TY - JOUR

T1 - Structure and Non-Stoichiometry of Double Sodium Molybdates with Scandium and Indium of the Alluaudite Type

AU - Solodovnikov, S. F.

AU - Savina, A. A.

AU - Solodovnikova, Z. A.

AU - Yudin, V. N.

AU - Kuchumov, B. M.

AU - Khaikina, E. G.

N1 - Publisher Copyright: © 2020, Pleiades Publishing, Ltd. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/3/1

Y1 - 2020/3/1

N2 - The structures and compositions of alluaudite-type double molybdates of sodium with scandium and indium are refined. The formulas Na5R(MoO4)4 (R = Sc, In) have previously been accepted for them, however, our new single crystal X-ray diffraction data show that their compositions noticeably differ from the initial ones: Na5.24Sc0.92(MoO4)4 = Na3.93Sc0.69(MoO4)3 (space group C2/c, Z = 4, a = 12.8911(6) Å, b = 13.9149(4) Å, c = 7.2544(3) Å, α = 113.011(2)°, R = 0.0212) and Na5.74In0.75(MoO4)4 = Na4.31In0.56(MoO4)3 (a = 12.8294(5) Å, b = 13.8906(5) Å, c = 7.2961(3) Å, β = 112.729(1)°, R = 0.0164). This indicates the nonstoichiometry of the studied crystals. Their compositions as well as initial Na5R(MoO4)4 = Na3.75R0.75(MoO4)3 are close to the opposite boundaries of homogeneity regions found near the melting points of double molybdates Na3+3xR1−x(MoO4)3 (R = Sc, In) which are 0.25 ≤ x ≤ 0.35 (R = Sc) and 0.25 ≤ x ≤ 0.45 (R = In). They are consistent with the general formula Na9−3xR1+x3+(MoO4)6 that we have previously proposed for alluaudite-type double molybdates of sodium and trivalent metals. The characteristic features of both structures are a partial occupancy of all three crystallographic sites of sodium along with the presence of the mixed octahedral site (Na, R), where R = Sc, In. The features of the crystal structures of the studied compounds, calculations of bond-valence sum maps, and also the previously obtained data of solid-state NMR and non-empirical calculations indicate the predominantly one-dimensional, as in the other alluaudites, character of the sodium ion transport through the chain of Na(3)–Na(3) polyhedra along the c axis. However, at elevated temperatures a two-dimensional conductivity is possible in the (100) plane due to the bridging positions of Na(1) and Na(2).

AB - The structures and compositions of alluaudite-type double molybdates of sodium with scandium and indium are refined. The formulas Na5R(MoO4)4 (R = Sc, In) have previously been accepted for them, however, our new single crystal X-ray diffraction data show that their compositions noticeably differ from the initial ones: Na5.24Sc0.92(MoO4)4 = Na3.93Sc0.69(MoO4)3 (space group C2/c, Z = 4, a = 12.8911(6) Å, b = 13.9149(4) Å, c = 7.2544(3) Å, α = 113.011(2)°, R = 0.0212) and Na5.74In0.75(MoO4)4 = Na4.31In0.56(MoO4)3 (a = 12.8294(5) Å, b = 13.8906(5) Å, c = 7.2961(3) Å, β = 112.729(1)°, R = 0.0164). This indicates the nonstoichiometry of the studied crystals. Their compositions as well as initial Na5R(MoO4)4 = Na3.75R0.75(MoO4)3 are close to the opposite boundaries of homogeneity regions found near the melting points of double molybdates Na3+3xR1−x(MoO4)3 (R = Sc, In) which are 0.25 ≤ x ≤ 0.35 (R = Sc) and 0.25 ≤ x ≤ 0.45 (R = In). They are consistent with the general formula Na9−3xR1+x3+(MoO4)6 that we have previously proposed for alluaudite-type double molybdates of sodium and trivalent metals. The characteristic features of both structures are a partial occupancy of all three crystallographic sites of sodium along with the presence of the mixed octahedral site (Na, R), where R = Sc, In. The features of the crystal structures of the studied compounds, calculations of bond-valence sum maps, and also the previously obtained data of solid-state NMR and non-empirical calculations indicate the predominantly one-dimensional, as in the other alluaudites, character of the sodium ion transport through the chain of Na(3)–Na(3) polyhedra along the c axis. However, at elevated temperatures a two-dimensional conductivity is possible in the (100) plane due to the bridging positions of Na(1) and Na(2).

KW - alluaudite type

KW - bond valence sum maps

KW - crystals

KW - double molybdate

KW - indium

KW - ionic conductivity

KW - nonstoichiometry

KW - scandium

KW - sodium

KW - structure

KW - synthesis

KW - non-stoichiometry

KW - CRYSTAL-STRUCTURES

KW - IONIC-CONDUCTIVITY

KW - PARAGENESIS

KW - TRANSPORT

KW - NA

KW - CHEMISTRY

KW - DIFFUSION

UR - http://www.scopus.com/inward/record.url?scp=85088663446&partnerID=8YFLogxK

U2 - 10.1134/S0022476620030087

DO - 10.1134/S0022476620030087

M3 - Article

AN - SCOPUS:85088663446

VL - 61

SP - 419

EP - 430

JO - Journal of Structural Chemistry

JF - Journal of Structural Chemistry

SN - 0022-4766

IS - 3

ER -