Portal de Periódicos da CAPES

Evidence of relaxation of Jahn-Teller polarons above T C in La 1- x Sr x MnO 3 (0.1< xleq 0.5)

1999; IOP Publishing; Volume: 11; Issue: 30 Linguagem: Inglês

10.1088/0953-8984/11/30/313

1361-648X

Dipten Bhattacharya, Amitava Chakraborty, H. S. Maiti,

Rare-earth and actinide compounds

We report the resistivity ()-temperature (T) patterns in La1-xSrxMnO3 (0.1<x0.5) systems over a temperature regime of 20-1273 K. Apart from a general trend of metallic -T pattern below TC (Curie point) and insulating above it, we have observed a re-entrant metallic -T pattern beyond a characteristic temperature T* above TC for the compositions 0.25 x0.50. Such behaviour possibly reflects the relaxation of Jahn-Teller (JT) polarons (which form as a result of splitting of Mn3+ 3d outer levels and associated distortion in MnO6 octahedra) at a higher temperature. The polaron formation energy EJT has been calculated from fitting a simple two-channel conduction model with the resistivity data. It appears to vary significantly with the Sr2+ ion concentration (x) or the concentration of JT-active Mn3+ ions which reflects the variation of the extent of Jahn-Teller coupling. The relaxation of polarons and the change in the behaviour of -T pattern above T* are not associated with any commensurate magnetic transition which seems to be supporting the notion that Jahn-Teller polarons influence the properties like TC, conductivity, magnetoresistivity etc significantly.