Synthesis, crystal structure and electrophysical properties of triple molybdates containing silver, gallium and divalent metals 132 D O I: 1 0. 15 82 6/ ch im te ch .2 01 8. 5. 3. 02 Kotova I. Yu., Savina A. A., Vandysheva A. I., Belov D. A., Stefanovich S. Yu. Chimica Techno Acta. 2018. Vol. 5, No. 3. P. 132–143. ISSN 2409–5613 I. Yu. Kotovaa, A. A. Savinaa*, A. I. Vandyshevab, D. A. Belovc, S. Yu. Stefanovichc aBaikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, 6 Sakh’yanova St., Ulan-Ude, 670047, Buryat Republic, Russian Federation bBuryat State University, 24a Smolin St., Ulan-Ude, 670000, Buryat Republic, Russian Federation cLomonosov Moscow State University, Leninskie Gory, 1, Moscow 119991, Russian Federation *E-mail: alex551112@mail.ru Synthesis, crystal structure and electrophysical properties of triple molybdates containing silver, gallium and divalent metals A possibility of the triple molybdates formation with both NASICON-like and NaMg3In(MoO4)5 structures in the Ag2MoO4–AMoO4–Ga2(MoO4)3 (A = Mn, Co, Zn, Ni) systems was studied by powder X-ray diffraction analysis. It was established that NASICON-like phases Ag1−xA1−xGa1+x(MoO4)3 are not formed. The triple molyb- dates AgA3Ga (MoO4)5 (A = Mn, Co, Zn) isostructural to triclinic NaMg3In(MoO4)5 (sp. gr. P1, Z = 2) were synthesized and characterized. The structure of the obtained compounds was refined for AgZn3Ga(MoO4)5 according to the powder data by the Rietveld method. The structure consists of MoO4 tetrahedra, couples of edge-shared M(1)O6 octahedra, and trimers of edge-shared M(2)O6–, M(3)6– and M(4)O6 octahedra, which are linked by the common vertices to form a 3D framework. High-temperature conductivity measurements revealed that the conductivity of AgMn3Ga(MoO4)5 at 500 °С reaches 10–2 S / cm, which is close to one of the known NASICON-type ionic conductors. Keywords: triple molybdates; silver; gallium; solid-state synthesis; powder X-ray diffraction; Rietveld refinement; ionic conductivity. Received: 10.10.2018. Accepted: 22.10.2018. Published: 31.10.2018. © Kotova I. Yu., Savina A. A., Vandysheva A. I., Belov D. A., Stefanovich S. Yu., 2018 Introduction A synthesis and studying of com- plex oxide compounds, the development of  new materials with functionally sig- nificant properties based on  those are among the main areas of  the materials science. An important place in the study and obtaining of new phases with valuable physicochemical properties belongs to mo- lybdates, in particular triple ones, which are among the fastest-growing groups of complex oxide compounds containing a  tetrahedral anion and three different cations. One of the largest families of these compounds is molybdates containing 1-, 2- and 3-charged cations. In particular, silver-containing NASICON-like phases 133 Ag1–xA1–xR1+x(MoO4)3 (A = Mg Co, R = Al; A = Mg, R = In) with different homoge- neity range and triclinic AgA3R(MoO4)5 (A = Mg, R = Cr, Fe, Ga; A = Mn, R = Al, Cr, Fe, Sc, In) having high ionic conduc- tivity (10–3–10–2 S / cm) are of interest. For a  number of  phases: AgMg3R(MoO4)5 (R  = Cr, Fe), AgMnII3 (Mn III 0.26Al0.74) (MoO4)5, Ag0.90Al1.06Co2.94(MoO4)5 and AgFeII3Fe III(MoO4)5 single crystals were obtained and their crystal structures were determined [1–9]. The purpose of  this work is to  study the possibility of  forming triple mo- lybdates Ag1–xA1–xGa1+x(MoO4)3 and AgA3Ga(MoO4)5 (A = Mn, Co, Zn, Ni) and investigate crystal structure and electro- physical properties of the obtained com- pounds. Experimental The initial materials were simple mo- lybdates of silver, manganese, cobalt, zinc, nickel, MoO3 and Ga2O3 (reagent grade). Ag2MoO4 and molybdates of divalent metals were obtained by the step annealing of stoichiometric mixtures of AgNO3 (ana- lytical grade), MnO, Co(NO3)2·6H2O, ZnO, MoO3 (all chemically pure), NiO (reagent grade) at 350−450 °С (Ag2MoO4), 400−750 °С (MnMoO4), 300−700 °С (CoMoO4), 500−700 °С (ZnMoO 4), 450−750 °С (NiMoO4) in  the air with intermittent grindings every 15 hours for better sample homogenization. Power X-ray diffraction (PXRD) patterns of the prepared compounds do not contain reflec- tions of starting or impurity phases. PXRD and thermal characteristics of all prepared compounds agree well with corresponding data reported in [10−15]. Sample compositions Ag1–xA1–xGa1+x (MoO4)3 (0 ≤ x ≤ 0.7, Δx = 0.1) and AgA3Ga(MoO4)5 were prepared by  the annealing of  appropriate stoichiometric mixtures of Ag2MoO4, АMoO4, MoO3 and Ga2O3. The initial mixtures were annealed starting at 300 °C followed by raising the temperature by 20–50 °C (in some cases, 5–10 °C) with intermittent grindings every 20–30 hours for sample homogenization. The calcination time at each temperature was 30–70 h. The phase composition of the obtained products was controlled by the PXRD analysis before each increasing of the annealing temperature. PXRD patterns were collected at room temperature on a Bruker D8 ADVANCE diffractometer using Cu Kα radiation in the 2θ range from 5° to 100° with a step of 0.02076°. Possible impurity phases were checked by comparing their PXRD patterns with those in the Powder Diffraction File. The crystal structure refinement was car- ried out with the GSAS [16] program suite using PXRD data. Lattice parameters and individual scale factors were established, and five common peak-shape parameters of the pseudo-Voigt function (No. 2), one asymmetry parameter and one parameter for  the zero-point correction were used to describe the powder patterns. The back- ground level was described by a combina- tion of 15-order Chebyshev polynomials. Isotropic displacement parameters (Uiso) were refined, and grouped by  chemical similarity by used constrains. Thermoanalytic studies were carried out on  a  STA 449 F1 Jupiter NETZSCH thermoanalyser (Pt crucible, heating rate of 10 °С / min in Ar stream). Ceramic disks for  dielectric investi- gations were prepared by the calcination of  pressed powder at  600 °С  for  2 h. The disks were of  9–10 mm in  diameter and 134 1–2 mm thick, the electrodes were depo- sited by painting the disk bases with col- loid platinum followed by subsequent one hour annealing at  about 580 °С.  The di- rect current (DC) electric conductivity was measured with a  V7–38 microammeter. To study the ion transfer, electrical con- ductivity was measured on an alternating current (AC) by the two-contact method in the frequency range 1 Hz–1 MHz in the temperature range 25–560 °C at  the rate of 4 °C / min at both heating and cooling using a  Novocontrol Beta-N impedance analyzer. The activation energy of electrical conductivity was calculated from the slope of the straight lines corresponding to the Arrhenius dependence in lg (σT) – (103 / T) coordinates. Results and discussion PXRD characteristics The presence of