Ramarao S D, Murthy V R K
Microwave Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai - 600 036, India.
Dalton Trans. 2015 Feb 7;44(5):2311-24. doi: 10.1039/c4dt02364a.
Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4 (x = 0.0-1.0) compositions were synthesized via conventional solid-state reaction method. Structural and lattice vibrational characteristics of these compositions were studied with the help of powder X-ray diffraction and Raman spectroscopic measurements. Rietveld refinements confirm the formation of all these compositions in monoclinic wolframite structure with P2/c space group. When moving towards Ni(2+)-poor compositions, splitting in the X-ray reflections was observed and is explained with lattice parameter variation. With increasing value of x, Raman spectra show two additional Raman active modes and the possible reasons for observing these modes are discussed in terms of electronegativity difference of the randomly distributed cations in B-site of these compositions. X-ray photoelectron spectroscopic measurements were done to understand the chemical bonding states of different elements in these compositions. Surface morphology studies reveal that the average grain size increases with increasing x. Microwave dielectric properties such as dielectric constant and quality factor were measured using Hakki-Coleman and reflection cavity techniques and enhancement in these values with x is correlated with intrinsic parameters such as polarizability and 3d electrons present in the constituent ions of these compositions. Temperature coefficient of resonant frequency was measured using an invar cavity attached to a programmable hot plate and is explained with B-site octahedral distortion of these compositions. Well dense Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4 (x = 0.0-1.0) compositions possess good microwave dielectric properties.
通过传统的固态反应法合成了Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4（x = 0.0 - 1.0）组合物。借助粉末X射线衍射和拉曼光谱测量研究了这些组合物的结构和晶格振动特性。Rietveld精修证实所有这些组合物均形成具有P2/c空间群的单斜钨铁矿结构。当向贫Ni(2+)组合物转变时，观察到X射线反射出现分裂，并通过晶格参数变化进行解释。随着x值的增加，拉曼光谱显示出另外两种拉曼活性模式，并根据这些组合物B位中随机分布阳离子的电负性差异讨论了观察到这些模式的可能原因。进行了X射线光电子能谱测量以了解这些组合物中不同元素的化学键合状态。表面形貌研究表明，平均晶粒尺寸随x的增加而增大。使用Hakki-Coleman和反射腔技术测量了微波介电性能，如介电常数和品质因数，并且这些值随x的增加与诸如极化率和这些组合物组成离子中存在的3d电子等本征参数相关。使用连接到可编程热板的因瓦合金腔测量了谐振频率温度系数，并根据这些组合物的B位八面体畸变进行了解释。致密的Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4（x = 0.0 - 1.0）组合物具有良好的微波介电性能。
