Effect of oxygen content on properties of the HoBaCo2O5+δ layered cobaltite

In this work we present the result of the first experimental investigation of the role of oxygen content on the properties of the HoBaCo2O5+delta layered cobaltite. We have measured the variation of oxygen content as a function of temperature and oxygen partial pressure by means of thermogravimetry coupled to chemical titration analysis. On selected samples of accurately known oxygen content we have undertaken a systematic investigation of their structural, thermal, and magnetic properties by means of x-ray diffraction, differential scanning calorimetry, and magnetometry. The overall results gained by this study confirm the central role of oxygen content on the properties of these materials suggesting that, for the Ho composition, even very slight variation of the order of delta=0.01 has a dramatic influence on the magnetic and transport properties of the samples. In addition, we have presented results showing the strategy to check the quality of samples prepared at selected oxygen contents by annealing procedures.