“…However, compared with the large group of double tungstates (see, for example, Klevtsov & Klevtsova, 1977;Evdokimov et al, 1991), there exist only a few triple and more complex tungstates Li 3 Ba 2 R 3 (WO 4 ) 8 (R = La, Eu, Gd, Ho, Y) (Li et al, 2009(Li et al, , 2010(Li et al, , 2012Pan et al, 2012;Xiao et al, 2012b;Zeng et al, 2013;Hu et al, 2016;Guo et al, 2018) and Li 3 BaSrLa 3 (WO 4 ) 8 (Wei et al, 2015;Singh & Vaidyanathan, 2017), being filled derivatives of the BaNd 2 (MoO 4 ) 4 type (Kiseleva et al, 1979) and scheelite-like KBaLn(WO 4 ) 3 (Ln = Eu, Gd) (Xiao et al, 2012a;Wang et al, 2017), which are considered as promising laser hosts and phosphors for white LEDs. Recently we prepared a triple tungstate containing no trivalent metals, Cs 3 LiZn 2 (WO 4 ) 4 (Solodovnikov et al, 2017) which is a filled variant of the cation-deficient Cs 6 Zn 5 (MoO 4 ) 8 structure (Solodovnikov et al, 1987), and revealed a new group of silver-ion conducting triple tungstates Ag 1Àx Mg 1Àx R 1+x (WO 4 ) 3 (R = Sc, Al; 0-0.3 x 0.5) of the NASICON type (Kotova et al, 2016).…”