Phase evolution and electronic properties of cryptomelane nanorods

Potassium functionalized cryptomelane-type manganese oxide (K-OMS-2) is gaining more and more attention due to its exceptional catalytic, electronic, magnetic and ion transport properties. It is therefore of great importance to have a general picture of the changes this material undergoes with the increase of the temperature in reducing and oxidizing atmospheres. Potassium cryptomelane was synthesized by the reflux method in the reaction of manganese(II) acetate and potassium permanganate. It was characterized by means powder X-ray diffraction and Raman spectroscopy at characteristic stages of high-temperature treatment, determined by means of thermogravimetric analysis. Moreover, the mobility of potassium and thus induced changes of electronic properties were determined by using temperature programmed potassium desorption experiments and by following work function changes at elevated temperatures. The presented results can be used as a guideline for potential application limits, where the operation temperature and atmosphere play a crucial role. (C) 2018 Elsevier B.V. All rights reserved.