Microwave dielectric properties of high-entropy [(Mg1/2Zn1/2)0.4+x(Ni1/3Co1/3Mn1/3)0.6-x]2TiO4 ceramics

In this study, a series of high-entropy [(Mg 1/2 Zn 1/2 ) 0.4+ x (Ni 1/3 Co 1/3 Mn 1/3 ) 0.6- x ] 2 TiO 4 (expressed as MZNCMT) (0.0 <= x <= 0.6) ceramics were prepared via the solid-state reaction, the high-entropy ceramics exhibited inverse spinel structure. The phase compositions, microstructures, and microwave dielectric properties were investigated. The results of x-ray diffraction (XRD) showed that a principal phase of [(Mg 1/2 Zn 1/2 ) 0.4+ x (Ni 1/3 Co 1/3 Mn 1/ 3)0.6-x]2TiO4 ceramics, whereas the second phase of (Mg, Zn, Ni, Co, Mn)TiO3 appeared when x <= 0.4. With the increase of x value, the relative density of the sample decreased, the unit cell volume first decreased and then kept expanding. This phenomenon could be attributed to the reduction of (Ni 1/3 Co 1/3 Mn 1/3 ) 2 + . Good microwave dielectric properties were achieved: x = 0.0 (epsilon r = 17.17, Qf = 16500 GHz, zf = -33 ppm/degrees C), x = 0.5 (epsilon r = 16.30, Qf = 53900 GHz, zf = -30 ppm/degrees C) and x = 0.6 (epsilon r = 16.26, Qf =110800 GHz, zf = -39 ppm/degrees C). The epsilon r value of MZNCMT ceramics is consistent with the theoretical dielectric constant (epsilon theo), indicating that epsilon r is mainly based on ion polarization. The Qf value were highly related to the packing fraction. Furthermore, the zf value depended on the bond strength of A-site.