NASICON-like phases in the Ag2MoO4–AMoO4–Ga2(MoO4)3 sys- tems was determined according to PXRD analysis of samples Ag1−xA1−xGa1+x(MoO4)3 (0 ≤ x ≤ 0.7, Δх = 0.1) which were annealed in  the temperature range from 300 °C to melting point. The final annealed tem- perature was 550–700 °C and depended on both the composition of the reaction mixtures and the nature of  the divalent metal. It was established that, despite the close values of  the Al3+ (0.53) and Ga3+ (0.62 Å [17]) radii, gallium containing triple molybdates with NASICON-like structure, apparently, do not exist. All our attempts to obtain rhombohedral phases Ag1−xA1−xGa1+x(MoO4)3 by solid state syn- thesis did not lead to  a  positive result, probably this is due to the low reactivity of gallium in the molybdate systems. Thus, the simple gallium molybdate Ga2(MoO4)3 has not yet been obtained by  ceramic techno logy, and only recently it was syn- thesized by the sol-gel method [18]. Be- sides, silver-gallium double molybdate is not synthesized either by  ceramic tech- nology or by co-precipitation. In [19] this compound was obtained by the calcining of mixtures of AgNO3, Ga2O3, MoO3 (in ra- tio 2:1:4) at  350–400 °C for  8–10 h, fol- lowed by cooling, homogenization, and the repeated 12–20 hours annealing at  500– 550 °C, but the PXRD data of the product are not given by the authors. It should be noted that in none of the later publications (including those of the same authors) ad- ditional information about this compound was found. At the same time, in  the Ag2MoO4– AMoO4–Ga2(MoO4)3 systems triple mo- lybdates of composition AgA3Ga(MoO4)5 were found. These compounds were syn- thesized by the solid-state reactions at 550– 600 °С  (A = Mn), 540–550 °С  (A  =  Zn), 500–530 °С (A = Co) for 80–100 h. How- ever, nickel-containing compound was not obtained in the single-phase state, even after sintering at temperatures as high as 600– 650 °C for 250–300 hours. This may be due to the smallest radius of Ni2+ cation (0.69 Å for  CN = 6 [17]) in  the studied series of simple molybdates of divalent metals. The triple molybdates AgA3Ga(MoO4)5 (A = Zn, Mn, Co) were found to melt in- congruently at temperatures of 644, 727, and 739 °C, respectively. The powder XRD patterns of  as- prepared single-phase compounds AgA3Ga(MoO4)5 are similar and show that these oxides are isostructural to triclinic NaMg3In(MoO4)5 (sp. gr. P1, Z = 2) [20]. The diffractograms of the AgA3Ga(MoO4)5 (A = Mn, Co, Zn) were indexed with tak- ing into account our data obtained earlier in the course of single-crystal structure de- 135 termination of AgMg3R(MoO4)5, R = Fe, Cr [7]. The result of indexing the PXRD patterns for  AgA3Ga (MoO4)5 (A = Mn, Co, Zn) are given in Table 1. Unit-cell para- meters are listed in Table 2. Crystal structure of AgZn3Ga(MoO4)5 T h e c r y s t a l s t r u c t u r e of  AgZn3Ga(MoO4)5 was refined ac- cording to  the Rietveld method [21], starting with the atomic coordinates of AgMg3Fe(MoO4)5 structure [7]. Crystal data, data collection and structure refine- ment details are summarized in Table 3. Experimental, theoretical, and difference PXRD patterns for the AgZn3Ga(MoO4)5 are shown in  Figure 1. The fractional Table 1 The calculated and observed values of PXRD data for AgA3Ga(MoO4)5 (A = Mn, Zn, Co) h k l AgMn3Ga(MoO4)5 AgZn3Ga(MoO4)5 AgCo3Ga(MoO4)5 I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° 0 0 2 