The phase formation in the Na 2 MoO 4 -Cs 2 MoO 4 -NiMoO 4 system is studied using the solid-state synthesis and flux crystallization. The formation of a cesium-containing solid solution based on double molybdate Na 4-2 x Ni 1+ x (MoO 4 ) 3 of the alluaudite type and new triple molybdate of a related structure is established. Their structures contain layers of МоО 4 tetrahedra and coupled (Ni, Na)O 6 octahedra bridged by МоО 4 tetrahedra into three-dimensional open frameworks with tunnels along the c axis filled by sodium cations. By the example of isostructural Na 3.39 Ni 1.31 (MoO 4 ) 3 (I) and Na 3.18 Cs 0.29 Ni 1.26 (MoO 4 ) 3 (II), it is shown that in the alluaudite-type solid solution, cesium ions partially replace sodium cations in the framework tunnels, which provides the sodium ion conductivity. The structure of triple molybdate Na 2.64 Cs 0.64 Ni 1.36 (MoO 4 ) 3 (III) is a new type of the alluaudite superstructure deformed and tripled in volume. Its formation is caused by a significant differentiation of cations at (Ni, Na) and (Na, Cs) positions. In terms of the degree of deformation, this structure is intermediate between alluaudite and (pseudo)orthorhombic Na 10 Cs 4 M 5 (MoO 4 ) 12 ( M = Mn, Co) and Na 25 Cs 8 R 5 (MoO 4 ) 24 ( R = Fe, Sc, In). Among the crystallization products in the Na 2 MoO 4 -Cs 2 MoO 4 -NiMoO 4 system, crystals with a similar incommensurate modulation of the alluaudite structure along the c axis are found. Calculations of bond valence sum maps for sodium ions in the structures of I–III confirm the possibility of the one-dimensional sodium-ion conductivity for them at its lowest threshold for double molybdate for which the two-dimensional transport is also probable at elevated temperatures.

С помощью твердофазного синтеза и раствор-расплавной кристаллизации изучено фазообразование в системе Na2MoO4-Cs2MoO4-NiMoO4, установлено образование цезийсодержащего твердого раствора на основе двойного молибдата Na4-2xNi1+x(MoO4)3 типа аллюодита и нового тройного молибдата родственного строения. Их структуры содержат слои МоО4-тетраэдров и спаренных октаэдров (Ni, Na)O6, которые связаны мостиковыми МоО4-тетраэдрами в трехмерные ажурные каркасы с туннелями вдоль оси c, заполненными катионами натрия. На примере изоструктурных Na3.39Ni1.31(MoO4)3 (I) и Na3.18Cs0.29Ni1.26(MoO4)3 (II) показано, что ионы цезия в твердом растворе типа аллюодита частично замещают катионы натрия в туннелях каркаса, которые обеспечивают натрий-ионную проводимость. Структура тройного молибдата Na2.64Cs0.64Ni1.36(MoO4)3 (III) является новым типом деформированной и утроенной по объему сверхструктуры аллюодита, образование которой вызвано значительной дифференциацией катионов в позициях (Ni, Na) и (Na, Cs). Эта структура по степени деформации занимает промежуточное положение между аллюодитом и (псевдо)ромбическими Na10Cs4M5(MoO4)12 (M = Mn, Co) и Na25Cs8R5(MoO4)24 (R = Fe, Sc, In). Среди продуктов кристаллизации в системе Na2MoO4-Cs2MoO4-NiMoO4 найдены кристаллы с аналогичной несоразмерной модуляцией структуры аллюодита вдоль оси c. Расчеты карт сумм валентных усилий для ионов натрия в структурах I–III подтвердили для них возможность одномерной натрий-ионной проводимости при наиболее низком ее пороге у двойного молибдата, для которого при повышенных температурах вероятен и двухмерный транспорт.

