## 3 Results and Discussion
The permittivity increased with increasing temperature, reaching a maximum of 19.3 at 1200 \({}^{\circ}\)C and after that decreasing. Thus, increasing sintering temperature does not always result in a higher permittivity (\(\varepsilon_{r}\)). The permittivity of the well-sintered (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) ceramics ranged from 17.9 to 19.3 at 1125-1200 \({}^{\circ}\)C. A maximum \(\varepsilon_{r}\) value of 19.3 was reached for the (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) sintered at 1200 \({}^{\circ}\)C for 4 h.  
The Q\(f\) value is a crucial index for microwave dielectric ceramics applications because a high Q\(f\) value represented a lower dielectric loss for microwave devices. Q\(f\) values increased when temperature increased from 1125 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C (Figure 6), consistent with the variation of bulk density, as shown in Figure 5. The increase of Q\(f\) value at low temperatures is attributed to the rise in density identical to grain growth uniformity, as shown in Figure 3. A maximum Q\(f\) value of 165,000 (GHz) was observed for the (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) ceramics sintered at 1200 \({}^{\circ}\)C for 4 h. Q\(f\) value reached a maximum at 1200 \({}^{\circ}\)C, and after that, it decreased. The Q\(f\) value degraded due to the inhomogeneous grain growth, which leads to a reduction of density, as mentioned in Figure 3. There are several possible mechanisms to cause microwave dielectric loss, such as the lattice vibrational modes, the pores, second phases, impurities, and lattice defects [35]. Furthermore, apparent density also closely affects the dielectric loss and has also been demonstrated in microwave dielectric mate  
Figure 5: Dependent relationship of apparent density(g/cm\({}^{3}\)) and relative density (%) of the (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{1-y}\)Ni\({}_{y}\)TiO\({}_{3}\) ceramics with y = 0.01–0.2 under 1125–1250 \({}^{\circ}\)C.  
rials [35; 36]. The \(Q\)/\(\gamma\) value and the variation of density of the (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) show a similar trend, and hence apparent density is one of the dominant factors to cause the dielectric loss in this ceramic system. As illustrated in Figure 7, the temperature coefficient of resonance frequency (\(\tau_{f}\)) of (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{1-y}\)Ni\({}_{y}\)TiO\({}_{3}\) at temperatures ranging from 1125 to 1250 \({}^{\circ}\)C with x = 0.01-0.2 \(\tau_{f}\) values fluctuate slightly at the whole temperature range. As expected, the synthesized composition persisted unchanged, and hence no noticeable fluctuation of the \(\tau_{f}\) value was shown. As we know, \(\tau_{f}\) is positively related to the synthesized composition, the second phase, and the material's additive. The measured \(\tau_{f}\) values were from \(-62.9\) to \(-66\) ppm/\({}^{\circ}\)C as the (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) sintered at 1125-1250 \({}^{\circ}\)C. At 1200 \({}^{\circ}\)C, a \(\tau_{f}\) of (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{0.95}\)Ni\({}_{0.05}\)TiO\({}_{3}\) with 4 h sintering time was measured around \(-65.4\) ppm/\({}^{\circ}\)C. From the above discussion, microwave dielectric performance of (Mg\({}_{0.6}\)Zn\({}_{0.4}\))\({}_{1-y}\)Ni\({}_{y}\)TiO\({}_{3}\) with various y value sintered at 1200 \({}^{\circ}\)C for 4 h was shown in Table 2 further demonstrated that best performance was found for y = 0.05. We also observed that \(Q\)/\(\gamma\) value is sensitive to Ni content, and however, permittivity and \(\tau_{f}\) remain slightly fluctuate with varied Ni content. The sintering temperature affects the permittivity and \(Q\)/\(\gamma\) value to some extent. However, \(\tau_{f}\) is not sensitive to sintering temperature. Table 3 revealed the comparison of the proposed dielectric with other similar documented dielectric ceramics.