Monoclinic Cell Research Articles

Structural interplay between strontium and calcium in α-CaHPO4 and β-SrHPO4

The ability of strontium ion to inhibit the abnormally high bone resorption, which occurs in pathologies characterized by loss of bone substance, has stimulated a number of research on strontium substituted/doped calcium phosphates. However, no information was available up to now on strontium substitution to calcium in the structure of α-CaHPO4, monetite, in spite of the involvement of this phosphate in the composition of biomaterials for hard tissue substitution/repair and although it is isomorphous with α-SrHPO4. Herein, we investigated the substitution of strontium to calcium in the structure of α-CaHPO4, as well as the replacement of calcium for strontium in the structure of a further polymorph of SrHPO4, namely β-SrHPO4. To this purpose, monetite at increasing degree of strontium substitution for calcium was synthesized by means of direct synthesis in aqueous solution, as well as through thermal treatment of strontium-substituted brushite; whereas the synthesis of β-SrHPO4 was carried out at low temperature. The results of structural refinements, spectroscopic analysis and electron microscopy investigation indicate that the method of synthesis has a great influence on the range of strontium incorporation into α-CaHPO4, which can reach 100 at%. The morphology of the synthesized materials is also remarkably dependent on composition. The analysis of the products synthesized at low temperature shows that the upper limit of possible substitution of calcium to strontium in the structure of β-SrHPO4 is much more limited, just up to about 20 at%. Moreover, powder X-ray analysis of β-SrHPO4 states that it crystallizes with a monoclinic cell in the space group P21/c.

Synthesis, crystal structure, and lithium ion conductivity of Li2.10Sn0.90O2.85

A white bulk sample of Li2.10Sn0.90O2.85 was prepared by heating a compact pellet of a Li2O and SnO2 powder mixture with a molar ratio of 1.10:0.95 at 1000 °C for 6 h in Ar and consisted of colorless transparent crystal grains with sizes in the range of 20–80 μm. X-ray diffraction (XRD) reflections from a single crystal taken from the grains were indexed with C-centered monoclinic cell parameters (a = 5.29120(10) Å, b = 9.2033(2) Å, c = 10.0676(2) Å, β = 100.5030(10)°). The crystal structure was determined with the space group C2/c (No. 15) using Li2SnO3 as a starting model. The final structure refinement was performed by partial substitution of Li+ for Sn4+ and the introduction of O2− defects with a formula of Li2(Li0.10Sn0.90)O2.85. Interstitial sites and continuous disordered distribution of Li+ ions were depicted in a differential Fourier synthesis map and an electron density distribution (EDD) map by the maximum entropy method (MEM). The disordered Li+ distribution was also revealed as broad peaks by 6Li magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The Li+ conductivity of Li2.10Sn0.90O2.85 measured at 25 °C was 1.0 × 10−6 S·cm−1, which was 105 times greater than that of Li2SnO3.

Molecular dynamics simulation of extension-induced crystallization of branched bimodal HDPE: Unraveling the effects of short-chain branches.

Bimodal HDPE models were designed for extension-induced crystallization imitating the architecture of industrial bimodal HDPE copolymerized with ethylene and 1-butene, 1-hexene, or 1-octene. Crystallites of bimodal HDPE experienced the emergence of precursors, shish nuclei, and lamellae. The compact conformation of branched polymers impeded the rolling-over, deposition, and folding of chains on the substrate, and thus the formation of nuclei and lamella. Moreover, this retardation was intensified with the rising branch density and length, causing a depression of crystallinity and an increment of tie-chains concentration. Besides, when branches were all located on long chains, the compact conformation enlarged the resistance to the disentanglement of main chains, thus relatively fewer branched long chains were involved in the precursors or nuclei, resulting in the attenuation of lamella formation. Furthermore, for ethyl branched polymers, the coexistent orthorhombic and monoclinic crystallites were built up, and a few expanded monoclinic cells occurred for butyl branches because of the larger butyl reeling into lamella, while hexagonal crystals were created for ethyl/1-hexyl copolymers because of cocrystallization. Additionally, relative to ethyl, larger butyl and hexyl were preferential to be repelled outside crystals to form tie-chains, and hexyl branched polymers acquired relatively fewer tie-chains because of hexagonal eutectoid.

