Synthesis and physical properties of new oxide AgMnO2
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A novel oxide AgMnO2 was prepared from LiMnO2 via Ag+ → Li+ exchange in the eutectic melt AgNO3-KNO3. It crystallizes in a monoclinically distorted unit cell (SG C2/m) caused by the Jahn-Teller (J-T) ion Mn3+ (3d 4). The structure was refined by isotypy with the crednerite CuMnO2. There are two long axial Mn–O of 264.2(0) pm and four equatorial bonds of 192.7(3) pm and Mn–O–Mn adjoining (83.07°) are bent below the ideal angle. The thermal variation of the magnetic susceptibility (χ/T −1) obeys a Curie-Weiss law with manganese in a trivalent, high spin (HS) state accommodated in elongated MnO6 octahedra (14.8%). Direct coupling between Mn3+ involves negative exchange interactions through long-range antiparallel moments with a temperature θ p = −436 K and a magnetic moment of 5.26 μB/Mn3+ slightly larger than the spin only moment. The title oxide is stable in air up to ∼680 °C before it decomposes into metal silver. It displays a semi-conducting behavior with an activation energy of ∼0.45 eV, characteristic of a conduction by low mobility polarons between Ag+/2+ where nearly all polarons are bonded. The photoelectrochemical properties of AgMnO2 have been investigated by photocurrent technique in 1 M KOH. The cathodic photocurrent J ph provides unambiguous evidence of p-type character attributed to oxygen insertion (0.025 oxygen by formula unit) as required by the charge compensating mechanism. The valence band is made up of Ag−4d wave functions positioned at ∼5.14 eV below vacuum. A comparison with CuMnO2 was also reported.
KeywordsMnO2 High Spin Small Polaron Photoelectrochemical Property Edge Shared Octahedra
This work was supported financially be the Faculty of Chemistry (Algiers) under the contract N° E1602/04/2000. The authors are grateful to Mr A. Mokhtari for his general assistance.
- 7.Handbook of chemistry and physics, 78th edn. 1997–1998. Editor-in-Chief David R. Lide, CRC PressGoogle Scholar
- 9.Fraga S, Karwowski J, Saxena KMS (1976) Handbook of atomic data. Elsevier Scientific Publishing Company, AmsterdamGoogle Scholar
- 11.Shannon RD (1976) Acta Cryst A32:751Google Scholar
- 13.Tabushi M, Ado K, Koyashi H, Kageyama H, Masquelier C, Kondo A, Kano R (1998) J Electrochem Soc 145(4):L46Google Scholar
- 15.Day P, Robine R (1966) Adv Inorg Chem 10:247Google Scholar