Developing high-Q × f value MgNb_(2–x)Ta_(x)O_(6)(0≤x≤0.8) columbite ceramics and clarifying the impact mechanism of dielectric loss: Crystal structure, Raman vibrations, microstructure, lattice defects, chemical bond characteristics, structural parameters, and microwave dielectric properties in-depth studies

摘要

With the increasing frequency of wireless mobile communication,dielectric materials with higher Q×f are required to enhance the signal strength of microwave passive devices and thus compensate for the rapid attenuation of high-frequency signals during propagation.In order to improve the Q×f of the MgNb2O6 system and study the internal mechanism between the structure and microwave dielectric properties,Ta5+ion is introduced to design and fabricate MgNb_(2-x)Ta_(x)O_(6)(0≤x≤0.8)ceramics by the solid-state reaction method.The single columbite phase and dense structure are observed throughout the entire composition range.All elements(Mg,Nb,Ta,and O)can be detected by X-ray photoelectron spectroscopy.Insights from the Raman spectroscopy and group theoretical analysis reveal that the Ag(2)and Ag(3)modes located at∼905 cm−1 dominate the Raman vibration.In addition,theɛr depends on the polarizability reflected by the C–M equation and Raman shift.Theτf closely relates to the bond energy of the Nb/Ta–O bond and restoring force characterized by average octahedral distortion of[Nb/TaO6].Notably,the crucial factors for the huge improvement of Q×f are clarified deeply,in terms of the lower internal strain,the reduced ordering-induced domain size,and the chemical bond valence closer to the ionic valence state,which promotes the stability of crystal structure.Moreover,the introduction of lower electronegative ions enhances the ability of electrons to compensate for oxygen vacancies,thereby reducing the dielectric loss caused by the conductance.Excellent microwave properties(ɛr=19.2,Q×f=170,000 GHz,andτf=−55.6 ppm℃–1)are achieved in MgNb1.4Ta0.6O6 ceramic,specifically a nearly 40%increase in the Q×f.This work has enriched the theory associated with low dielectric loss and provided the MgNb_(1.4)Ta_(0.6)O_(6) ceramic with a pretty high-Q×f for the application in the design of the 5G/6G wireless communication devices.