Os 4+ Instability in the Pyrochlore Structure: Tl 2- x Bi x Os 2 O 7- y

• Published in: Inorganic chemistry 2020-01, Vol.59 (2), p.1227-1233
• Main Authors: Converse, Elizabeth Sobalvarro, Li, Jun, Haskel, Daniel, LaBarre, Patrick G, Ramirez, Arthur P, Subramanian, M A
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b02939

Osmium-containing oxides are rare due to the difficulty in stabilizing complex structures with a fixed stoichiometry and metastability of the phases. Bismuth-substituted thallium osmate pyrochlore samples, Tl Bi Os O , were synthesized using solid-state reactions where the solubility limit was found to be approximately = 1.4. Members of this solid solution were characterized by their structural, electronic, magnetic, and thermal properties to understand the influence of Bi substitution on the ground state. The Os-containing pyrochlores crystallize in the ideal cubic pyrochlore structure ( 3 ), and the lattice parameter was found to slightly increase as a function of Bi content. A possible interplay between structure and cation valence states was explored using both neutron powder diffraction and X-ray absorption spectroscopy, suggesting that a combination of Os /Os and Tl /Tl mixed valency throughout the solid solution allows for the stabilization of the pyrochlore structure. The system is metallic for the entire solid solution and predominantly exhibits temperature-independent paramagnetism. Specific heat measurements show an enhanced Sommerfeld coefficient, a possible flat-band signature. This system gave insight into the bonding preferences of Os, indicating a dependence on high oxidation states and mixed valence for the stability of complex structures.