The work reviews the structure, non-stoichiometry, and ionic mobility of molybdates, tungstates, and other compounds crystallizing in the structure type of alluaudite (Na, Ca)(Fe, Mn, Mg)3(PO4)3 with the general Moore′s crystal chemical formula X(2)X(1)M(1)M(2)2(TO4)3, where X are large cations Na+, Ca2+, K+, Pb2+, etc., with the coordination number 8; M are octahedral cations, T = P, As, V, S, Mo, W. Using this formula and the corresponding site occupancies, possible limits of double molybdate and tungstate compositions of the alluaudite family are determined. Various types of distortions (superstructures) of alluaudite are considered; several groups of phases with different symmetries, numbers of anions in the unit cell, and vector relations with the unit cell of the original alluaudite structure are distinguished. It is shown that chains of partially defective positions X(2) and X(1) aligned along axis c play a key role in the transport of sodium cations in the alluaudite type phases. Phosphates and sulfates with alluaudite structure exhibit mainly 1D transport of sodium ions; however, calculations of the bond-valence sum maps, NMR data, and ab initio calculations show that 2D transport in the (100) plane is possible in complex molybdates and tungstates due to the transport of Na+ ions between X(2)–X(2) and X(1)–X(1) channels through the bridging site M(1). It is shown that the family of alluaudite-related (pseudo)orthorhombic triple molybdates Na10Cs4M5(MoO4)12 (M = Mn, Co) and Na25Cs8R5(MoO4)24 (R = Fe, Sc, In) also exhibits 2D diffusion of sodium ions via successive zigzag ion hoppings and that 3D transport may appear at elevated temperatures.

Рассмотрены особенности строения, нестехиометрия и ионная подвижность молибдатов, вольфраматов и других соединений, кристаллизующихся в структурном типе аллюодита (Na, Ca)(Fe, Mn, Mg)3(PO4)3 с общей кристаллохимической формулой по П. Муру X(2)X(1)M(1)M(2)2(TO4)3, где X — крупные катионы Na+, Ca2+, K+, Pb2+ и др. с КЧ = 8; M — октаэдрические катионы, T = P, As, V, S, Mo, W. На основе этой формулы и заселенностей соответствующих позиций выведены возможные пределы составов двойных молибдатов и вольфраматов типа аллюодита. Рассмотрены виды искажения (сверхструктуры) аллюодита, выделено несколько групп фаз, различающихся симметрией, числом анионов в ячейке и векторной связью с ячейкой исходной структуры аллюодита. Показано, что ключевую роль в переносе катионов натрия в фазах типа аллюодита играют цепочки частично дефектных позиций X(2) и X(1), идущие вдоль оси c. Для фосфатов и сульфатов со структурой аллюодита характерен преимущественно одномерный транспорт ионов натрия, однако, согласно данным расчетов карт сумм валентных усилий, ЯМР спектроскопии и ab initio расчетов, в сложных молибдатах и вольфраматах есть возможность двухмерной проводимости в плоскости (100) за счет перетока ионов Na+ между каналами X(2)—X(2) и X(1)—X(1) через мостиковую позицию M(1). Показано, что в семействе родственных аллюодиту (псевдо)ромбических тройных молибдатов Na10Cs4M5(MoO4)12 (M = Mn, Co) и Na25Cs8R5(MoO4)24 (R = Fe, Sc, In) также возможна двухмерная диффузия ионов натрия через последовательные зигзагообразные ионные перескоки с вероятной реализацией трехмерного транспорта при повышенных температурах.

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 $$\text{Na}_{9-3x}R_{1+x}^{3+}(\text{MoO}_4)_6$$ 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).

