Atomic scattering amplitudes for electrons
Atomic scattering amplitudes for electrons
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电子的原子散射振幅
DOI：
10.1107/s0365110x58000475
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发表时间：
1958
期刊：
影响因子：
--
通讯作者：
J. Ibers
中科院分区：
文献类型：
--
作者：
J. Ibers
0.68 A102 = 1.32 J~，低于该间距可预期起皱为4.00 J ~。在对Na N B 0 a及其与K-NbO a、Cd 0.5Nb0 a和Pb 0.5Nb0 a固溶体的结构转变的研究中（Francombe &刘易斯，1957），发现多单电池变成单电池的温度随组成的不同而变化，从800 ℃以上开始。低于室温。在此温度下的晶格间距（可称为起皱转变温度）在每种情况下均接近3.94 μ m。在AgNb 0a和AgTaO 3中，相应的实验值分别为3.96小时和3-95小时，分别铁电或反铁电效应在AgNbO 3的结构转变中只起很小的作用。在钙钛矿结构中可以判断铁电性能的一个标准是居里点结构渡越离子的不连续性质。因此，当将晶胞参数相对于温度作图时，对于强铁电体的BaTi 03、CrK-NbO 3或反铁电体的PbZr 03等物质，在居里温度下明显存在非常明显的不均匀性。KNb 08在居里温度下显示出1-6%的突然线性失真（Shirane等人，1954）与26 μ C. cm. -9（Triebwasser & Halpern，1955）。AgNb_（0a）在325 ° C时，fl从90 °到90 ° 15'的不连续变化。对应于0.2%的线性失真，并且观察到的自发极化也很小。AgTa 0a在370 ℃时发生结构转变。是比较平滑的，这可能表明没有铁电性。在这一点上，值得注意的是，AgTa 0a在与AgNbOa的固溶体中的效果是降低了电阻率的测量值。在AgTa 0a中，在高温下观察到的结构变化可能几乎完全由离子堆积效应引起。
0.68 A, 02= 1.32 J~, the spacing below which puckering can be expected is 4.00 ,~. In an examinat ion of the s tructural t ransit ions of N a N b 0 a and its solid solutions with K-NbOa, Cd0.sNb0a, and Pb05Nb0a (Francombe & Lewis, 1957) it was found tha t the temperature at which the mult iple uni t cell becomes single varies with composition from above 800 ° C. to below room temperature. The lattice spacing at this temperature, which m a y be called the puckering transition temperature, was in each case found to be close to 3.94/~. In AgNb0a and AgTaO3 the corresponding experimental values are 3.96 .h and 3-95 h., respectively. Ferroelectric or antiferroelectric effects appear to p lay only a minor role in the s tructural t ransit ions of AgNbO 3. One criterion by which ferroelectric properties can be judged in the perovskite structures is the discontinuous nature of the Curie-point structure transit ion. Thus when unit-cell parameters are plotted against temperature, for substances like BaTi0a cr K-NbO3 which are strongly ferroelectric, or PbZr03 which is antiferroelectric, a very sharp discont inui ty is apparent at the Curie temperature. KNb08 shows a sudden l inear distortion of 1-6% at the Curie temperature (Shirane et al., 1954) associated with a spontaneous polarization of 26 #C.cm. -9 (Triebwasser & Halpern, 1955). For AgNb0a the discontinuous change of fl from 90 ° to 90 ° 15' at 325 ° C. corresponds to a l inear distortion of 0.2%, and the spontaneous polarization observed is also small. Wi th AgTa0a the structure t ransi t ion at 370 ° C. is comparat ively smooth and this probably indicates the absence of ferroelectricity. In this connection it is notable tha t the effect of AgTa0a in solid solution with AgNbOa is to lower the measured values of permitt ivi ty. In AgTa0a the changes in structure observed at high temperatures probably arise almost ent irely from ionic packing effects.