## 1 Introduction  
With the accelerated advancement of 5G and forthcoming 6G technologies, millimeter-wave devices have emerged as a focal area of research on a global scale, attributed to their exceptional ultra-high-speed transmission rates and low latency in communication processes. Microwave dielectric ceramics, distinguished by their superior performance characteristics within the millimeter-wave frequency range, exhibit substantial practical utility across a multitude of communication systems, including radar systems, base station infrastructures, GPS navigational aids, and satellite communications [1; 2; 3; 4; 5; 6]. In accordance with the specific requirements of practical applications, microwave dielectric materials must possess the following critical attributes: they must exhibit appropriate dielectric constants (\(\epsilon_{r}\)) to facilitate the minimization of device dimensions or the mitigation of signal propagation delays, possess high quality factors (\(Q\times f\)) to effectively curtail signal attenuation, and demonstrate a near-zero temperature coefficient of resonant frequency (\(\tau_{f}\)) to enhance the reliability and stability of device applications [7; 8; 9; 10]. Low-temperature co-fired ceramic (LTCC) technology, as a form of multi-layer ceramic manufacturing, has emerged as the preeminent approach in the realm of passive integration. This technology is favored for its ability to embed passive components within the ceramic substrate, thereby delivering exceptional radio frequency (RF) performance while enabling device miniaturization [11; 12]. The utilization of silver, characterized by its low melting point of approximately 960 \({}^{\circ}\)C, as the metal electrode in compact multi-layer ceramic structures represents a prevalent and efficacious choice, given its cost-effectivenessand superior electrical conductivity. Consequently, to ensure the thermal stability and integrity of silver electrodes during the sintering process, the sintering temperature of LTCC materials is typically controlled to be below 960 \({}^{\circ}\)C, with a common practice being to limit it to \(\leq\)950 \({}^{\circ}\)C. This approach ensures that the silver electrodes do not undergo premature melting or degradation, thereby preserving the overall performance and reliability of the LTCC-based devices. In recent years, the utilization of microwave dielectric ceramics with medium dielectric constants has become increasingly prevalent in satellite communications, mobile base stations, and various other applications. Among these, the \(M^{2+}N^{4+}Nb_{2}O_{8}\) system (where \(M\) = Mg, Ca, Mn, Co, Ni, Zn, and \(N\) = Ti, \(Z\)r) has emerged as a highly promising ceramic material, attributed to its exceptional dielectric characteristics. For instance, [PERSON] et al. reported ZnZrNb\({}_{2}O_{8}\) ceramics sintered at 1325 \({}^{\circ}\)C for 6 h, exhibiting microwave dielectric properties with \(\varepsilon_{r}\) = 26.55, \(Q\)\(\times\)\(f\) = 68,300 GHz, and \(\tau_{f}\) = \(-\)32.92 ppm/\({}^{\circ}\)C [13]. Subsequently, [PERSON] et al. substituted Zr\({}^{4+}\) ions with smaller Ti\({}^{4+}\) ions, resulting in ZnZr\({}_{0.8}\)Ti\({}_{0.2}\)Nb\({}_{2}\)O\({}_{8}\) ceramics sintered at 1150 \({}^{\circ}\)C with even more outstanding properties: \(\varepsilon_{r}\) = 29.75, \(Q\)\(\times\)\(f\) = 107,303 GHz, and \(\tau_{f}\) = \(-\)24.41 ppm/\({}^{\circ}\)C [14]. However, the sintering temperatures of these reported \(M^{2+}N^{4+}Nb_{2}O_{8}\) ceramics remain excessively high for application in the realm of low-temperature co-fired ceramic (LTCC) technology. Therefore, there is an urgent need to reduce their sintering temperatures to below 960 \({}^{\circ}\)C, thereby fulfilling the primary requirement for LTCC compatibility. In our previous studies, we emphasized the beneficial effects of strategically removing trace amounts of high-melting-point precursor materials as an effective means to lower the sintering temperature of microwave dielectric ceramics [12].