Valence averaging and phase transitions in europium (Eu2VO4) and iron (RSr2Fe3O9) compounds |
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Authors: | I Nowik RH Herber I Felner VPS Awana |
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Institution: | (1) Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel;(2) Instituto de Fisica, Unicamp, 13083-970 Campinas, SP, Brazil |
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Abstract: | Mössbauer studies of 151Eu in Eu2VO4 reveal a very sharp valence averaging phase transition at 450 K. Two equally intense absorption lines, differing in isomer shift by 12.7 mm/s, corresponding to Eu2+ and Eu3+, collapse to a single absorption line at the average isomer shift. The transition is confirmed by X-ray and resistivity measurements. In RSr2Fe3O9 (R=Pr, Sm) 57Fe studies reveal averaging valence phase transitions coinciding with magnetic order phase transitions at 190 K and 140 K, respectively. Two magnetic sextets, corresponding to 2Fe3+ + Fe5+, collapse to two singlets corresponding to 2Fe4+ + Fe3+. |
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