Уточнены структуры и составы двойных молибдатов натрия со скандием и индием типа аллюодита. для них приняты формулы Na5R(MoO4)4 (R = Sc, In), однако наши новые монокристалльные данные показывают, что их составы заметно отличаются от первоначальных: Na5.24Sc0.92(MoO4)4 = Na3.93Sc0.69(MoO4)3 (пр. гр. C2/c, Z = 4, a = 12.8911(6) Å, b = 13.9149(4) Å, c = 7.2544(3) Å, β = 113.011(2)°, R = 0.0212) и 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). Это свидетельствует о нестехиометрии изученных кристаллов. Их составы, а также исходные Na5R(MoO4)4 = Na3.75R0.75(MoO4)3 близки к противоположным границам, найденным вблизи точек плавления областей гомогенности двойных молибдатов Na3+3xR1–x(MoO4)3 (R = Sc, In), которые составляют 0.25 ≤ x ≤ 0.35 (R = Sc) и 0.25 ≤ x ≤ 0.45 (R = In) и согласуются с общей формулой Na9–3xR1+x3+(MoO4)6 (Z = 2), предложенной нами ранее для двойных молибдатов натрия и трехвалентных металлов типа аллюодита. Характерными чертами обеих структур является частичное заселение всех трех кристаллографических позиций натрия наряду с наличием смешанной октаэдрической позиции (Na, R), где R = Sc, In. Особенности кристаллических структур изученных соединений, расчеты карт сумм валентных усилий, а также полученные ранее данные твердотельного ЯМР и неэмпирических расчетов свидетельствуют о преимущественно одномерном, как и у других аллюодитов, характере натрий-ионного транспорта по цепочке полиэдров Na(3)—Na(3) вдоль оси c, однако при повышенных температурах за счет мостиковых позиций Na(1) и Na(2) возможна двумерная проводимость в плоскости (100).

Исследовано замещение молибдена на вольфрам в димолибдате цезия Cs2Mo2O7 с образованием твердого раствора α-Cs2Mo2–xWxO7 и найдено, что его область гомогенности при 540 °C достигает 0 ≤ x ≤ 0.6. Установлено, что объем моноклинной (псевдоромбической) элементарной ячейки и температура плавления твердого раствора монотонно возрастают с ростом содержания вольфрама, тогда как температура фазового перехода в ромбическую фазу практически неизменна и составляет около 390 °C. Получены кристаллы твердых растворов нескольких составов, определено их строение и найдено, что атомы вольфрама в основном локализованы в октаэдрических позициях структуры α-Cs2Mo2O7. Электропроводность Cs2Mo2O7 возрастает примерно на два порядка в результате фазового перехода при температуре 390 °C, достигая значения 1.2⋅10–4 См/см при 460 °C. Ввиду больших размеров ионов Cs+ и высокого заряда катионов молибдена предполагается, что переносчиком заряда являются анионы кислорода. Расчет карт сумм валентных усилий (СВУ) для возможных положений атомов кислорода в ячейке α-Cs2Mo2O7 показывает образование трехмерной системы каналов кислородной проводимости при значениях граничных изоповерхностей СВУ ≥ 2.13.

The tungsten substitution for molybdenum in cesium dimolybdate Cs2Mo2O7 with the formation of an α-Cs2Mo2−xWxO7 solid solution is studied, and its homogeneity region at 540 °C is found to reach 0 ≤ x ≤ 0.6. It is established that the volume of the monoclinic (pseudo-orthorhombic) unit cell and the solid solution melting point monotonically increase with increasing tungsten content, whereas the phase transition temperature to the orthorhombic phase remains practically constant and is ∼390 °C. The crystals of solid solutions with several compositions are obtained, their structure is determined, and the tungsten atoms are found to be mainly located in octahedral positions of the α-Cs2Mo2O7 structure. As a result of the phase transition at 390 °C the electrical conductivity of Cs2Mo2O7 increases approximately by two orders of magnitude reaching 1.2·10−4S/cm at 460 °C. Due to a large size of Cs+ ions and a high charge of molybdenum cations it is supposed that the charge carriers are oxygen anions. The calculation of bond valence sum (BVS) maps for possible positions of oxygen atoms in the α-Cs2Mo2O7 cell shows the formation of a 3D system of oxygen conductivity channels at boundary BVS isosurface values ≥ 2.13.

New ternary molybdate Cs2NaBi(MoO4)3 is synthesized in the system Na2MoO4–Cs2MoO4–Bi2(MoO4)3. The structure of Cs2NaBi(MoO4)3 of a new type is determined in noncentrosymmetric space group R3c, a=10.6435(2), c=40.9524(7)Å, V=4017.71(13)Å3, Z=12 in anisotropic approximation for all atoms taking into account racemic twinning. The structure is completely ordered, Mo atoms are tetrahedrally coordinated, Bi(1) and Bi(2) atoms are in octahedra, and Na(1) and Na(2) atoms have a distorted trigonal prismatic coordination. The Cs(1) and Cs(2) atoms are in the framework cavities with coordination numbers 12 and 10, respectively. No phase transitions were found in Cs2NaBi(MoO4)3 up to the melting point at 826K. The compound shows an SHG signal, I2w/I2w(SiO2)=5 estimated by the powder method. The vibrational properties are evaluated by Raman spectroscopy, and 26 narrow lines are measured.

