Preparation And Microwave Dielectric Properties Of Pr₂(Zr_1-xTi_x)₃（MoO₄）₉ Solid Solution Ceramics

With the rapid rise of wireless information technology represented by 5G,wireless Internet,wireless sensor network and satellite communication positioning system,high-performance microwave devices are now facing ever greater demand.Molybdate microwave dielectric ceramics have been concerned by researchers because of their lower sintering temperature,lower dielectric constant and excellent quality factor.Therefore,to develop new molybdate microwave dielectric ceramic systems and optimize the dielectric properties have become an urgent problem to be solved.In this work,a novel binary molybdate,Pr₂Zr₃（MoO₄）₉,was taken as the research object to explore the crystal structure and microwave dielectric properties,and the performance parameters were adjusted by means of ion-substitution.The main research contents are as follows:Firstly,novel Mo-riched Pr₂Zr₃(MoO₄9) ceramics were prepared by solid-state reaction method,and the microwave dielectric properties were studied for the first time.X-ray diffraction combined with Rietveld refinement results indicated that single-phase Pr₂Zr₃（MoO₄）₉ ceramics,which crystallized in a trigonal system（R（?））,were obtained in the whole sintering temperature range（600–800℃）.SEM images suggested that well-densed Pr₂Zr₃（MoO₄）₉ ceramics could formed at low sintering temperature 650–800°C.The excellent microwave dielectric properties were obtained at Pr₂Zr₃（MoO₄）₉ ceramic sintered at 650℃:ε_r=10.72,Q·f=64,200GHz,τ_f=-13.0 ppm/°C.The chemical bond parameters in Pr₂Zr₃（MoO₄）₉crystal were calculated based on the chemical bond theory of complex crystals.It was found thatε_rwas primarily influenced by the Mo–O bond because of high bond ionicity for Mo–O bond.The stability of the crystal structure was also mainly determined by the Mo–O bond,which possessed high lattice energy and bond energy.On the basis classical harmonic oscillator model,the infrared reflectivity spectra were fitted and the real and imaginary parts of the complex dielectric constant were calculated.Results supported that ion polarization was the main dielectric contributor for Pr₂Zr₃（MoO₄）₉ ceramic at microwave region.For the purpose of improving the dielectric properties,trace Ti⁴⁺ions were introduced into Pr₂Zr₃（MoO₄）₉ ceramics and a series of Pr₂(Zr_1-xTi_x)₃（MoO₄）₉（X=0.02,0.04,0.06,0.08,0.10）microwave dielectric ceramics were prepared.The results suggested that the crystal structure was not changed by doping of Ti⁴⁺within this X range,and the crystal lattice parameters varied little in different components.With the increase of X values,theε_rof Pr₂(Zr_1-xTi_x)₃（MoO₄）₉（X=0.02,0.04,0.06,0.08,0.10）ceramics stabilized at about 11,andτ_ffluctuated between-16ppm/°C and-12 ppm/°C.The Q·f values improved from 53,400 GHz to 80,700GHz,which were largely affected by the average grain size and packing fraction.Typically,optimized properties for Pr₂(Zr_1-xTi_x)₃（MoO₄）₉ ceramics ofε_r=10.73,Q·f=80,700 GHz andτ_f=-14.1 ppm/°C were achieved in X=0.10 when sintered at 800°.In order to further study the effects of Ti⁴⁺substitution on the crystal structure and microwave dielectric properties for Pr₂Zr₃（MoO₄）₉ ceramics,a series of Pr₂（Zr₁-_xTi_x）₃（MoO₄）₉（X=0.1–1.0）solid solutions were prepared.XRD analysis showed that there was no phase transition in the whole composition range,and all samples crystallized in trigonal structure with space group R（?）.When X increased from 0.1 to 1.0,theε_r of Pr₂（Zr₁-_xTi_x）₃（MoO₄）₉ ceramics increased from 10.7 to 16.4,the quality factor Q·f decreased from 80,700 GHz to 18,700 GHz,andτ_fapproached zero（τ_f=-14.1～-2.6 ppm/°C）.The lattice parameters and cell volume of Pr₂（Zr₁-_xTi_x）₃（MoO₄）₉ solid solutions decreased monotonically with the increase of Ti⁴⁺content confirmed by Rietveld refinements.The parameters calculation results indicated that theε_rimproved because increase ofα/V_m;the increase ofτ?values was due to the increase of lattice energy and bond energy of Mo–O bond,and the decrease of B-position bond valence.The decrease in Q·f was related to the increase of intrinsic loss which could be characterized by FWHM of Raman peak.