The role of ionic sizes in inducing the cubic to tetragonal distortion in AV$_{2}$O$_{4}$ and ACr$_{2}$O$_{4}$ (A=Zn, Mg and Cd) compounds

摘要: Cubic to tetragonal distortion in spinel compounds have been a contentious issue for last two decades. Different groups proposed different mechanisms understand such these spinels, which are: (i) spin lattice coupling mechanism known as the driven Jahn-Teller (JT) effect, (ii) strong relativistic spin-orbit coupling, moderate JT and weak V-V interactions (iii) effect. Now, order know possible cause distortion, we avoided complexities (various among spin, electronic, orbital degrees of freedom) by carrying out unpolarized calculations. The calculated values bulk moduli ZnV$_{2}$O$_{4}$ (ZnCr$_{2}$O$_{4}$), MgV$_{2}$O$_{4}$ (MgCr$_{2}$O$_{4}$) CdV$_{2}$O$_{4}$ (CdCr$_{2}$O$_{4}$) are found be $\sim$289 ($\sim$254), $\sim$244 ($\sim$243) $\sim$230 ($\sim$233) GPa, respectively. For vanadates chromates, parameter $a$ CdV$_{2}$O$_{4}$$>$MgV$_{2}$O$_{4}$$>$ZnV$_{2}$O$_{4}$ CdCr$_{2}$O$_{4}$$>$MgCr$_{2}$O$_{4}$$>$ZnCr$_{2}$O$_{4}$, respectively consistent with experimental results. cubic (c/a), c/a$<$1 $\sim$0.996 ($\sim$0.997), $\sim$0.995 ($\sim$0.994) $\sim$0.997 ($\sim$0.998), These good agreement data ZnV$_{2}$O$_{4}$, MgV$_{2}$O$_{4}$, ZnCr$_{2}$O$_{4}$ MgCr$_{2}$O$_{4}$ compounds. present study clearly shows role ionic sizes inducing spinels. also appear responsible deciding other physical properties