Structural Chemistry and Electronic Properties of the Hexagonal Perovskites BaIr1−xCoxO3−δ (x=0.5, 0.7, 0.8)

✍ Scribed by Jaap F. Vente; Peter D. Battle

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 331 KB
• Volume: 152
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.8664

✦ Synopsis

The room temperature crystal structures of three compositions in the system BaIr 1 ؊ x Co x O 3 ؊ (x ‫؍‬ 0.5, 0.7, 0.8) have been determined from X-ray and neutron powder di4raction data. BaIr 0.5 Co 0.5 O 3.02(1) , BaIr 0.3 Co 0.7 O 2.84(1) , and BaIr 0.2 Co 0.8 O 2.83(1) adopt 12R, 10H, and 5H perovskite structures, respectively; the distribution of Co and Ir cations over corner-sharing and facesharing sites has been determined, and the Co/Ir+O bond lengths have been used to assign the cation oxidation states as Ir 5؉ and Co 3؉ /Co 4؉ . Arguments based on bond lengths and magnetic susceptibility data have been used to assign spin states; at room temperature BaIr 0.5 Co 0.5 O 3؊ contains both high-spin and lowspin Co 3؉ . The distribution of anion vacancies has been determined for x ‫؍‬ 0.7, 0.8; in the latter case there is evidence for the replacement of some BaO 3 layers in the pseudo-hcp structure by BaO 2 layers, thus introducing tetrahedral transition metal sites which are found to be occupied by Co. Neutron di4raction experiments carried out at 5 K revealed a monoclinic distortion in the x ‫؍‬ 0.5 sample, with the environment of the high-spin Co 3؉ cation undergoing a Jahn+Teller distortion. The structures of the x ‫؍‬ 0.7, 0.8 phases did not change signi5cantly on cooling. Measurements of magnetization as a function of applied 5eld suggest that spin glass or cluster glass behavior is present in x ‫؍‬ 0.5, 0.7 below 50 K. In the case of x ‫؍‬ 0.8, magnetization and neutron di4raction data suggest the formation of a weak ferromagnet with a saturation magnetization of 0.60 B per Co cation at 5 K.