Temperature-induced A–B intersite charge transfer in an A-site-ordered LaCu3Fe4O12 perovskite

Abstract

Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties. Chemical doping is the conventional way of modulating these valence states. In ABO(3) perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magnetoresistance. When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer-and, hence, valence changes-by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure. Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu(3)Fe(4)O(12); the underlying intersite charge transfer is accompanied by considerable changes in the material's structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu(2+)(3)Fe(3.75+)(4)O(12) with Fe(3.75+) ions at the B site to LaCu(3+)(3)Fe(3+)(4)O(12) with rare Cu(3+) ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion.

Negative thermal expansion materials: technological key for control of thermal expansion

“…This oxide has NTE of α = −82 ppm K −1 at T = 320-380 K (figure 7). A similar NTE was observed for LaCu 3 Fe 4 O 12 [32][33][34], which results from the charge transfer from Fe to Cu upon heating.…”

“…This was a theoretical attempt to explain magnetovolume effects from the viewpoint of atomic radius contraction. NTE arising from atomic radius contraction has been discovered recently in perovskite oxides [32][33][34][35] [35] undergoes a first-order phase transition from the larger-volume low-T phase to the smaller-volume high-T phase. The volume change reaches 2.9%.…”

Negative thermal expansion of ReO3 in the extended temperature range

“…1,6-10 The NTE materials have generated significant scientific and commercial interest because they can be used to compensate the more usual positive thermal expansion ͑PTE͒ of usual materials. In recent years intense investigations of materials scientists have led to the discovery of several new materials [11][12][13] that show NTE behavior.…”

Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity

“…Many interesting properties have been found in these compounds, leading to potential applications in various fields. For instance, CaCu 3 Ti 4 O 12 and CaMn 3−x Cu x Mn 4 O 12 show an anomalously high dielectric constant and a giant magneto-resistance, respectively [4,5,[7][8][9]; LaCu 3 Fe 4 O 12 is a negative thermal expansion material [10]; and CaCu 3 Ru 4 O 12 exhibits high metallic electrical conductivity [11,12]. Figure 1 shows the crystal structure of CaCu 3 Ru 4 O 12 .…”