## 4 Conclusions  
The \(M^{2+}N^{4+}\)Nb\({}_{2}\)O\({}_{8}\) (where \(M\) = Mg, Ca, Mn, Co, Ni, Zn and \(N\) = Ti, Zr) ceramics exhibit remarkable microwave dielectric properties. However, their inherently high sintering temperatures pose challenges for their application in low-temperature co-fired ceramic (LTCC) technologies. To address this limitation, a strategic approach involving the partial substitution of Cu\({}^{2+}\) and the addition of LiF was employed to explore the feasibility of achieving low-temperature sintering. Through a meticulously designed series of orthogonal experiments, it was discovered that Cu\({}_{0.3}\)Zr\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) ceramic, characterized by an impressively high quality factor, could be successfully densified at 950 \({}^{\circ}\)C with the assistance of LiF. Specifically, the ceramic doped with 40 mol% LiF, when sintered at 950 \({}^{\circ}\)C for 4 h, exhibited exceptional microwave dielectric characteristics, including a relative permittivity (\(\epsilon_{r}\)) of 32, a quality factor (\(Q\) \(\times\) \(f\)) of 45,543 GHz, and a temperature coefficient of resonant frequency (\(\tau_{f}\)) of \(-\)43.5 ppm/\({}^{\circ}\)C. Furthermore, our studies revealed no adverse chemical reactions between silver and the 40 mol% LiF-doped Cu\({}_{0.3}\)Zr\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) ceramic, confirming their compatibility. In summary, this work presents an effective strategy to reduce the sintering temperature of \(M^{2+}N^{4+}\)Nb\({}_{2}\)O\({}_{8}\) ceramics to an LTCC-compatible level of 950 \({}^{\circ}\)C. The 40 mol% LiF-doped Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) ceramic emerges as a promising candidate for LTCC applications, offering a viable solution to the temperature constraints associated with traditional sintering processes. Additionally, ongoing research is focused on exploring the specific applications of this material. **Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/mai7246251/s1](https://www.mdpi.com/article/10.3390/mai7246251/s1)]([https://www.mdpi.com/article/10.3390/mai7246251/s1](https://www.mdpi.com/article/10.3390/mai7246251/s1)), Figure S1: Mapping Spectra of Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\) Nb\({}_{2}\)O\({}_{8}\) ceramic; Table S1: Refined crystal structure parameters of Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) supplemented with y mol% LiF and residual factors; Figure S2: XPS spectra of Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) supplemented with 50 mol% LiF; Figure S3: EDS analysis of Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) supplemented with 20 mol% LiF; Figure S4: EDS analysis of Cu\({}_{0.3}\)Zn\({}_{0.7}\)Ti\({}_{0.2}\)Zr\({}_{0.8}\)Nb\({}_{2}\)O\({}_{8}\) supplemented with 40 mol% LiF with Ag cofired. **Author Contributions:** Conceptualization, X-H.M. and Q.Q. ; methodology, Q.Q. ; software, Q.Q. and Z.Z. ; validation, Q.Q. and X.-H.M.; formal analysis, Q.Q. and Z.Z. ; investigation, Q.Q. ; resources, X.-H.M. and H.W. ; data curation, X.-H.M. and Q.Q. ; writing--original draft preparation, X.-H.M. and Q.Q. ; writing--review and editing, X.-H.M.; visualization, Q.Q. ; supervision, X.-H.M., H.W., Z.Z. and X.M. ; project administration, X.-H.M.; funding acquisition, X.-H.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by Shandong Provincial Natural Science Foundation of China, grant number ZR2020 QE039. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.