Efficient synthesis of diversely substituted pyrazolo[1,5-a]pyrimidine derivatives promoted by ultrasound irradiation in water and their antibacterial activities

A green synthetic route leading to the discovery of a series of diversely substituted pyrazolo[1,5-a]pyrimidines, having CO2Et group embedded at position-2 has been unraveled in this article. A series of formylated active proton compounds that were chosen to react with a carboxylate substituted-3-aminopyrazole under ultrasonic irradiation in the presence of a mild acid as a catalyst and aqueous ethanol medium afforded the desired products. The molecular structures of all these synthesized compounds were established by their spectral and analytical data. A model molecule 3d, subjected to single-crystal X-ray crystallography analysis further confirms their molecular structure. The crystal crystallized to a monoclinic cell with P21/c space group, a = 7.468 (5) Å, b = 27.908 (17) Å, c = 7.232 (4) Å, β = 104.291 (7)o, V =1460.7(15) Å3, Z = 4, μ(MoKα) = 0.096 mm-1, Dcalc = 1.352 Mg/m3 16667 measured reflection (5.63 ≤ 2Θ ≤ 57.57°), 3720 unique (Rint = 0.0965, Rsigma = 0.0945) which were used in all calculations. The final R1 was 0.0750 (I > 2σ(I)) and wR2 was 0.2226 (all data). These compounds were further explored for their antibacterial potential, and a few of them have exhibited encouraging results.

Crystal Structure and Hirshfeld Surface Analysis of (E)-1-(4-Bromophenyl)-2-(2,2-Dichloro-1-(4-Fluorophenyl)vinyl)diazene

The CuCl-catalyzed olefination with CCl4 in the presence of tetramethylethylenediamine in DMSO leads to the formation of (E)-1-(4-bromo-(2,2-dichloro-1-(4-fluorophenyl)vinyl)-diazene from (E)-1-(4-bromophenyl)-2-(4-fluorobenzylidene)hydrazine. The structure was confirmed by conventional spectroscopy techniques (nuclear magnetic resonance, electrospray ionization mass spectrometry) and determined by X-ray diffraction analysis of single crystals. The title compound crystallized in a monoclinic cell (space group P21/c, Z = 4) with a centrosymmetric arrangement of molecules in the crystal structure, showing interesting non-covalent interactions that were studied by Hirshfeld surface analysis.

Structure, Infrared and Raman spectroscopic studies of new AII(SbV0.50CrIII0.50)(PO4)2 (A = Ba, Sr, Pb) yavapaiite phases

<p class="Mabstract">Three new A<sup>II</sup>(Sb<sub>0.5</sub>Cr<sub>0.5</sub>)(PO<sub>4</sub>)<sub>2</sub> (A<sup>II</sup> = Ba, Sr, Pb) yavapaiite phases, abbreviated as [ASbCr], have been successfully synthesized by a conventional solid-state reaction in air atmosphere. Their crystal structures have been investigated by Rietveld analysis from the X-ray powder diffraction method. Results show that Ba(Sb<sub>0.5</sub>Cr<sub>0.5</sub>)(PO<sub>4</sub>)<sub>2</sub> crystallizes in monoclinic <em>C</em>2<em>/m</em> space group (Z = 2) with cell parameters a = 8.140(1) Å; b = 5.175(1) Å; c = 7.802(1) Å and β = 94.387(1)°. Structures of A<sup>II</sup>(Sb<sub>0.5</sub>Cr<sub>0.5</sub>)(PO<sub>4</sub>)<sub>2</sub> (A<sup>II </sup>= Sr, Pb) compounds are comparable, and both crystallize in a distorted yavapaiite structure with <em>C</em>2<em>/c</em> space group (Z = 4). Obtained monoclinic cell parameters are: a = 16.5038(2) Å; b = 5.1632(1) Å; c = 8.0410(1) Å; β = 115.85(1) for [SrSbCr] and a = 16.684(2) Å; b = 5.156(1) Å c = 8.115(1) Å; β = 115.35(1)° for [PbSbCr]. Infrared and Raman spectroscopic study was undertaken to provide information about vibrations bonds within the studied yavapaiite materials.</p>

Spectroscopic, optical, magnetic and dielectric investigation of the orthoborate Ba2Co(BO3)2 nanopowder

