the slight difference in τ f of Ca 2 YMg 2 Ge 2 VO 12 and Ca 2 EuMg 2 Ge 2 VO 12 is also slightly compressed at the Ca/A-site.