On the absence of bipolarons in manganese perovskites

The paramagnetic phase of La0.65Ca0.35MnO3 and La0.65Pb0.35MnO3 powders was investigated by electron spin resonance. The resonance spectra, for a range of temperatures, was used to examine the presence of polarons and bipolarons. The resonance lines are compatible with the presence of polarons (g≈2), but the characteristic high-spin bipolaron lines (g≈4) are absent. The results are inconsistent with the presence of high-spin bipolarons. The evidence with respect to low-spin bipolarons is less conclusive, although the temperature dependence of the resonance line parameters speaks against the presence of low-spin bipolarons.