Microstructural control of microwave dielectric properties in CaTiO3-La(Mg1/2Ti1/2)O3 ceramics -: art. no. 064103
Microstructural control of microwave dielectric properties in CaTiO3-La(Mg1/2Ti1/2)O3 ceramics -: art. no. 064103
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DOI：
10.1063/1.1856212
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发表时间：
2005-03-15
影响因子：
3.2
通讯作者：
Freer, R
中科院分区：
文献类型：
--
作者：
Kipkoech, ER;Azough, F;Freer, R
采用固相反应法制备高密度xCaTiO(3)-(1-x)La(Mg1/2Ti1/2)O-3陶瓷（x=0.0 ~ 1.0）。用扫描电镜、x射线衍射和透射电镜对产物进行了表征。CaTiO3-La(Mg1/2Ti1/2)O-3陶瓷在整个组成范围内形成固溶体，没有二次相的证据。大多数陶瓷的对称性与Pbnm空间群是正交的。La(Mg1/2Ti1/2)O-3端元表现出Mg2+和Ti4+阳离子（在八面体位置）的1:1顺序叠加在钙钛矿畸变上，导致与P2(1)/n空间群的单斜对称。在x=0.3时，Mg2+和Ti4+阳离子的远程1:1阶被破坏。随着CaTiO3含量的增加，材料的变形程度、晶胞体积和晶格应力均降低。在所有的陶瓷中都观察到由冷却时的结构相变产生的孪相畴和反相畴。随着CaTiO3含量的增加，双畴密度增加，但单个畴的尺寸减小。根据孪晶边界处的对称元素将孪晶畴分为{112}和（110）两种孪晶类型。微波介电特性（在3.5 ~ 5.5 GHz）与组分有很强的相关性。相对介电常数（epsilon(r)）和谐振频率温度系数（TCf）随CaTiO3含量的增加呈非线性增加(epsilon(r) 29 ~ 170；TCf -50至+710 ppm/℃)。相比之下，Qf （GHz）值随CaTiO3含量（48000 -5790）近似线性下降。在x=0.55时，epsilon(r)=44.6, Qf=32 000 GHz， TCf接近于零（1.06 ppm/℃）。相对介电常数和TCf随CaTiO3含量的增加而增加，与组分诱导的晶格应力的降低有关，并与宏观极化率的增加有关。(C) 2005美国物理研究所。
High-density xCaTiO(3)-(1-x)La(Mg1/2Ti1/2)O-3 ceramics (x=0.0-1.0) were prepared by solid-state reaction. The products were characterized by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. CaTiO3-La(Mg1/2Ti1/2)O-3 ceramics formed solid solutions throughout the compositional range with no evidence of a secondary phase. For most ceramics the symmetry was orthorhombic with Pbnm space group. The La(Mg1/2Ti1/2)O-3 end member exhibited 1:1 ordering of Mg2+ and Ti4+ cations (in octahedral sites) superimposed on the perovskite distortions leading to monoclinic symmetry with P2(1)/n space group. Long-range 1:1 order of Mg2+ and Ti4+ cations was destroyed at x=0.3. The degree of distortion, unit-cell volume, and crystal lattice stress decreased with increasing CaTiO3 content. Twin and antiphase domains, generated by structural phase transitions on cooling, were observed in all the ceramics. Twin domain density increased with CaTiO3 content but the size of individual domains decreased. The twin domains were classified according to the symmetry elements at the twin boundaries as {112} and (110) twin types. The microwave dielectric properties (at 3.5-5.5 GHz) showed a strong dependence on composition. The relative permittivity (epsilon(r)) and temperature coefficient of resonant frequency (TCf) increased nonlinearly with CaTiO3 content (epsilon(r) 29-170; TCf -50 to +710 ppm/degrees C). In contrast Qf (GHz) values decreased approximately linearly with CaTiO3 content (48 000-5790). Near zero TCf (1.06 ppm/degrees C) was attained at x=0.55, where epsilon(r)=44.6 and Qf=32 000 GHz. The increase in relative permittivity and TCf with CaTiO3 content correlated with the reduction in composition-induced lattice stress in association with increasing macroscopic polarizability. (C) 2005 American Institute of Physics.