Phase relations in the Na2MoO4–Cs2MoO4 and Na2MoO4–Cs2MoO4–ZnMoO4 systems, crystal structures of Cs3Na(MoO4)2 and Cs3NaZn2(MoO4)4

Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4: different filled derivatives of the cation-deficient Cs6Zn5(MoO4)8 structure

“…The structure of proton-conductor Cs 3 Li(DSO 4 ) 4 is an example of a similar framework of the (Li 1/3 & 2/3 )O 4 and SO 4 tetrahedra (Klooster et al, 2004). We have also noted (Solodovnikov et al, 2007;Zolotova et al, 2016) that mayenite 12CaOÁ7Al 2 O 3 (Bartl & Scheller, 1970) and the related compounds 11CaOÁ7Al 2 O 3 ÁCaF 2 (Williams, 1973), wadalite Ca 6 Al 5 Si 2 O 16 Cl 3 (Tsukimura et al, 1993) and other minerals (Galuskin et al, 2015) crystallizing in the space group I43d, as well as Na 6 Zn 3 (AsO 4 ) 4 Á3H 2 O (Grey et al, 1989) and Na 6 Zn 3 (PO 4 ) 4 Á3H 2 O (Bu et al, 1997), with the space group P2 1 3, have 'polymorphous modifications' of the Cs 6 Zn 5 (MoO 4 ) 8 structure framework. In mayenite Ca 12 (O& 5 )[Al 6 (AlO 4 ) 8 ] 31 and related structures, the directions of the terminal vertices of the Al(Si)O 4 or As(P)O 4 tetrahedra along the threefold axes are opposite compared to the orientation of the MoO 4 or WO 4 tetrahedra in the Cs 6 Zn 5 (MoO 4 ) 8 family (Fig.…”

“…The metal-oxygen distances in the (Zn 2/3 Li 1/3 )O 4 tetrahedra are in good agreement with the Zn-O and Li-O bond lengths of 1.920 (4)-1.992 (5) and 1.889 (12)-2.024 (11) Å , respectively, in -LiZnPO 4 (Elammari & Elouadi, 1989) and the Zn-O bond lengths of 1.858-2.038 Å (average 1.95 Å ) in K 4 Zn(MoO 4 ) 3 (Gicquel-Mayer et al, 1980). The slightly increased Zn-O distances of 1.98-2.00 Å in Cs 6 Zn 5 (MoO 4 ) 8 (Solodovnikov et al, 1987;Mueller et al, 1987) and the (Zn,Na)-O distance of 1.987 (2) Å in Cs 3 NaZn 2 (MoO 4 ) 4 (Zolotova et al, 2016) are caused by the presence of vacancies or sodium cations in the Zn positions.…”

“…To some extent, the presence of two different environments for the alkali metal atoms in tetragonal A 3 Li 2 R(MoO 4 ) 4 (AR = TlAl, RbAl, RbGa, CsAl, CsGa, CsFe; Solodovnikov et al, 2007) elucidates reasons for the splitting of the Cs position into two sites in Cs 3 NaZn 2 (MoO 4 ) 4 (Zolotova et al, 2016). This seems to be a result of a shifting of the caesium positions caused by changes in the number and orientation of the surrounding ZnO 4 and NaO 4 tetrahedra with substantially different sizes according to the tetrahedral ionic radii of Zn 2+ and Na + , i.e.…”

“…Cs 6 Zn 5 (MoO 4 ) 8 ! Cs 3 LiZn 2 (MoO 4 ) 4 (the melting points are 783, 923 and 1003 K, respectively), where the continuous solid solutions exist with monotonic dependences of the cubic lattice parameters and melting points on the compositions (Solodovnikov et al, 2007;Zolotova et al, 2016). Inserting the lithium ions into the cation vacancies of the Cs 6 Zn 5 (MoO 4 ) 8 structure decreases its lattice parameter and increases its thermal stability 1 , whereas in the continuous solid solution Cs 6 Zn 5-x & 1-x Na 2x (MoO 4 ) 8 (0 x 1), increasing the sodium content leads to an increase of the unit-cell parameters and progressive thermal destabilization.…”

“…The search for new molybdates and tungstates of the Cs 6 Zn 5 (MoO 4 ) 8 family containing Li + and Na + cations along with Cs + or Rb + and divalent cations led us to the preparation of Cs 3 NaZn 2 (MoO 4 ) 4 (Zolotova et al, 2016) and Cs 3 LiZn 2 (WO 4 ) 4 . We also obtained single crystals of Rb 3 Li 2 Ga(MoO 4 ) 4 , whose structure is a derivative of the Cs 6 Zn 5 (MoO 4 ) 8 type as well.…”