Nano-polycrystalline phase of Ba2Co(BO3)2, has been successfully obtained by the standard solid-state reaction. The Ba2Co(BO3)2 crystallizes in the monoclinic cell with the space group C2/m. The cell parameters are: a = 12.027 A, b = 5.340 A, c = 10.295 A, and β = 117.228°. The average grain size determined from Debye–Scherer’s equation is 40.29 nm. The surface morphology of the studied borate is consisting of the regular-shaped particles and the SEM reveals homogenous particles of nanotubes shapes. The elemental composition is confirmed by Energy Dispersive Spectrometry (EDS). The infrared and Raman studies confirm the existence of the BO3 groups. The calculated gap energy (E = 3.57 eV for the indirect mode and E = 3.9 eV for the direct one) is reported which is typical for wide-band-gap semiconductor materials. The magnetic measurements established that the predominant interactions in this borate are antiferromagnetic. The thermal investigation of the borate studied by the differential scanning calorimetry (DSC) highlights several anomalies, which could correspond either to phase transitions or to change in the physical behavior of the material. These phenomena are observed and interpreted by means of the dielectric study at high temperature.

Crystal structure and luminescence properties of thermally stable Sm3+-doped Sr9In(PO4)7 orange-red phosphor

A series of novel phosphate orange-red phosphor, Sr9In(PO4)7:xSm3+ (0.01 < x < 0.30), were successfully synthesized from high-temperature solid-state synthesis in this work. Their crystal structure has been analyzed by the Rietveld refinement, which shows Sr9In(PO4)7 consists of a monoclinic cell (C2/c), which also confirms the successful doping, preferential site occupancy and local ligand environment of Sm3+. Luminescence properties of the samples have been systematically investigated including excitation and emission spectra, quantum efficiency, concentration quenching, fluorescence decay and temperature-dependent luminescence properties. Photoluminescence spectra exhibited typical peaks, corresponding to 4G5/2 → 6HJ transitions of Sm3+ ions, where J = 5/2, 7/2, 9/2, and 11/2, respectively. Moreover, the concentration quenching result revealed that the optimal doping content of Sm3+ was 0.15 mol, and based on the Dexter theory, the energy transfer between Sm3+ ions was found in dipole-dipole interactions. The quantum yield of Sr9In(PO4)7:0.15Sm3+ phosphor was acceptable (58.5%). Most importantly, the emission intensity of Sr9In(PO4)7:0.15Sm3+ remains constant (>97%) below 150 °C and the configurational coordinate diagram analysis demonstrated excellent thermal stability of the Sr9In(PO4)7:Sm3+ phosphor, which is superior to that of the previously reported and commercially available phosphors. These results suggest that the Sr9In(PO4)7:Sm3+ phosphor is a promising orange-red phosphor materials for white light emitting diodes.

Preparation and Characterization of Paramagnetic Bis (8-Hydroxyquinoline) Manganese Crystals.

The magnetic properties of π-conjugated bis (8-hydroxyquinoline) manganese (Mnq2) crystals are investigated. Rod-shaped Mnq2 crystals are prepared by using the physical vapor deposition method. Field emission scanning electronic microscopy spectra show that the Mnq2 nanorods have perfect plane quadrangular ends. Energy dispersive spectrometer and X-ray photoelectron spectroscopy analysis demonstrates that the powders and nanorods are the same compound with a high purity. X-ray diffraction analysis shows the high crystal quality of the prepared Mnq2 nanorods. The magnetic measurement, using alternating gradient magnetometer and magnetic property measurement system superconducting quantum interference device vibrating sample magnetometer, indicates that the prepared Mnq2 nanorods show a paramagnetic property at room temperature. First-principles density functional theory (DFT) calculations are used to study the electronic structure and magnetic properties of the prepared Mnq2 crystals. DFT calculations show that the magnetic moment of the Mnq2 isolated molecule is 5 μB, which mainly comes from the localized Mn 3d orbital. The energy difference between the antiferromagnetic and ferromagnetic states of the Mnq2 monoclinic cell is only 0.1 meV, which may explain the paramagnetic property observed in the prepared Mnq2 nanorods and also indicates the difficulty of preparing intrinsic ferromagnetic Mnq2 crystals.

Crystallization of metastable monoclinic carnallite, KCl·MgCl2·6H2O: missing structural link in the carnallite family.

During evaporation of natural and synthetic K-Mg-Cl brines, the formation of almost square plate-like crystals of potassium carnallite (potassium chloride magnesium dichloride hexahydrate) was observed. A single-crystal structure analysis revealed a monoclinic cell [a = 9.251 (2), b = 9.516 (2), c = 13.217 (4) Å, β = 90.06 (2)° and space group C2/c]. The structure is isomorphous with other carnallite-type compounds, such as NH4Cl·MgCl2·6H2O. Until now, natural and synthetic carnallite, KCl·MgCl2·6H2O, was only known in its orthorhombic form [a = 16.0780 (3), b = 22.3850 (5), c = 9.5422 (2) Å and space group Pnna].

