Combined influences of A3+ and Mo6+ on monoclinic-orthorhombic phase transition of negative-thermal-expansion A2Mo3O12

Abstract More reports about monoclinic-orthorhombic (m-o) phase transition of A 2 M 3 O 12 are focusing on the influences of radius as well as electronegative of A 3+ . However, m-o phase transition temperatures (PTTs) of A 2 Mo 3 O 12 do not always increase or decrease with radius/electronegative of A 3+ (A-Sc, Al, Cr, In, Fe). Considering the combined influences of electronegativity and radius of A 3+ as well as radius of O 2− , a general formula of m-o phase transition temperature (PTT) could be obtained and used to estimate PTT of A 2 Mo 3 O 12 with low relative error. Furthermore, a simple linear relationship between PTT of A 2 Mo 3 O 12 and Dr 1/4 ·De of A 3+ and Mo 6+ (radius difference Dr = r A -r Mo , electronegativity difference De = e A -e Mo ) is obtained by considering the combined influences of A 3+ and Mo 6+ . The results suggest that m-o PTT of A 2 Mo 3 O 12 should relate to the combined influences of A 3+ and Mo 6+ rather than the only influence of A 3+ .