3 9.861 9.850 2 9.981 9.991 2 10.006 10.019 0 1 0 1 12.782 12.767 1 12.954 12.945 1L 12.956 12.943 1 0 0 9 12.903 12.894 9 13.058 13.064 9 13.112 13.108 0 1 1 1L 13.769 13.750 1 0 1 1L 13.654 13.637 1 13.778 13.808 1L 13.853 13.849 0 –1 1 1L 14.021 13.998 1L 14.005 14.017 –1 0 1 1L 13.974 13.977 2 14.170 14.175 1 14.231 14.226 0 0 3 1L 14.805 14.798 1 15.010 15.011 1L 15.061 15.052 1 0 2 1 15.924 15.959 1L 16.154 16.157 1 16.177 16.200 0 –1 2 1L 16.388 16.393 1L 16.577 16.576 1 16.625 16.619 –1 0 2 1L 16.529 16.538 1L 16.799 16.783 1L 16.819 16.844 1 1 1 1L 17.079 17.075 –1 –1 1 1L 17.541 17.562 1L 17.596 17.610 1 1 2 1L 18.728 18.728 1 0 3 1L 19.304 19.310 –1 –1 2 2 19.638 19.630 3 19.826 19.822 3 19.892 19.891 0 0 4 1 19.780 19.774 1L 20.127 20.115 –1 1 0 19.792 1L 20.115 20.122 20.154 –1 0 3 1L 20.025 20.033 1L 20.340 20.336 –1 1 1 1L 20.406 20.425 1L 20.774 20.790 1L 20.819 20.817 1 1 3 3 21.572 21.577 4 21.846 21.856 5 21.861 21.864 1 –1 2 6 22.117 22.117 10 22.419 22.427 10 22.483 22.482 –1 –1 3 1 22.959 22.996 1L 23.048 23.085 1 0 4 3 23.267 23.270 3 23.569 23.573 3 23.646 23.631 0 1 4 23.265 2 23.662 23.668 1 23.695 23.675 0 –1 4 1 23.959 23.944 10 24.193 24.222 3 24.313 24.306 –1 0 4 1 24.086 24.078 2 24.441 24.445 1 24.511 24.529 0 0 5 100 24.793 24.787 100 25.145 25.148 86 25.221 25.218 –1 1 3 6 24.869 24.848 16 25.307 25.312 16 25.344 25.346 136 h k l AgMn3Ga(MoO4)5 AgZn3Ga(MoO4)5 AgCo3Ga(MoO4)5 I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° 1 1 4 3 25.122 25.119 5 25.459 25.465 6 25.480 25.478 0 2 0 3 25.701 25.697 2 26.072 26.058 2 26.055 26.054 2 0 0 73 25.959 29.954 83 26.307 26.302 100 26.396 26.392 0 2 1 23 26.036 26.025 38 26.417 26.422 26.403 2 0 1 10 26.255 26.250 20 26.596 26.590 18 26.679 26.676 0 –2 1 6 26.337 26.333 22 26.664 26.674 7 26.697 26.690 –1 –1 4 4 26.483 26.488 7 26.780 26.782 7 26.888 26.890 1 2 0 8 26.613 26.601 3 26.883 26.881 26.892 –2 0 1 26.614 7 26.984 26.984 7 27.079 27.081 1 2 1 11 26.835 26.829 25 27.132 27.137 18 27.133 27.131 2 1 1 2 27.007 27.001 5 27.283 27.278 3 27.350 27.345 –1 –2 1 11 27.307 27.306 26 27.575 27.575 19 27.613 27.609 0 2 2 27.285 4 27.712 27.731 3 27.705 27.703 –2 –1 1 3 27.507 27.503 4 27.790 27.784 3 27.880 27.879 0 1 5 6 27.622 27.611 10 28.081 28.084 8 28.109 28.105 0 –2 2 3 27.874 27.873 6 28.208 28.210 5 28.255 28.250 1 2 2 2 27.961 27.970 4 28.320 28.322 4 28.308 28.304 1 –1 4 2 28.066 28.064 6 28.423 28.425 5 28.512 28.510 2 1 2 2 28.114 28.121 28.423 3 28.454 28.481 –2 0 2 2 28.164 28.167 1 28.567 28.573 2 28.672 28.678 0 –1 5 6 28.342 28.336 16 28.678 28.676 13 28.782 28.778 –1 0 5 1 28.893 28.900 1 29.000 28.997 –1 –2 2 1 28.877 28.882 2 29.163 29.159 1 29.223 29.217 –2 –1 2 4 29.081 29.082 10 29.391 29.390 9 29.499 29.501 0 2 3 3 29.376 29.367 4 29.859 29.869 3 29.837 29.839 2 0 3 1L 29.525 29.516 2 29.898 29.888 1 29.985 29.973 0 0 6 1 29.860 29.850 1 30.300 30.287 1 30.383 30.372 1 2 3 1L 29.929 29.927 1 30.365 30.334 1 30.324 30.310 2 1 3 4 30.055 30.056 9 30.397 30.397 9 30.453 30.450 0 –2 3 1L 30.175 30.189 1 30.527 30.539 1 30.590 30.603 –2 0 3 1L 30.513 30.488 1 30.983 30.940 1L 31.055 31.055 –1 –1 5 1L 30.622 30.621 30.981 1 31.088 31.106 –1 2 0 1 30.953 30.949 2 31.460 31.462 1 31.483 31.484 –1 –2 3 2 31.213 31.207 4 31.501 31.509 4 31.594 31.592 –2 1 0 1 31.618 31.616 1L 31.691 31.698 –2 –1 3 2 31.748 31.755 18 31.865 31.883 –1 2 1 8 31.303 31.304 22 31.849 