Synthesis and physical properties of new oxide AgMnO2

• Published in: Journal of materials science 2007-07, Vol.42 (13), p.4778-4784
• Main Authors: KORICHE, Nesrine, BOUGUELIA, Aissa, MOHAMMEDI, Mohamed, TRARI, Mohamed
• Format: Article
• Language: English
• Subjects: Chemistry; Conduction; Curie-Weiss law; Elements and non-metal compounds (oxides, hydroxides, hydrides, sulfides, carbides, ...); Exact sciences and technology; Exchanging; Inorganic chemistry and origins of life; Jahn-Teller effect; Magnetic moments; Magnetic permeability; Manganese ions; Materials science; Photoelectric effect; Photoelectric emission; Physical properties; Polarons; Preparations and properties; Silver; Unit cell; Valence band; Wave functions
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-006-0741-0

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+ (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 (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 θp = −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 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.