Structural and vibrational behavior of cubic Cu1.80(3)Se cuprous selenide, berzelianite, under compression

We have performed an experimental study of the crystal structure and lattice dynamics of cubic Cu1.80(3)Se at ambient temperature and high pressures. Two reversible phase transitions were found at 2.9 and 8.7 GPa. The indexation of the angle-dispersive synchrotron x-ray diffraction patterns suggests a large orthorhombic cell and a monoclinic cell for the high-pressure phases. Raman measurements provide additional information on the local structure. The compressibility of the three ambient temperature phases has been determined and compared to that of other sulphides and selenides.

Layer stacking disorder in Mg-Fe chlorites based on powder X-ray diffraction data

AbstractThe primary aim of this study was the accurate determination of unit-cell parameters and description of disorder in chlorites with semi-random stacking using common X-ray diffraction (XRD) data for bulk powder samples. In the case of ordered chlorite structures, comprehensive crystallographic information can be obtained based on powder XRD data. Problems arise for samples with semi-random stacking, where due to strong broadening of hkl peaks with k ≠ 3n, the determination of unit-cell parameters is demanding. In this study a complete set of information about the stacking sequences in chlorite structures was determined based on XRD pattern simulation, which included determining a fraction of layers shifted by ±1/3b, interstratification with different polytypes and 2:1 layer rotations.A carefully selected series of pure Mg-Fe tri-trioctahedral chlorites with iron content in the range from 0.1 to 3.9 atoms per half formula unit cell was used in the study. In addition, powder XRD patterns were carefully investigated for the broadening of the odd-number basal reflections to determine interstratification of 14 and 7 Å layers. These type of interstratifications were finally not found in any of the samples. This result was also confirmed by the XRD pattern simulations, assuming interstratification with R0 ordering.Based on h0l XRD reflections, all the studied chlorites were found to be the IIbb polytype with a monoclinic-shaped unit cell (β ≈ 97°). For three samples, the hkl reflections with k ≠ 3n were partially resolvable; therefore, a conventional indexing procedure was applied. Two of the chlorites were found to have a monoclinic cell (with α, γ = 90°). Nevertheless, among all the samples, the more general triclinic (pseudomonoclinic) crystal system with symmetry C1 was assumed, to calculate unit-cell parameters using Le Bail fitting.A detailed study of semi-random stacking sequences shows that simple consideration of the proportion of IIb-2 and IIb-4/6 polytypes, assuming equal content of IIb-4 and IIb-6, is not sufficient to fully model the stacking structure in chlorites. Several, more general, possible models were therefore considered. In the first approach, a parameter describing a shift into one of the ±1/3b directions (thus, the proportion of IIb-4 and IIb-6 polytypes) was refined. In the second approach, for samples with slightly distinguishable hkl reflections with k ≠ 3n, some kind of segregation of individual polytypes (IIb-2/4/6) was considered. In the third approach, a model with rotations of 2:1 layers about 0°, 120°, 240° was shown to have the lowest number of parameters to be optimized and therefore give the most reliable fits. In all of the studied samples, interstratification of different polytypes was revealed with the fraction of polytypes being different than IIbb ranging from 5 to 19%, as confirmed by fitting of h0l XRD reflections.

On the synthesis and structure of the copper-molybdenum oxide bronzes: Monoclinic Cu2Mo10O30 and orthorhombic CuMo9O26

Cu2Mo10O30 was prepared as a monophasic material comprising dark blue platy crystals by reacting Cu with MoO3 under argon at 550 ​°C. Single-crystal X-ray diffractometry showed that Cu2Mo10O30 is a stoichiometric compound that crystallizes with a monoclinic (C2/c) cell: a ​= ​16.6359(6); b ​= ​9.3112(3); c ​= ​27.1597(9) Å; β ​= ​102.621(3)° (Z ​= ​8). Electron paramagnetic resonance spectroscopy revealed that Cu2Mo10O30 displays mixed-valency; (CuI2−xCuIIx)(MoV2+xMoVI8−x)O30 (0 ​≪ ​x ​≤ ​2). Differential scanning calorimetry and in situ high-temperature powder X-ray diffractometry showed that Cu2Mo10O30 decomposes ≳550 ​°C under an inert atmosphere. Dark blue acicular crystals of CuMo9O26 were discovered as a side-product in materials prepared inside evacuated glass ampoules at 500 ​°C. Single-crystal X-ray diffractometry showed these to crystallize with an orthorhombic (Pmmn) cell: a ​= ​3.74190(10); b ​= ​26.4941(4); c ​= ​9.15300(10) Å; (Z ​= ​2). Rietveld refinement of the powder X-ray diffraction data for these materials revealed Cu2Mo10O30 with minor CuMo9O26 and ‘Cu0.1MoO3’.