The review summarizes experimental data on the phase formation, structure and properties of new complex oxide compounds group – triple molybdates containing tetrahedral molybdate ion, two different singly charged cation, together with tri- or divalent cation. The several structural families of these compounds were distinguished and it shown that many of them are of interest as luminescent, laser, ion-conducting or nonlinear optical materials.

In the samples of the Na2MoO4-MgMoO4 system quenched in the air at above 600°C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na4−2x Mg1+x (MoO4)3 (0.05 ≤ x ≤ 0.35) and triclinic Na2−2y Mg2+y (MoO4)3 (0.10 ≤ y ≤ 0.40) isostructural to previously studied Na2Mg5(MoO4)6. Sodium-magnesium molybdate of the Li3Fe(MoO4)3 structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na2Mg5(MoO4)6 structure type (space group \(P\bar 1\), Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)0.5(Na0.255□0.745)(Na0.755Mg0.245)Mg2(MoO4)3 or Na1.51Mg2.245(MoO4)3 (a = 6.9577(1) Å, b = 8.6330(2) Å, c = 10.2571(2) Å, α = 106.933(1)°, β = 104.864(1)°, γ = 103.453(1)°, R = 0.0188); for the compound with manganese (Na)0.5(Na0.33□0.67)(Na0.83Mn0.17)Mn2(MoO4)3 or Na1.64Mn2.17(MoO4)3 (a = 7.0778(2) Å, b = 8.8115(2) Å, c = 10.4256(2) Å, α = 106.521(1)°, β = 105.639(3)°, Γ = 103.233(1)°, R = 0.0175). The Na2Mg5(MoO4)6 structure is redetermined and it is shown that actually it corresponds to the composition Na1.40Mg2.30(MoO4)3.

In the samples of the Na2MoO4-MgMoO4 system quenched in the air at above 600A degrees C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na4-2x Mg1+x (MoO4)(3) (0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.35) and triclinic Na2-2y Mg2+y (MoO4)(3) (0.10 a parts per thousand currency sign y a parts per thousand currency sign 0.40) isostructural to previously studied Na2Mg5(MoO4)(6). Sodium-magnesium molybdate of the Li3Fe(MoO4)(3) structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na2Mg5(MoO4)(6) structure type (space group , Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)(0.5)(Na(0.255)a-(0.745))(Na0.755Mg0.245)Mg-2(MoO4)(3) or Na1.51Mg2.245(MoO4)(3) (a = 6.9577(1) , b = 8.6330(2) , c = 10.2571(2) , alpha = 106.933(1)A degrees, beta = 104.864(1)A degrees, gamma = 103.453(1)A degrees, R = 0.0188); for the compound with manganese (Na)(0.5)(Na(0.33)a-(0.67))(Na0.83Mn0.17)Mn-2(MoO4)(3) or Na1.64Mn2.17(MoO4)(3) (a = 7.0778(2) , b = 8.8115(2) , c = 10.4256(2) , alpha = 106.521(1)A degrees, beta = 105.639(3)A degrees, I" = 103.233(1)A degrees, R = 0.0175). The Na2Mg5(MoO4)(6) structure is redetermined and it is shown that actually it corresponds to the composition Na1.40Mg2.30(MoO4)(3).

A subsolidus triangulation of Li 2 MoO 4 -Rb 2 MoO 4 -MMoO 4 (M = Ca, Sr, Pb, Ba) systems is performed. The RbLiMoO 4 -Rb 2 M(MoO 4 ) 2 (M = Pb, Ba) joins, where 11 mol.% long Rb 2 M(MoO 4 ) 2 -based solid solutions are found, are studied in most detail. Ternary molybdates do not form in the systems, which is confirmed by spontaneous flux crystallization. The α-Rb 2 Pb(MoO 4 ) 2 crystals are obtained and their crystal structure is solved ( a = 20.9724(15) Å, b = 12.1261(8) Å, c = 16.1171(10) Å, β = 115.728(13)°, C 2/ m space group, R = 0.0695, Z = 16), which is a monoclinic superstructure of the palmierite type and has the largest cell volume and the most complex structure among lead-containing palmierites. One of the MoO 6 tetrahedra is orientationally disordered over two sites; lead atoms are shifted from the centers of their coordination polyhedra to one of their faces and have cn = 6–8; for rubidium cations cn = 10–12.