31.854 31.865 Сontinuation of table 1 137 atomic coordinates, isotropic atomic dis- placement parameters, cation occupancies and main selected interatomic distances are presented in Tables 4 and 5. The popu- lations of  four independent positions M = (Zn, Ga) and three incompletely occu- pied Ag sites were refined with keeping the electrical neutrality of the chemical formu- la. The final compositions of the crystals are close to stoichiometric AgZn3Ga(MoO4)5 with a negligible silver deficiency. In the structure AgZn3Ga(MoO4)5 all atoms are located in  general positions. Coordination polyhedra of Mo atoms are tetrahedra with Mo–O distances of 1.714– 1.824  Å, which are similar to  the values found in other molybdates containing a tet- rahedral anion. Cations Zn2+ and Ga3+ are statistically distributed on octahedral posi- tions M1–M4 with the (Zn, Ga)–O bond lengths of 1.940–2.129 Å. Both Ag1 and Ag3 cations are coordinated by four O atoms (Ag1–O 2.358 Å, Ag3–O 2.415 Å), while Ag2 cation has CN = 5 (Ag2–O 2.495 Å). The structure of  AgZn3Ga(MoO4)5 con- sists of MoO4 tetrahedra, couples of edge- shared M(1)O6 octahedra, and trim- ers of  edge-shared M(2)O6, M(3)O6 and Сontinuation of table 1 h k l AgMn3Ga(MoO4)5 AgZn3Ga(MoO4)5 AgCo3Ga(MoO4)5 I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° I / I0 2θobs.,° 2θcal.,° 1 –2 1 2 31.408 31.410 2 31.912 31.899 3 31.945 31.935 2 –1 1 1 31.440 31.428 31.914 1 31.996 31.999 1 –1 5 1 31.853 31.857 3 32.264 32.264 2 32.362 32.364 –1 1 5 1L 31.974 31.980 1 32.590 32.619 0 2 4 2 32.137 32.125 9 32.653 32.689 2 32.654 32.663 2 0 4 4 32.239 32.238 32.647 6 32.741 32.736 2 –1 2 1 32.512 32.535 11 33.027 33.015 1 33.127 33.106 1 2 4 3 32.569 32.567 33.038 7 33.020 33.014 1 –2 2 3 32.655 32.656 5 33.131 33.133 4 33.188 33.186 0 –1 6 2 33.363 33.368 0 –2 4 7 33.135 33.134 16 33.511 33.513 11 33.603 33.601 2 2 0 1 33.214 33.200 33.510 1 33.551 33.568 2 2 1 2 33.311 33.313 6 33.634 33.641 5 33.683 33.681 –2 0 4 1 33.426 33.434 4 33.935 33.941 1 34.059 34.066 1 1 6 1L 33.460 33.454 33.948 –2 –2 1 3 33.847 33.852 11 34.158 34.160 8 34.239 34.239 Cu Kα1 radiation (l = 1.54056 Å) Table 2 Unit-cell parameters for AgA3Ga(MoO4)5 (A = Mn, Zn, Co) A a, Å b, Å c, Å α° β° γ° V, Å3 Mn 6.9844 (3) 7.0519 (4) 17.9700 (8) 87.796 (4) 87.529 (5) 79.386 (4) 868.71 Zn 6.9037 (3) 6.9639 (4) 17.7147 (8) 88.107 (4) 87.440 (4) 78.982 (4) 834.87 Co 6.8810 (4) 6.9657 (4) 17.669 (1) 87.895 (5) 87.344 (5) 78.976 (5) 830.04 138 Table 3 Crystal data and structure refinement for AgZn3Ga(MoO4)5 Structural formula AgZn3Ga (MoO4)5 Formula weight, Mr (g mol −1) 1172.58 Temperature (K) 298(2) Crystal system, space group (#) Triclinic, P1 (2) Unit-cell parameters: a (Å) b (Å) c (Å) α (°) β (°) γ (°) 6.9035 (5) 6.9643 (5) 17.7160 (14) 88.1039 (11) 87.4338 (12) 78.9880 (9) Unit-cell volume, V (Å3) 835.0 (2) Formula unit, Z 2 Calculated density, ρcal (g cm −3) 4.66 Refinement R factors and goodness of fit: wRp Rp Rexp R(F2) χ2 0.0511 0.0382 0.0152 0.05815 3.40 Table 4 Structural parameters for AgZn3Ga(MoO4) 5 Atom Occupancy x y z Uiso Mo1 1 0.2722(8) 0.3095(8) 0.5282(3) 0.030(2) Mo2 1 0.2129(8) 0.8293(9) 0.2856(3) 0.028(2) Mo3 1 0.6843(8) 0.2187(8) 0.3109(3) 0.023(2) Mo4 1 0.2811(9) 0.0522(9) 0.9044(3) 0.029(2) Mo5 1 0.2520(8) 0.5491(8) 0.0863(3) 0.021(2) M1 0.788(1)Zn+0.212(1)Ga 0.1834(12) 0.8241(11) 0.4938(5) 0.0126(3) M2 0.901(1)Zn+0.099(1)Ga 0.1704(14) 