Guo Dan, Zhou Di, Li Wen-Bo, Pang Li-Xia, Dai Yan-Zhu, Qi Ze-Ming
Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi'an Jiaotong University , Xi'an 710049, Shaanxi, China.
Department of Materials Science and Engineering, University of Sheffield , Sheffield S1 3JD, U.K.
Inorg Chem. 2017 Aug 7;56(15):9321-9329. doi: 10.1021/acs.inorgchem.7b01462. Epub 2017 Jul 26.
In the present work, a series of low-temperature firing scheelite structured microwave dielectric in water-insoluble LaO-NbO-VO system was prepared via the traditional solid-state reaction method. Backscattering electron diffraction, X-ray diffraction (XRD), energy-dispersive analysis, and Rietveld refinements were performed to study the phase evolution and crystal structure. In the full composition range of (1 - x)LaNbO-xLaVO (0 ≤ x ≤ 0.9) ceramics, at least four typical phase regions including monoclinic fergusonite, tetragonal sheelite, B-site ordered sheelite, and composite of monoclinic LaVO and tetragonal sheelite phases can be detected according to XRD analysis. The variations of relative dielectric constant ε, quality factor Q × f, and resonant frequency τ could be attributed to Nb/V-O bond ionicity, lattice energy, and the coefficient of thermal expansion. Infrared reflectivity spectra analysis revealed that ion polarization contributed mainly to the permittivity in microwave frequencies ranges. Furthermore, the 0.7LaNbO-0.3LaVO ceramic sintered at 1160 °C possessed excellent microwave dielectric properties with an ε of ∼17.78, a Q × f of ∼75 940 GHz, and a τ of ca. -36.8 ppm/°C. This series of materials might be good candidate for microwave devices.
在本工作中，通过传统的固态反应法制备了一系列水不溶性LaO-NbO-VO体系中具有白钨矿结构的低温烧结微波介质材料。利用背散射电子衍射、X射线衍射（XRD）、能谱分析和Rietveld精修来研究相演变和晶体结构。根据XRD分析，在(1 - x)LaNbO-xLaVO（0 ≤ x ≤ 0.9）陶瓷的整个组成范围内，至少可以检测到四个典型的相区，包括单斜烧绿石、四方白钨矿、B位有序白钨矿以及单斜LaVO和四方白钨矿相的复合物。相对介电常数ε、品质因数Q × f和共振频率τ的变化可归因于Nb/V-O键离子性、晶格能和热膨胀系数。红外反射光谱分析表明，在微波频率范围内，离子极化对介电常数的贡献主要。此外，在1160 °C烧结的0.7LaNbO-0.3LaVO陶瓷具有优异的微波介电性能，ε约为17.78，Q × f约为75940 GHz，τ约为 -36.8 ppm/°C。这一系列材料可能是微波器件的良好候选材料。
