NiMn ₂ O ₄ revisited: Temperature‐dependent cation distribution from in situ neutron diffraction and thermopower studies

The cation distribution of the NTC thermistor spinel N i M n 2 O 4 $NiM{n}_2{O}_4$ was studied in temperature range from 55°C to 900°C, using a combined in-situ neutron diffraction and thermopower study. Rietveld refinements data reveal dependence degree inversion with an parameter 0.70(1) at 900°C 0.87(1) 55°C. Thermopower measurements were evaluated modified Heikes formula [Mn4+]/[Mn3+]-ratio on octahedral sites structure calculated considering spin orbital degeneracy. disproportionation parameter, determined independently as function temperature, used calculate whole range. At high within stability spinel, is characterized by moderate concentration B + $Ni_B^{2 }$ = 0.71(2) small tendency towards 3 $Mn_B^{3 0.98(2). 55°C, enhanced illustrated large 0.87(2), 0.24(2) content indicates extensive Mn-disproportionation. Finally, conclusions regarding possible ageing mechanisms this important material are drawn. This article protected copyright. All rights reserved