Structure and Properties of Ir-Containing Oxides with Large Spin–Orbit Coupling: Ba₂In_2–xIr_xO_5+δ

Abstract

In this work, the solid solution series Ba2In(2-x)Ir(x)O5+δ (x = 0-1.4, 2) was synthesized, and its structural, magnetic, and charge-transport properties were measured. With increasing Ir content, three transitions in the room-temperature structure were observed: orthorhombic to tetragonal to cubic to a monoclinic distortion of a hexagonal BaTiO3 structure. Neutron diffraction shows Ba2In(1.6)Ir(0.4)O5.4 to be cubic and Ba2InIrO6 to be monoclinic, the latter contrary to previously published X-ray diffraction refinements. Magnetization measurements show Curie-Weiss behavior for x = 0.2-0.6, which arises from nearly 50:50 ratio of Ir(V) and Ir(VI). To our knowledge, this is the first time Ir(VI) has been stabilized with standard solid-state methods under ambient conditions. The electrical resistivity measurements show all the compounds studied are semiconducting and that resistivity decreases with increasing Ir content, suggesting the proximity to a metal-insulator transition. A sign reversal in the high-temperature Seebeck coefficient is observed indicating both electron and hole charge transport.

Photocatalytic CO2 reduction by Cr-substituted Ba2(In2-Cr )O5·(H2O) (0.04 ≤ x ≤ 0.60)

“…Ba 2 In 2 O 5 has drawn increasing research interest regarding fast oxide ion and proton conduction due to its unique crystal structure [1][2][3][4][5][6]. Partial cationic and/or anionic substitution in Ba 2 In 2 O 5 brings marked changes in crystal structure, defect structure, and electronic structure resulting in a number of materials properties, which are interesting for various technical applications [2,[7][8][9][10][11][12][13][14][15][16][17][18][19]. For example, gallium or zirconium substituted Ba 2 In 2 O 5 for solid oxide fuel cells (SOFC) with an intermediate operating temperature range of 823 -1023 K was a research focus in recent years [13,[20][21][22].…”

“…For example, gallium or zirconium substituted Ba 2 In 2 O 5 for solid oxide fuel cells (SOFC) with an intermediate operating temperature range of 823 -1023 K was a research focus in recent years [13,[20][21][22]. Lately, the magnetic properties of Ir-, Mn-, and Cosubstituted Ba 2 In 2 O 5 were investigated [7,23,24]. Mn 5+ with paramagnetic spin-only moments [23].…”

The effect of iridium oxidation state on the electronic properties of perovskite-type solid solutions: Ba2–La InIrO6 and BaLaIn1–Ca IrO6

“…One might suggest that the charge separation is too small. However, no ordering is observed in the Ba 2 In 2-x Ir x O 5+δ family [26] where the charge difference is 2 or greater. Additionally, ordering is known to occur based solely on difference in ionic radii of the B cations in several A 2 B 4+ B' 4+ O 6 (A 2+ = Ba, Sr; B 4+ = Ce, Tb, Pr; B' 4+ = Ir, Pt) double perovskites [42][43][44].…”

“…The most common state is Ir(IV) though it is not difficult to stabilize Ir(V) and even Ir(VI) under the right conditions [26][27][28][29][30][31]. Ir(III) is most common in transition metal complexes but a few examples of extended oxide structures include BaIrO 3-δ , K 1-x Ir 4 O 8 and Sr 2-x La x IrO 4 [32][33][34].…”

“…It is also a possibility that BaInIrO 6 and BaLaCaIrO 6 possess a small amount of Ir(VI) due to the presence of electropositive ions (i.e. Ba 2+ and Ca 2+ ) which are known to stabilize higher Ir oxidation states[20,26,57].…”