0.0855(16) 0.1145(5) 0.045(4) M3 0.798(1)Zn+0.202(1)Ga 0.7829(12) 0.4310(13) 0.1239(4) 0.014(3) M4 0.505(1)Zn+0.495(1)Ga 0.2546(12) 0.3014(13) 0.7370(4) 0.023(3) Ag1 0.323(3)Ag 0.149(3) 0.339(3) 0.2857(12) 0.062(5) Ag2 0.328(3)Ag 0.122(4) 0.308(4) 0.3155(13) 0.062(5) Ag3 0.342(3)Ag 0.097(3) 0.370(3) 0.3445(11) 0.062(5) O1 1 0.511(5) 0.194(5) 0.5163(18) 0.015(1) O2 1 0.289(4) 0.366(4) 0.6238(17) 0.015(1) O3 1 0.171(4) 0.545(5) 0.4601(18) 0.015(1) O4 1 0.130(5) 0.126(5) 0.4978(18) 0.015(1) 139 M(4)O6 octahedra, which are linked by the common vertices to form a 3D framework (Fig. 2). In the large framework cavities, the silver cations are disordered on three close positions with the distances Ag–Ag 0.595(4) Å and 1.101(2) Å. Such a  disordering is also typical of other compounds of this isostructural series [7, 9], suggesting a possible mobility of the Ag+ cations in the compounds. This is favored not only by defects in Ag posi- tions along with their irregular coordina- Сontinuation of table 4 Atom Occupancy x y z Uiso O5 1 0.189(4) 0.872(4) 0.3866(18) 0.015(1) O6 1 0.477(5) 0.719(4) 0.2580(17) 0.015(1) O7 1 0.140(5) 0.053(5) 0.2220(19) 0.015(1) O8 1 0.098(5) 0.641(5) 0.2687(18) 0.015(1) O9 1 0.419(5) 0.280(4) 0.3590(17) 0.015(1) O10 1 0.804(5) 0.191(4) 0.3830(18) 0.015(1) O11 1 0.681(5) 0.995(5) 0.2696(17) 0.015(1) O12 1 0.774(4) 0.370(5) 0.237(2) 0.015(1) O13 1 0.198(4) 0.121(4) 0.997(2) 0.015(1) O14 1 0.468(5) 0.040(4) 0.0841(15) 0.015(1) O15 1 0.831(5) 0.202(5) 0.1174(16) 0.015(1) O16 1 0.238(4) 0.305(5) 0.8544(17) 0.015(1) O17 1 0.249(4) 0.546(4) 0.987(2) 0.015(1) O18 1 0.485(5) 0.488(5) 0.1153(17) 0.015(1) O19 1 0.171(4) 0.778(5) 0.1292(18) 0.015(1) O20 1 0.097(4) 0.410(5) 0.1173(18) 0.015(1) Fig. 1. Observed (black line) and calculated (red line) XRD patterns of AgZn3Ga(MoO4)5. Vertical bars indicate the positions of the Bragg peaks. The lower trace depicts the difference between the experimental and calculated intensity values Fig. 2. Projection views of the structure of AgZn3Ga(MoO4)5 along the a axis. The blue spheres and small red spheres indicate Ag and oxygen atoms, respectively 140 Table 5 Selected interatomic distances(Å) in AgZn3Ga(MoO4) 5 Mo1‑tetrahedron Mo2‑tetrahedron Mo1–O1 –O2 –O3 –O4 1.696(3) 1.764(3) 1.726(3) 1.858(3) 1.761 Mo2–O5 –O6 –O7 –O8 1.819(3) 1.889(3) 1.891(3) 1.698(3) 1.824 Mo3‑tetrahedron Mo4‑tetrahedron Mo3–O9 –O10 –O11 –O12 1.961(3) 1.739(3) 1.747(4) 1.812(3) 1.815 Mo4–O13 –O14 –O15 –O16 1.749(3) 1.726(2) 1.922(3) 1.760(3) 1.789 Mo5‑tetrahedron M1‑octahedron Mo5–O17 –O18 –O19 –O20 1.758(4) 1.683(3) 1.773(3) 1.640(3) 1.714 M1–O1 –O3 –O10 –O4 –O5 –O4 2.092(3) 2.068(3) 2.186(3) 2.070(2) 1.918(3) 2.124(3) 2.076 M2‑octahedron M3‑octahedron M2–O7 –O13 –O19 –O20 –O14 –O15 1.918(3) 2.096(3) 2.144(3) 2.224(3) 2.066(3) 2.325(3) 2.129 M3–O18 –O17 –O15 –O16 –O12 –O20 2.030(3) 1.99(4) 1.572(3) 1.869(3) 2.038(3) 2.143(3) 1.940 M4‑octahedron Ag1‑polyhedron M4–O8 –O11 –O2 –O6 –O16 –O12 2.398(4) 2.033(4) 2.053(3) 1.837(3) 2.079(3) 2.320(3) 2.120 Ag1–O9 –O8 –O7 –O12 2.29(4) 2.080(3) 2.33(4) 2.73(4) 2.358 Ag2‑polyhedron Ag3‑polyhedron Ag2–O9 –O10 –O8 –O7 –O12 2.19(4) 2.70(4) 2.41(4) 2.45(4) 2.725(3) 2.495 Ag3–O9 –O8 –O10 –O3 2.22(4) 2.28(4) 2.62(4) 2.540(3) 2.415 Ag1–Ag2 Ag1–Ag3 0.595(4) 1.101(2) 141 tion, but also a rather flexible polyhedral framework of the NaMg3In(MoO4)5 struc- ture type, which involves interconnected cavities. Electrophysical