OPTIMIZATION OF MONOCLINIC Cu2SnS3 (CTS) THIN FILM SOLAR CELL PERFORMANCES THROUGH NUMERICAL ANALYSIS

Investigation on the performance of monoclinic phase copper tin sulfide (CTS) based thin film solar cells has been carried out numerically by AMPS-1D simulation software. Based on proposed cell structure, the influence of carrier concentration and thickness of both absorber and buffer layers as well as the work function of back contact metal are studied to enhance the output performance of monoclinic phase CTS thin film solar cell. The effect of operating temperature is also tested for CTS solar cell to ensure the sustainability at outdoor installation. After optimizing the thickness and carrier concentration of both layers, the best CTS cell is delivers 9.61% efficiency with back contact of molybdenum. However, after optimization of back contact metal work function the conversion efficiency is further increased to 17.87% for tungsten as back contact metal with a work function of 5.25 eV. The increased temperature shows a negative effect on output performance with a decline efficiency rate of -0.33/K. All these simulation results will give some important guides for feasibly fabricating higher efficiency CTS solar cells.

Structural study of the pressure-induced metal-insulator transition in LiV2O4

At ambient pressure the spinel $\mathrm{Li}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ is a metal with a heavy fermion ground state. However, under applied pressure a transition to an insulating, nonmagnetic state occurs. Powder x-ray diffraction has been used to study structural changes associated with this transition, and reveals that the ambient-pressure $Fd\overline{3}m$ spinel structure distorts to a monoclinic cell of $C2/m,C2$, or $Cm$ symmetry above 11 GPa at low temperatures. The changes of structure and properties provide evidence for orbital molecule formation in the cubic phase at high pressures and low temperatures that leads to long-range orbital molecule order in the monoclinic phase.

Elucidation of site symmetry, location, bond, ground state of Cu2+ ions in lithium sulphate monohydrate single crystal through EPR and optical studies

The highly efficient non linear optical (NLO) lithium suphate monohydrate (LSMH) single crystal with well-developed faces is obtained in a few days by slow evaporation of aqueous solutions at room temperature. Small amount of copper II sulphate pentahydrate is added as the paramagnetic impurity into the system. The powder XRD study shows the monoclinic cell dimension of Cu2+ doped LSMH single crystal. Also FTIR analysis reveals the existence of host in a crystal. The single crystal EPR investigation talks about the presence of copper ion. Even though more than one site is noticed, two are followed and reported. The principle values g and A parameters were calculated for both the sites. The spin Hamiltonian parameters found for both the sites, indicate the rhombic local crystal field symmetry around the impurity ion Cu2+, which is further confirmed by optical absorption studies. Interestingly, both the paramagnetic ions enter the lattice interstitially. The type of bonding between the metal ligand bands for site I and site II are found to be moderate ionic and covalent nature. The ground state wave function of both the sites are observed as dx2−y2, which is also supported by Rache parameter and optical studies.

Crystal structure, spectroscopic, optical, thermal and magnetic studies of new orthoborate Sr2Co(BO3)2

Single crystals of a novel distrontium cobalt diborate, Sr2Co(BO3)2, were successfully obtained from the melt at 1200 ​°C of the polycrystalline material. The powder of Sr2Co(BO3)2 compound was synthesized using standard solid state reaction at 850 ​°C. The refinement of the structure shows that Sr2Co(BO3)2 crystallizes in the monoclinic cell with the space group C2/m. The crystal structure is built from [CoO6] octahedra linked to [BO3] triangles by the vertices and to the SrO9 polyhedra by sharing two faces. The infrared analysis confirms the existence of BO3 vibrations group’s. The calculated gap energy is Egap ​= ​3.5eV for indirect gap model and Egap ​= ​3.75eV for direct gap one. The magnetic measurements show that antiferromagnetic interactions are predominant in the studied borate. The high temperature X-ray diffraction and the differential scanning calorimetry allow to observe two anomalies in the temperature range of 400–800 ​°C which correspond to the phase transitions of Sr2Co(BO3)2.

