New Oxidation States and Defect Chemistry in the Pyrochlore Structure

Abstract

The introduction of anion vacancies into complex metal oxides is a powerful method of controlling structure and properties by tailoring metal coordination environment and oxidation state. The hydride anion can effect reductive transformations of oxides inaccessible to conventional metal getters or gaseous reducing agents.[1] The A 2 B 2 O 7 pyrochlore structure [2] is important for properties as diverse as anion and mixed conduction, [3] superconductivity, [4] and colossal magnetoresistance, [5] but, in contrast to ABO 3 perovskite, there is little chemistry established for the low-temperature introduction of anion vacancies and generation of associated defect structures. Pyrochlore is well known for stabilizing high oxidation states on the octahedral B site; A ). Here we report the systematic low-temperature synthesis of pyrochlore systems with up to 90 % titanium(iii) on the octahedral sites.

Phase Formation and Properties in the System Bi2O3:2CoO1+x:Nb2O5

“…[49][50] Pyrochlore compounds are known to exhibit a wide range of cooperative magnetic properties and, for example, are of significant interest as "spin-ice" systems. [51][52][53] …”

Crucial Role of Site Disorder and Frustration in Unusual Magnetic Properties of Quasi-2D Triangular Lattice Antimonate Na4FeSbO6

“…Tackling such a problem experimentally requires the use of local probe measurements in addition to bulk probe measurements, because the latter are insensitive to a small amount of disorder. A particularly challenging case to deal with is antisite disorder, which often takes place when a system contains cations of similar sizes [20][21][22][23][24][25][26]. The present work is concerned with the antisite disorder in the layered oxide Na 4 FeSbO 6 [27].…”

An Unexpected Crystal‐Chemical Principle for the Pyrochlore Structure

“…[1] A large number of pyrochlore analogs have been synthesized with an amazing variety of chemical compositions and exploitable properties. [3][4][5][6][7][8][9] These include ferroelectricity, [4,10,11] temperature-stable high-permittivity properties, [12,13] fast-ion oxygen conductivity, [6][7][8] and a wide variety of electrical properties including metallic conductivity, semiconductivity, superconductivity, and electronic phase transitions. [4,5,[14][15][16][17][18] The threefold symmetry of the metal arrangement in the crystal structure leads to interesting and diverse magnetic-ordering properties such as ferromagnetism, antiferromagnetism, and spin-glass behavior; [19][20][21] colossal magnetoresistance (CMR) has also been observed.…”