properties As was noted in the previous section, the structural features of  the obtained molybdates allow us to expect these com- pounds to have the increased ionic con- ductivity. This was already confirmed by us in the case of AgMg3Al(MoO4)5 (σ = = 2.5 × 10−2 S / cm) and AgMn3Al(MoO4)5 (σ = 7.1 × 10−3 S / cm) at 500 °C [7]. In this work as an example, the results of studying electrophysical properties for  AgMn3Ga (MoO4) 5 are presented. It was found that the DC conductivity of ceramic sample AgMn3Ga(MoO4)5, mea- sured with the V7–38 device, is negligible as compared to the ac conductivity (Fig. 3) in temperature region of 100–560 °C. As the platinum electrodes are blocking in the DC conductivity measurement mode, the DC conductivity of AgMn3Ga(MoO4)5 corres- ponds to the electronic one. Therefore, it can be concluded that the AC conductivity is almost equal to the ionic one. It is seen that near room temperature the conductivity is as small as 10–7 S / cm but quickly rises with temperature to va lues of about 10–2 S / cm. It is noteworthy that the conductivity in AgMn3Ga(MoO4)5 increases with temperature in non-monotonic way showing distinct breaks on  lgσ  = f(1 / T) curves at 310 °C. Above these temperature the lgσ = f(1 / T) dependences are almost linear with the small activation ener gy va lue Еа = 0.26 eV. Above 310 °С, the ionic con- ductivity of  AgMn3Ga(MoO4)5 increases up to  2.03∙10–2 S / сm at  500 °С, which is close to the corresponding characte ristics of the known ionic conductors. Conclusions The possibility of  the formation of  silver-containing gallium triple mo- lybdates with Mn, Co, Zn, Ni, analogous to  the phases Ag1–xA1–xR1+x(MoO4)3 and AgA3R(MoO4)5 obtained by  us in  the Ag2MoO4−AMoO4−R2(MoO4)3 (A = Mg, Co; R = Al; A = Mg, R = In) systems, was studied. It was shown that in the Ag2MoO4− AMoO4−Ga2(MoO4)3 (A = Mn, Co, Zn, Ni) systems the NASICON-like phases of the composition Ag1–xA1–xR1+x(MoO4)3 are not formed. The triple molybdates of the composition AgA3Ga(MoO4)5 (A = Mn, Co, Zn) were synthesized and characte- rized. AgNi3Ga(MoO4)5 was not obtained in the single-phase state. It was established that the obtained compounds incongru- ently melt and belong to  the structural type of triclinic NaMg3In(MoO4)5 (sp. gr. P1, Z = 2). The structure of the obtained compounds was refined by  the Rietveld method using the powder diffraction data for AgZn3Ga(MoO4)5. The structural fea- tures of the obtained molybdates allow us to  expect these compounds to  have the increased ionic conductivity. This was Fig. 3. Temperature dependences of the ionic conductivity on heating and cooling for AgMn3Ga(MoO4)5 142 confirmed by  studying electrophysical properties of  AgMn3Ga(MoO4)5. It was shown that the high-temperature electri- cal conductivity of this compound reaches 10–2  S / cm at  Ea = 0.26 eV, which is close to the corresponding characteristics of the known ionic conductors. Acknowledgments The research was carried out within the state assignment of BINM SB RAS, supported in part by the Russian Foundation for Basic Research (Project No. 17-03-00333а) References 1. Kotova IYu. Phase formation in the Ag2MoO4–CoMoO4–Al2(MoO4)3 system. Russ J Inorg Chem. 2014;59:844–8. DOI:10.7868 / S0044457X14080133. 2. Kotova IYu, Korsun VP. Phase in the Ag2MoO4–MgMoO4–Al2(MoO4)3. Russ J Inorg Chem. 2010;55:955–8. DOI: 10.1134 / S0036023610060203. 