Metal cation effects on the structural, optical and thermal properties of double tungstates AM(WO 4 ) 2 (A = Li, Na, K; M = Y, La, Ce, Pr, Nd, Sm, Bi)

(M = La, Ce, Pr, Nd), the phase transition temperature revealed a trend for different sized rare earth elements from the low- to the high-temperature polymorphs. Moreover, MAPLE calculations were carried out for those double tungstates with single crystal data reported for the first time.