A subsolidus triangulation of Li2MoO4-Rb2MoO4-MMoO4 (M = Ca, Sr, Pb, Ba) systems is performed. The RbLiMoO4-Rb2M(MoO4)2 (M = Pb, Ba) joins, where 11 mol.% long Rb2M(MoO4)2-based solid solutions are found, are studied in most detail. Ternary molybdates do not form in the systems, which is confirmed by spontaneous flux crystallization. The α-Rb2Pb(MoO4)2 crystals are obtained and their crystal structure is solved (a = 20.9724(15) Å, b = 12.1261(8) Å, c = 16.1171(10) Å, β = 115.728(13)°, C2/m space group, R = 0.0695, Z = 16), which is a monoclinic superstructure of the palmierite type and has the largest cell volume and the most complex structure among lead-containing palmierites. One of the MoO6 tetrahedra is orientationally disordered over two sites; lead atoms are shifted from the centers of their coordination polyhedra to one of their faces and have cn = 6–8; for rubidium cations cn = 10–12.

The subsolidus regions of the Li2MoO4-A 2 + MoO4-NiMoO4 (A+ = K, Rb, Cs) systems at 510°C have been triangulated by the intersecting-joins method. The A2MoO4-Li2Ni2(MoO4)3, Li2MoO4-A2Ni2(MoO4)3, A2Ni2(MoO4)3-Li2Ni2(MoO4)3 (A = K, Rb, Cs), and ALiMoO4-A2Ni2(MoO4)3 (A = K, Rb) joins have been investigated. The subsolidus phase formation study has also been completed by spontaneous flux crystallization. No triple salts have been identified, but only compounds belonging to the boundary binary systems. The crystal structure of Cs2Ni2(MoO4)3 (a = 10.7538 Å, Z = 4, space group P213, R = 0.0082) belonging to the langbeinite type has been determined. It is built of a three-dimensional framework of vertexsharing MoO4 tetrahedra and NiO6 octahedra and cesium ions occupying large out-of-framework cavities. All alkali-metal nickel molybdates are yellow. These compounds are usable as pigments, as judged from their reflection spectra and calculated color characteristics, namely, colorfulness (C), lightness (L), and hue (H).

Based on the corrected phase diagrams proper growth conditions for Li2Zn2(MoO 4 ) 3 crystals are selected. Large crystals (up to 100 mm), both impurity-free and activated by transition metal ions (Cu, Cr), are grown by the low-gradient Czochralski method. By the EPR method the charge state and structural position of copper and chromium ions are determined. The performed studies of luminescent properties show that for impurity-free crystals luminescence with λ = 388 nm with a two-exponential luminescence decay with τ 1 = 2 ns and τ 2 = 6 ns is observed at room temperature. At 77 K for both impurity-free crystals and those activated with transition metal ions luminescence with λ = 560 nm and the luminescence lifetime τ = 100 ns is observed, the intensity of luminescence with λ = 560 nm depending on the nature and concentration of transition metal ions. Cation vacancies responsible for the charge compensation of impurity transition metal ions are assumed to be also responsible for low-temperature luminescence.

The optimal conditions for Li2Zn2(MoO4)(3) crystal growth were selected on the basis of corrected phase diagram. Large undoped and activated by transition metal ions (Cu, Cr, Fe, Ti) crystals were grown upon these conditions. Charge state and structural position of transition metal ions were determined by EPR method. Investigations of luminescence shown that the luminescence with lambda = 388 nm is observed for undoped crystals at room temperature. The luminescence lifetime is described by two exponential components, with relaxation times tau(1) = 2 ns and tau(2) = 6 ns. The luminescence with lambda = 560 nm and lifetime tau = 100 nm is observed as for undoped, so as for activated by transition metal ions crystals at 77 K. Besides, the luminescence intensity with lambda = 560 nm depends on nature and concentration of transition metal ions. It is supposed, that cation vacancies, which ensure the charge compensation of the impurity transition metal ions, are responsible for the low-temperature luminescence.

