Direct evidence of the existence of Mn³⁺ ions in MnTiO₃

¹ School of Basic Sciences, Indian Institute of Technology Mandi - Kamand, Himachal Pradesh-175005, India
² School of Engineering, Indian Institute of Technology Mandi - Kamand, Himachal Pradesh-175005, India

^(a) bindu@iitmandi.ac.in (corresponding author)

Received: 4 June 2017
Accepted: 18 September 2017

Abstract

We investigate the room temperature electronic properties of MnTiO₃ synthesised by different preparation conditions. For this purpose, we prepared MnTiO₃ under two different cooling rates, one is naturally cooled while the other is quenched in liq.nitrogen. The samples were studied using optical absorbance, photoemission spectroscopy and band structure calculations. We observe significant changes in the structural parameters as a result of quenching. Interestingly, in the parent compound, our combined core level, valence band and optical absorbance studies give evidence of the Mn existence in both 2+ and 3+ states. The fraction of Mn³⁺ ions has been found to increase on quenching MnTiO₃ suggests an increase in oxygen non-stoichiometry. The increase in the fraction of the Mn³⁺ ions has been manifested a) as slight enhancement in the intensity of the optical absorbance in the visible region. There occurs persistent photo-resistance when the incident light is terminated after shining; b) in the behaviour of the features (close to Fermi level) in the valence band spectra. Hence, the combined analysis of the core level, valence band and optical absorbance spectra suggests that the charge carriers are hole like which further leads to the increase in the electrical conductivity of the quenched sample. The present results provide a recipe to tune the optical absorption in the visible range for its applications in optical sensors, solar cell, etc.