Phase transitions with extremely small tetragonal distortion in substitution systems of CoV2O4 by high-angular-resolution synchrotron powder diffraction

Abstract Spinel-type CoV 2 O 4 compound shows cubic-to-tetragonal phase transition with a very small distortion (1 – c / a T * ∼ 90 K. The other structural phase transition accompanied by change in space group occurs at T 2  = 59 K. In this study, we investigated the substitution effects on successive structural phase transitions using the high-angular-resolution powder diffraction technique to clarify the origin of these unique phase transitions. In the Cr substitution system Co(V 1– x Cr x ) 2 O 4 (0 ≤  x  ≤ 0.25), while both of these structural transitions were suppressed, they disappeared at different x values. By contrast, in the Mn substitution system (Co 1– x Mn x )V 2 O 4 (0 ≤  x  ≤ 0.2), both of them remained. It was suggested that the phase transitions at T * and T 2 are dominantly related to the magnetic phase transition and orbital degree of freedom of V 3+ ions, respectively.