3. Kotova IYu, Korsun VP. Phase formation in  the system involving silver, mag- nesium, and indium molybdates. Russ J Inorg Chem. 2010;55:1965–9. DOI: 10.1134 / S0036023610120247. 4. Kotova IYu, Belov DA, Stefanovich SYu. Ag1–xMg1–xR1+x(MoO4)3 Ag +-conducting NASICON-like phases, where R = Al or Sc and 0 ≤ x ≤ 0.5. Russ J Inorg Chem. 2011;56:1189−93. DOI: 10.1134 / S0036023611080122. 5. Bouzidi C, Frigui W, Zid MF. Synthèse et structure crystalline d,un maté- riau noir AgMnII3(Mn III 0.26Al0.74)(MoO4)5. Acta Cryst. 2015; E71:299–304. DOI: 10.1107 / S2056989015003345. 6. Nasri R, Chérif SF, Zid MF. Structure cristalline de la triple molybdate Ag0.90Al1.06Co2.94 (MoO4)5. Acta Cryst. 2015; E71:388−91. DOI: 10.1107 / s2056989015005290. 7. Kotova IYu, Solodovnikov SF, Solodovnikova ZA, Belov DA, Stefanovich SYu, Savina AA, Khaikina EG. New series of triple molybdates AgA3R(MoO4)5 (A = Mg, R = Cr, Fe; A = Mn, R = Al, Cr, Fe, Sc, In) with framework structures and mobile silver ion sublattices. J Solid State Chem. 2016;238:121–8. DOI: 10.1016 / j. jssc. 2016.03.003. 8. Balsanova LV. Synthesis of crystals of silver containing oxide phases based on mo- lybdenum, study of their structure and properties. Vestnik VSGUTU. 2015;5:63−9. 9. Kotova IYu, Savina AA, Khaikina EG. Crystal structure of new triple molybdate AgMg3Ga(MoO4)5 from Rietveld refinement. Powder Diffraction. 2017;32(4):255–60. DOI: 10.1017 / S0885715617000811. 10. Yanushkevich TM, Zhukovsky VM, Ustyantsev VM. Fazovaya diagramma sis- temy NiO‒МоО3. [Phase diagram of the system NiO‒МоО3]. Russ J Inorg Chem. 1974;19(7):1932–6. 11. Zhukovsky VM, Tkachenko EV. Fazovye ravnovesiya v molibdatnykh sistemakh. [Phase equilibria in molybdate systems]. Zbornik nauchnykh trudov. “Fizicheskaya khimiya okislov”. Moscow: Nauka; 1981.106–15. Russian. 12. Reichelt W, Weber T, Soehnel T. at al. Electronic structure and luminescence mecha- nisms in ZnMoO4 crystals. J Phys: Condes Mater. 2011;23:244‒59. 13. Tsyrenova GD, Bazarova JG, Mokhosoev MV. Phase equilibria in systems МеО– МоО3 (Me–Mg, Мп, Zn). Russ J Inorg Chem. 1986;31(12):3120–3. 143 14. Rajaram P, Viswanathan B, Aravamudan G. Studies on the formation of manganese molybdates. Thermochim acta. 1973;7 (2):123–9. 15. Kohlmuller R, Faurie J.-P. Etude des systemes MoO3–Ag2MoO4 et MoO3–MO (M–Cu, Zn, Cd). Bull Soc chim. France. 1968;11:4379–82. 16. Larson AC, Von Dreele RB. General Structure Analysis System (GSAS) (Report LAUR 86–748). 2004. Los Alamos, New Mexico: Los Alamos National Laboratory. 17. Shannon RD. Revised effective ionic radii and systematic studies of  interatom- ic distances in  dalides and chalcogenides. Acta Cryst. 1976; A32:751–67. DOI: 10.1107 / S0567739476001551. 18. Gates Stacy D, Julie A, Lind C. Gates Non-hydrolytic sol-gel synthesis, properties, and high-pressure behavior of gallium molybdate. J Mater Chem. 2006;16:4214–9. DOI:10.1039 / B608864C. 19. Perepelitsa AP, Golub AM, Badayev YuB, Shapoval VN. Double molybdates of alu- minum, gallium, indium, chromium, iron and bismuth with monovalent silver and thallium. Russ J Inorg Chem. 1977;22(4):994–7. 20. Klevtsova RF, Vasiliev AD, Kozhevnikova NM, Glinskaya LA, Kruglik AI, Kotova  IYu. Synthesis and crystal structural study of  ternary molybdate NaMg3In(MoO4)5. J Struct Chem. 1994;34:784−8. 21. Rietveld HM. A profile refinement method for nuclear and magnetic structures. J Appl Cryst. 1969;2:65–71.