Synthesis and characterisation of In-doped MnWO4-type solid-solutions: Mn1-3xIn2x□xWO4 (x=0-0.11)

Substitution of In3+ for Mn2+ in MnWO4, which is one of the most studied multiferroics, was conducted systematically by solid-state reactions at 1050 degrees C to obtain a series of Mn(1-3x)In2x square xWO4 solid solutions (x=0-0.11; the box indicates vacancy). The successful In-doping could be proven by electron microprobe, and statically disordered structures of this solid solution series were elucidated by Rietveld analyses with X-Ray powder diffraction (XPD) data. Its average structure maintains the space group P2/c at least up to the replacement of 33 at% Mn. The tendency of their unit cells proportionally enlarging with In-doping is an unexpected observation because In3+ is smaller than Mn2+. This could not be explained alone by average atomic bonding distances and angles evaluated from XPD data analyses. Complimentarily, micro-Raman spectra of Mn(1-3x)In2x square xWO4 materials feature a hardening of Raman modes due to stronger atomic bonds in W2O4 and WO2 units with increasing In-doping. This is considered as an inevitable consequence of broken bonding in directly neighbouring Mn-O bonds as the presence of In3+ in MnWO4 accompanies the creation of defects at Mn sites. The current study using XRD and micro-Raman suggests the enlarging local space around the bridging oxygen as the reason for the unexpected cell expansion when smaller In3+ along with defects replace Mn2+ in MnWO4. (C) 2014 Elsevier Inc. All rights reserved.