Solid-phase interactions in Li 2 MoO 4 -K 2 MoO 4 -MMoO 4 (M = Ca, Pb, Ba) systems were studied, and the subsolidus regions of these systems were triangulated. The lead and barium systems were studied in a more detailed way to discover that, along KLiMoO 4 -K 2 M(MoO 4 ) 2 (M = Pb, Ba), KLiMoO 4 -PbMoO 4 , and Li 2 MoO 4 -K 2 Ba(MoO 4 ) 2 quasi-binary sections, there are homogeneity regions reaching 6–11 mol % based on K 2 M(MoO 4 ) 2 and lead molybdate. Triple molybdates are formed in none of the systems, which is verified by experiments on spontaneous crystallization from solution in melt. Crystallization experiments yielded crystals of potassium dimolybdate and simple and double molybdates from the boundary systems. The crystal structure was solved for a hexagonal KLiMoO 4 phase: (Na,K){ZnPO4}, a = 18.8838(7) Å, c = 8.9911(6)Å, Z = 24, space group P 6 3 , R = 0.065. The structure comprises a three-dimensional tridymite framework built by an alternation of corner-sharing LiO 4 - and MoO 4 tetrahedra wherein voids are occupied by potassium cations.

Subsolidus phase relations in the Cs2MoO4-MMoO4-Zr(MoO4)2 (M = Mn, Zn) ternary systems were determined, and two groups of new isostructural triple molybdates were synthesized: Cs2MZr(MoO4)4 and Cs2MZr2(MoO4)6 (M = Mn, Mg, Co, Zn). Cs2MnZr2(MoO4)6 and Cs2MnZr(MoO4)4 crystals were grown by spontaneous flux crystallization and used in structure solution for both groups of compounds. The Cs2MnZr2(MoO4)6 structure (a =13.4322(2) Å, c = 12.2016(3) Å, group R3, Z = 3, R = 0.0367) is a new structure type characterized by a mixed three-dimensional framework built of corner-sharing MoO4 tetrahedra and (M, Zr)O6 octahedra where large channels are occupied by cesium cations. Cs2MnZr2(MoO4)4 (a =5.3890(1) Å, c = 8.0685(3) Å, space group P \(\bar 3\) m1, Z = 0.5, R = 0.0247) has the layered glaserite-like KAl(MoO4)2 type structure, where Al3+ octahedral positions are randomly occupied by a 0.5M2+ + 0.5Zr4+ mixture.

Subsolidus phase relations in the Ag 2 MoO 4 -CuO-MoO 3 oxide-salt ternary system were determined. T-x diagram was plotted for the Ag 2 MoO 4 -CuMoO 4 quasi-binary join. Double molybdate Ag 2 Cu 2 (MoO 4 ) 3 was found to exist on this join. This compound is a superstructure derived from orthorhombic Li 3 Fe(MoO 4 ) 3 . Its structure was solved in terms of a subcell ( a = 5.0749(3), b = 11.300(2), c = 18.127(3) Å, space group Pnma , Z = 4, R = 0.0678). In the true unit cell, the parameter a is tripled; suggested space group is P 2 1 2 1 2 1 . A characteristic feature of the Ag 2 Cu 2 (MoO 4 ) 3 structure is infinite columns (extended along axis a ) of face-sharing oxygen octahedra, in which disordered silver atoms are located (Ag(21), Ag(22), and Ag(23)) with various degrees of irregularity of their octahedral coordination and a strong anisotropy of thermal vibrations. Distorted CuO 6 octahedra form zigzag ribbons extended in the same direction. MoO 4 tetrahedra, which are arranged according to the pseudo-hexagonal law, link the aforementioned major structural elements into a three-dimensional framework. Trigonal-prismatic voids of the framework are occupied by silver atoms Ag (1). Presumably, the disorder of the silver ions in octahedral columns can be responsible for the increased ion conductivity of silver copper molybdate. A partial order of the same ions is the most likely reason for the appearance of superstructure with the tripled unit cell volume.