Madelung Energy and Charge Ordering in β-Phase Vanadate Bronzes
Madelung Energy and Charge Ordering in β-Phase Vanadate Bronzes
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β 相钒酸盐青铜中的马德隆能量和电荷排序
DOI：
10.1143/jpsj.70.309
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发表时间：
2001
影响因子：
1.7
通讯作者：
Y. Ohta
中科院分区：
文献类型：
--
作者：
S. Nishimoto;Y. Ohta
β相钒青铜β-A0.33V2O5(A=Na、Li、Ag、Ca、Sr等)最近引起了人们的极大关注，因为他们推测了与电荷有序(CO)有关的金属-绝缘体(MI)相变。2-5)转变温度TCO从A=Ag的90K到A=Li1-3的180K)由于结构中涉及三个晶体上不等价的V位，并且在相变时观察到V离子的价态发生了剧烈的变化，5)人们首先要问的问题是：T>；TCO的电子在哪里，电子在TCO下面的局域化在哪些位置？能带结构计算将提供有关这一问题的有用信息，但目前还无法获得。因此，在这篇简短的笔记中，我们采用了离子模型，计算了不同电子组态下系统的马德隆能，以便对稳定的电子组态有一定的了解。下面，我们将显示V1位置(VO6八面体的锯齿状链位)是电子被定位的能量最低的位置，V2位置(VO6八面体的梯形位置)次之，V3位置(VO5金字塔的锯齿状链位)是能量最高的。结果的含义将被讨论。β相化合物的晶体结构具有特征的V2O5骨架，沿晶体学b轴由三种无限长链组成(见参考文献图1。2和3)。V1位形成了边共享VO6八面体的锯齿链，V2位形成了角共享VO6八面体的两条梯子。V1链和V2阶梯共享VO6八面体的边。V3位点形成了锯齿状的VO5金字塔链，连接了V1链和V2阶梯。当A=一价阳离子(即，每六个V-离子有一个d电子)时，V离子β-A1/3V2O5的平均价态是V(5−1/6)+，当A=二价阳离子(即，每三个V-离子有一个d电子)时，V(5−1/3)+。在β-Na_(0.33)V_2O_5单晶中证实了T&T_c处沿b轴的准一维(1D)金属电导和TCO处的MI+CO相变。2、5)在低温下(T 50K)，A=Na和Ag中存在反铁磁性长程有序，而在A=Ca和Sr中，反铁磁(AF)长程有序
β-phase vanadate bronzes β-A0.33V2O5 (A=Na, Li, Ag, Ca, Sr, etc.) have recently attracted much attention because of their conjectured metal-insulator (MI) phase transition associated with charge ordering (CO).2-5) The transition temperature TCO ranges from 90K for A=Ag to 180K for A=Li.1-3) Because three crystallographically inequivalent V sites are involved in the structure and drastic change in the valence state of V ions has been observed at the phase transition, 5) the question one has to ask first is: where are the electrons at T > TCO and at which sites do the electrons localize below TCO? The band structure calculations will provide useful information on this issue but they are unavailable at present. In this Short Note, we therefore adopt the ionic model and calculate the Madelung energy of the system for various electron configurations to gain some insight into the stable electron configurations. Below, we will show that the V1 position (zigzag chain sites of VO6 octahedra) is the lowest in energy for the electrons to be located, the V2 position (ladder sites of VO6 octahedra) is the next lowest, and the V3 position (zigzag chain sites of VO5 pyramids) is the highest in energy. Implication of the results will be discussed. The crystal structure of the β-phase compounds has a characteristic V2O5 framework consisting of three kinds of infinite chain along the crystallographic b-axis (see Fig. 1 of refs. 2 and 3). The V1 sites form a zigzag chain of edge-shared VO6 octahedra, and the V2 sites form a two-leg ladder of corner-shared VO6 octahedra. The V1 chain and V2 ladder share the edges of the VO6 octahedra. The V3 sites form a zigzag chain of edgeshared VO5 pyramids, which bridges the V1 chain and V2 ladder. The average valence of V ions β-A1/3V2O5 is V(5−1/6)+ when A=monovalent cations (i.e., there is one d-electron per six V-ions), and V(5−1/3)+ when A=divalent cations (i.e., is one d-electron per three V-ions). Quasi-one-dimensional (1D) metallic conduction along the b-axis at T > Tc and the MI plus CO phase transition at TCO have been confirmed in the single crystal of β-Na0.33V2O5. 2, 5) At low temperatures (T 50K), the antiferromagnetic (AF) long-range order occurs in A=Na and Ag, while in A=Ca and Sr, the