Crystal structure and microwave dielectric properties of alkaline-earth hafnates, AHfO3 (A = Ba, Sr, Ca)
Crystal structure and microwave dielectric properties of alkaline-earth hafnates, AHfO3 (A = Ba, Sr, Ca)
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DOI：
10.1111/j.1551-2916.2007.02134.x
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发表时间：
2008-03-01
影响因子：
3.9
通讯作者：
Lanagan, Michael T.
中科院分区：
文献类型：
--
作者：
Feteira, Antonio;Sinclair, Derek C.;Lanagan, Michael T.
研究了固相法制备的AHfO（3）（A = Ba，Sr，Ca）陶瓷的晶体结构和微波介电性能。X射线衍射和电子衍射表明BaHfO（3）是一种非倾斜的立方钙钛矿（a（0）a（0）a（0），空间群Pm（3）over barm），而SrHfO（3）和CaHfO（3）都是正交畸变的钙钛矿（a（-）B（+）a（-），空间群Pnma）。用X射线衍射法制备了相对密度接近理论密度90%的AHfO（3）陶瓷，其显微结构由随机取向的等轴晶组成。在1750 ℃环6小时。传统的透射电子显微镜显示在CaHfO（3）和SrHfO（3）的亚晶粒显微结构中存在长的平行铁弹畴。在室温和微波频率下，AHfO（3）陶瓷，其中A = Ba，Sr和Ca，具有类似于24.2的ε（r），类似于14250 GHz的Qxf（r（在8.9 GHz）和tau（f）类似于+111 ppm/K; τ（r）类似于23.5，Q x f（r）类似于33534 GHz图10示出了与15950GHz（在8.9GHz）类似的Qx f（r）和与-33ppm/K类似的τ（f）。在立方钙钛矿环境中，Hf（4+）的离子极化率计算为3.32埃（3），而在非立方环境中，它增加到4.36 - 4.47埃（3）。最后，AHfO（3）（A = Ba，Sr和Ca）的介电性能与它们的钛酸盐和锆酸盐对应物进行了比较。
The crystal structure and microwave (MW) dielectric properties of AHfO(3) (A = Ba, Sr, and Ca) ceramics prepared by the solid-state route have been investigated. X-ray and electron diffraction show BaHfO(3) to be an untilted cubic perovskite (a(0) a(0) a(0), space group Pm (3) over barm), whereas SrHfO(3) and CaHfO(3) are both orthorhombically distorted perovskites (a(-) b(+) a(-), space group Pnma). AHfO(3) ceramics with a relative density similar to 90% of the theoretical X-ray density and microstructures consisting of randomly oriented equiaxed grains were prepared by. ring at 1750 degrees C for 6 h. Conventional transmission electron microscopy reveals the occurrence of long parallel ferroelastic domains in the subgrain microstructure of CaHfO(3) and SrHfO(3). At room temperature and MW frequencies, AHfO(3) ceramics, where A = Ba, Sr, and Ca, have epsilon(r) similar to 24.2, Q x f(r) similar to 14250 GHz (at 8.9 GHz) and tau(f)similar to+111 ppm/K; epsilon(r)similar to 23.5, Q x f(r)similar to 33534 GHz (at 9.3 GHz), and tau(f)similar to-63 ppm/K; and epsilon(r)similar to 21.4, Q x f(r)similar to 15950 GHz (at 8.9 GHz), and tau(f)similar to-33 ppm/K, respectively. The ion polarizability for Hf(4+) in a cubic perovskite environment is calculated to be 3.32 angstrom(3), whereas in a noncubic environment it increases to 4.36-4.47 angstrom(3). Finally, the dielectric properties of AHfO(3) (A = Ba, Sr, and Ca) are compared with their titanate and zirconate counterparts.