Crystal structure and microwave dielectric properties of Mg1.8R0.2Al4Si5O18 (R=Mg, Ni, Zn, Cu, Sr, Ca, Ba) ceramics

In this study, the element substitution technique was utilized to create a solid solution, which in turn allowed for the manipulation of lattice parameters. The microwave dielectric properties of Mg1.8R0.2Al4Si5O18 (R=Mg, Ni, Zn, Cu, Sr, Ca, Ba) ceramics were investigated following the substitution of Mg2+ ions. The influence of microstructural alterations on these properties was also examined. A cordierite solid solution was formed when R = Ni, Cu, Sr, or Ba; however, an additional phase emerged when R = Zn, Sr, or Ca. The complete substitution influenced the relative dielectric constant of Mg1.8R0.2Al4Si5O18 due to the ionic polarizability and the average ionic property of the R ion. The Q × f value was found to be related to the crystal lattice energy, while the τf value was primarily affected by octahedral distortion. The appearance of a secondary phase altered the primary factors influencing the dielectric properties of the Mg1.8R0.2Al4Si5O18 ceramics. Among the substitutions tested, Mg1.8Ni0.2Al4Si5O18 exhibited superior microwave dielectric properties with εr = 4.64, Q × f = 44,770 GHz, and τf = −32 ppm/°C.