STUDY OF THE VALENCE TRANSITION IN EU-SUBSTITUTED, YB-SUBSTITUTED, AND CA-SUBSTITUTED SMS UNDER HIGH-PRESSURE AND SOME COMMENTS ON OTHER SUBSTITUTIONS
STUDY OF THE VALENCE TRANSITION IN EU-SUBSTITUTED, YB-SUBSTITUTED, AND CA-SUBSTITUTED SMS UNDER HIGH-PRESSURE AND SOME COMMENTS ON OTHER SUBSTITUTIONS
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DOI：
10.1103/physrevb.19.4154
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发表时间：
1979-01-01
影响因子：
3.7
通讯作者：
MAINES, RG
中科院分区：
文献类型：
--
作者：
JAYARAMAN, A;MAINES, RG
研究了Sm （Sm 1−x M x 2+ S）中Eu、Yb和Ca对Sm的取代作用，以及压力对这些化合物的影响。混合化合物具有半导体性质，在环境压力下，晶格参数没有异常，表明价态转变，需要高压才能影响价态变化。这表明，仅仅有利的取代基尺寸不足以促进价电子的变化，而且取代基的电子结构必须是正确的。高压下的电阻率和体积研究表明，当x< 0.3时，sm1−x Eu x S和sm1−x Ca x S的压力诱导转变为一级，当x< 0.60时，sm1−x Yb x S的压力诱导转变为连续的。在铕和镱取代的SmS中存在两个4 f能级；一个对应于靠近5 d导带的sm4f6和eu4f7，或者位于能隙深处的yb4f14能级。在价跃迁中，只有sm4f6能级是离域的。从目前和早期关于取代的SmS的结果中，提出了三个概括，似乎可以解释稀土和th取代的SmS以及sms1 - x asx化合物的行为。为了解释一阶和连续的过渡，调用了导带中S特征的存在或不存在。
The effect of Eu, Yb, and Ca substitution for Sm in SmS (Sm 1− x M x 2+ S), as well as the effect of pressure on these compounds have been investigated. The mixed compounds, which are semiconducting, show no anomaly in the lattice parameter indicative of a valence transition at ambient pressure, and high pressure is required to affect the valence change. This shows that a favorable size of the substituent alone is insufficient for promoting the valence change, and that the electronic structure of the substituent has to be right. Resistivity and volume studies under high pressure show that the pressure-induced transition is first order in Sm 1− x Eu x S and Sm 1− x Ca x S for x< 0.3, in Sm 1− x Yb x S for x< 0.60 and continuous at higher concentrations. In Eu-and Yb-substituted SmS there are two 4 f levels; one corresponding to the Sm 4 f 6 which lies closer to the 5 d conduction band and the Eu 4 f 7, or the Yb 4 f 14 levels which are located deep in the energy gap. In the valence transition, only the Sm 4 f 6 level is delocalized. From the present as well as earlier results on substituted SmS, three generalizations are proposed, which seem to explain the behavior of rare-earth-and Th-substituted SmS, as well as Sm S 1− x As x compounds. To account for the first-order and continuous transitions, the presence or absence of S character in the conduction band is invoked.