Synthesis and physical properties of new oxide AgMnO2

A novel oxide AgMnO2 was prepared from LiMnO2 via Ag+ fi 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+ (3d4). 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 (v/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 longrange antiparallel moments with a temperature hp = –436 K and a magnetic moment of 5.26 lB/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 Jph 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