Perovskite-like Mn2O3: A Path to New Manganites
Perovskite-like Mn2O3: A Path to New Manganites
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DOI：
10.1002/anie.201208553
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Dubrovinsky, Leonid
中科院分区：
文献类型：
--
作者：
Ovsyannikov, Sergey V.;Abakumov, Artem M.;Dubrovinsky, Leonid
在复杂氧化物中，钙钛矿基锰氧化物在科学和技术中发挥着特殊的作用。[1，2]它们表现出巨大的磁阻，[3]并且可以用作存储器和电阻开关元件[4]或多铁性。[5]钙钛矿结构ABO3具有两个不同的阳离子位点：由氧八面体配位的B-位点和立方八面体配位（通常严重扭曲）的A-位点。[6]钙钛矿锰氧化物的磁性和输运性质在很大程度上取决于共角MnO 6八面体的钙钛矿框架中的Mn ± O ± Mn相互作用。虽然A阳离子不直接参与这些相互作用，但它们控制Mn的价态和MnO2-Mn键的几何形状。复杂的现象，如电荷和轨道排序，往往伴随着A-位点上的化学取代。对于采用A或B位置的阳离子，对形式电荷和离子半径的要求通常不同，并防止A/B混合。小的且通常高度带电的过渡金属B-阳离子不利于大的12配位A-位点。然而，在A位有序的钙钛矿AA '3B4 O12（其中A =碱金属、碱土金属、稀土金属、Pb或Bi阳离子，A'= Cu 2+或Mn 3+，和B =过渡金属、Ga、Ge、Sb或Sn）的独特类别中，用过渡金属部分填充A位是可能的。[2，7]这种化合物的关键成分是A '阳离子，它应该倾向于一级Jahn-Teller效应（Cu2+或Mn3+）。在A '位上适合于这种过渡金属阳离子的氧环境是由具有显著大的倾斜幅度的a + a + a+八面体倾斜系统（在Glazer符号中）[8]产生的（例如，在CaCu3Ti4O12中，TiO2-O3-Ti键角仅为140.78）。[9]倾斜产生正方形平面阴离子配位，有利于Jahn-Teller活性A '阳离子。A’和B过渡金属阳离子之间的ap/ap = 3p % 2.15（其中ap是钙钛矿子壳的参数）分离允许通过在常规ABO3钙钛矿中不存在的另外的A’-O-B路径的强电子相互作用。例如，在LaCu3Fe4O12中，这种相互作用导致Cu和Fe阳离子之间的电荷转移的同构相变。[10]其他令人兴奋的性能也被报道为AA '3B4O 12系统，例如，一个大的负的热膨胀在SrCu3Fe4O 12。[11]在AA '3B4O12钙钛矿中，1/4的A-位置仍然被电子惰性阳离子占据。用过渡金属阳离子取代它们将开辟一条通往一类新化合物的途径，其中磁性和输运性质受BNO_3 B和ANO_3 B相互作用的控制。为了合成这类新的钙钛矿，我们研究了Mn2O3在高压高温下的相图（HP-HT）。选择Mn2O3有两个原因：首先，具有由Mn离子填充的阳离子位点7/8的钙钛矿（AMn3Mn4O12）是已知的。[2]其次，Mn阳离子显示出高度灵活的电荷状态和配位环境，因此最终可以容纳在钙钛矿结构的A-位置。例如，Mn 2+阳离子对于A-位置足够大，如具有a + bxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbxbx [12通过HP-HT处理将Mn2O3稳定为钙钛矿结构中的Mn [MnO3]的想法沿着先前在这种条件下制备钙钛矿型二元氧化物的尝试。早期的工作报道了一些二元氧化物（例如Fe 2 O3）中高压驱动的钙钛矿结构稳定化。[14]然而，仔细的单晶原位研究...
Among complex oxides, perovskite-based manganites play a special role in science and technology.[1, 2] They demonstrate colossal magnetoresistance,[3] and can be employed as memory and resistive switching elements [4] or multiferroics.[5] The perovskite structure ABO3 has two different cation sites: B-sites that are octahedrally coordinated by oxygen, and cuboctahedrally-coordinated (often heavily distorted) A-sites.[6] The magnetic and transport properties of perovskite manganites are largely determined by the MnÀOÀMn interactions in the perovskite framework of corner-sharing MnO6 octahedra. Although the A cations do not directly participate in these interactions, they control the Mn valence and the geometry of the MnÀOÀMn bonds. Complex phenomena, such as charge and orbital ordering, often accompany chemical substitutions on the A-site. Requirements on formal charge and ionic radius are usually different for cations adopting the A or B positions and prevent A/B mixing. Small and often highly charged transition-metal B-cations are unfavorable for the large 12-coordinated A-site. Partial filling of the A-position with transition metals is, nevertheless, possible in a unique class of A-site ordered perovskites AA’3B4O12(where A= alkali, alkali-earth, rare-earth, Pb, or Bi cations, A’= Cu2+ or Mn3+, and B= transition metals, Ga, Ge, Sb, or Sn).[2, 7] A key ingredient of such compounds is the A’cation that should be prone to a first-order Jahn–Teller effect (Cu2+ or Mn3+). An oxygen environment suitable for such transition-metal cations at the A’position is created by the a+a+a+ octahedral tilt system (in Glazer s notation)[8] with a notably large magnitude of the tilt (for example, in CaCu3Ti4O12 the TiÀOÀ Ti bond angle is only 140.78).[9] The tilt creates a square-planar anion coordination, favorable for Jahn–Teller-active A’cations. The ap/ffiffiffi 3 p% 2.15 (where ap is a parameter of the perovskite subshell) separation between the A’and B transition-metal cations allows for a strong electronic interaction through an additional A’ÀOÀB path that does not exist in conventional ABO3 perovskites. For example, in LaCu3Fe4O12, this interaction leads to an isostructural phase transition with charge transfer between the Cu and Fe cations.[10] Other exciting properties were also reported for AA’3B4O12 systems, for example, a large negative thermal expansion in SrCu3Fe4O12.[11] In AA’3B4O12 perovskites, 1/4 of the A-positions are still occupied by electronically inactive cations. Their replacement with transition-metal cations would open a route to a novel class of compounds, in which magnetic and transport properties are controlled by both BÀOÀB and AÀOÀB interactions. To synthesize this new class of perovskites, we explored the phase diagram of Mn2O3 at high pressures and high temperatures (HP-HT). Mn2O3 was selected for two reasons: first, perovskites with cation sites 7/8 filled by Mn ions (AMn3Mn4O12) are already known.[2] Second, Mn cations show highly flexible charge states and coordination environments, and thus, could eventually be accommodated in the A-position of the perovskite structure. For example, the Mn2+ cation is sufficiently large for the A-position, as demonstrated by the high-pressure MnVO3 perovskite with the a+bÀbÀ octahedral tilting distortion.[12, 13] The idea of stabilizing Mn2O3 as Mn [MnO3] in the perovskite structure by HP-HT treatment goes along with previous attempts to prepare perovskite-type binary oxides under such conditions. Earlier works reported on highpressure-driven stabilization of perovskite structure in some binary oxides, for example, in Fe2O3.[14] However, careful single-crystal in situ studies …