Metal-Insulator Transitions in Anion-Excess LaMnO3+δ Controlled by the Mn4+ Content

✍ Scribed by M. Verelst; N. Rangavittal; C.N.R. Rao; A. Rousset

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 215 KB
• Volume: 104
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1142

✦ Synopsis

(\mathrm{LaMnO}{3+\delta}) samples with (\mathrm{Mn}^{4+}) content up to (50 %) have been prepared by different methods. The structure of (\mathrm{LaMnO}{3+\delta}) changes from orthorhombic to cubic (via rhombohedral) with increase in the (\mathrm{Mn}^{4+}) content. (\mathrm{LaMnO}{3+6}) samples containing greater than (20 % \mathrm{Mn}^{4+}) are ferromagnetic and show resistivity maxima at a temperature (T{\mathrm{t}}) which is close to the ferromagnetic Curie temperature. The resistivity maximum is due to the occurrence of a metal-insulator transition. In samples heated to the same temperature, the value of (T_{t}) increases with (% \mathrm{Mn}^{4+}). For a given sample, (T_{t}) increases with the temperature of heat treatment due to the increase in particle size. The onset of ferromagnetism in (\mathrm{LaMnO}{1+\delta}) accompanied by an insulator-metal transition is similar to that found in (\mathrm{La}{1-\delta} \mathrm{Ca}{5} \mathrm{MnO}{3}) and (\mathrm{La}{1-x} \mathrm{Sr}{x} \mathrm{CoO}_{3}). O 1993 Academic Press. Inc.