Disorder- and correlation-induced charge carriers localization in oxyborate MgFeBO4, Mg0.5Co0.5FeBO4, CoFeBO4 single crystals

The temperature dependence of the resistivity of single crystalline Mg1−xCoxFeBO4 samples with x = 0.0, 0.5, 1.0 is investigated for the temperature range (210–400 K). The conduction was found to be governed by Mott variable-range hopping (VRH) in the low-temperature range (T = 210–270 K) and by thermo-activation mechanism in the high-temperature range (T = 280–400 K). Microscopic electronic parameters, such as the density of the localized states near the Fermi level, localization length, the hopping length, and the activation energy have been obtained. The change of the activation energy observed at high-temperature range was attributed to local structure distortions around Fe and Co atoms. The complicated behavior of charge transfer mechanisms is discussed based on two approaches: atomic disorder and electron correlations.This work has been financed by Council for Grants of the President of the Russian Federation (Project Nos. NSh-2886.2014.2, SP-938.2015.5), Russian Foundation for Basic Research (Project Nos. 13-02-00958-a, 13-02-00358-a, 14-02-31051-mol-a). The work of one of coauthors (M.S.P.) was supported by the grant of KSAI “Krasnoyarsk Regional Fund of Supporting Scientific and Technological Activities” and by the Program of Foundation for Promoting the Development of Small Enterprises in Scientific and Technical Sphere (“UMNIK” program). Financial support from the Spanish MINECO MAT11/23791 and DGA IMANA project E-34 is acknowledged.Peer reviewe