Synthesis, characterization and luminescence properties of manganese phosphate Mn3(PO4)2

Abstract A great deal of research has concerned the study of the photoluminescent properties of new materials. These studies are motivated by many potential applications in a wide variety of fields such as optical telecommunications, lasers, lighting, radiation detection and photovoltaic. In the present work, we investigate the structural, microstructural, vibrational and luminescence properties of the system Mn3(PO4)2 as a new luminescent material. Polycrystalline sample was elaborated using a coprecipitation technique. The sample was then characterized using X-ray diffraction, scanning electron microscopy, Infrared spectroscopy and luminescence analyses. X-ray diffraction profile analyses showed that the monoclinic crystal cell, was observed. The scanning electron microscopy experiments showed a homogeneous distribution of morphologies and crystallite sizes. The functional groups were indicated by Fourier transform infrared spectroscopy. The Luminescence experiments were performed under UV–visible light irradiation (364 and 633 nm). The integrated intensity of luminescence showed a maximum value in the presence of the powder Mn3(PO4)2.

The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2 AMnTe3 (A=K, Rb), and NaCsMnTe2

Abstract A series of new sodium and mixed Na/A (A = K, Rb, Cs) tellurido manganates have been synthesized from melts of the pure elements (or MnTe) at maximum temperatures of 600–1000°C. The monoclinic crystal structures of the two pure sodium salts Na2Mn2Te3 (space group C2/c, a = 1653.68(2), b = 1482.57(2), c = 773.620(10) pm, β = 117.52°, Z = 8, R1 = 0.0225) and Na2Mn3Te4 (space group C2/m, a = 1701.99(3), b = 438.741(8), c = 691.226(12) pm, β = 90.3171(8)°, Z = 2, R1 = 0.0270) are both based on a hexagonal close packed Te2− arrangement. Na2Mn2Te3 is isotypic with Na2Mn2S3 and Na2Mn2Se3 and contains layers of [MnTe4] tetrahedra, which are connected via common edges to form tetramers [Mn4Te6]. These tetramers are further connected via μ 3-Te atoms. Na2Mn3Te4 crystallizes in a new structure type, recently also reported for the selenido salt Na2Mn3Se4. Mn(2) forms ribbons of vertex-sharing dinuclear units ∞ 1 [ Te 2 / 2 MnTe 2 MnTe 2 / 2 ] $_\infty ^1[{\rm{T}}{{\rm{e}}_{2/2}}{\rm{MnT}}{{\rm{e}}_2}{\rm{MnT}}{{\rm{e}}_{2/2}}]$ running along the short b axis of the monoclinic cell. The Te atoms of these ribbons are also the ligands of edge-sharing [Mn(1)Te6] chains of octahedra. Similar to Na2Mn2Te3, the Na+ cations are octahedrally coordinated and the cations occupy tetrahedral (Mn2+) and octahedral (Na+, Mn2+) voids in the close Te2− packing. The isotypic K/Rb salts Na2 AMnTe3 crystallize in a new structure type (orthorhombic, space group Pmc21, a = 1069.70(4)/1064.34(2), b = 1350.24(5)/1350.47(3), c = 1238.82(4)/1236.94(3) pm, Z = 4, R1 = 0.0445/0.0210). In contrast to the simple formula indicating a Mn(III) compound, the complex structure contains one layer consisting of undulated chains of edge-sharing tetrahedra ∞ 1 [ Mn II Te 4 / 2 ] $_\infty ^1[{\rm{M}}{{\rm{n}}^{{\rm{II}}}}{\rm{T}}{{\rm{e}}_{4/2}}]$ separated by free ditelluride dumbbells [Te2]2− and a second layer containing a complex chain of edge- and vertex-sharing [MnIITe4] tetrahedra, in which Mn(II) is coordinated to μ 1- and μ 2-Te2− ligands and an η 1-ditellurido ligand. The cesium salt NaCsMnTe2 (orthorhombic, space group Cccm, a = 694.21(2), b = 1536.57(4), c = 664.47(2) pm, Z = 4, R1 = 0.0131) likewise forms a new structure type, which is an ordered superstructure of ThCr2Si2. Linear chains ∞ 1 [ MnTe 4 / 2 ] $_\infty ^1[{\rm{MnT}}{{\rm{e}}_{4/2}}]$ of edge-sharing tetrahedra are connected with similar chains ∞ 1 [ NaTe 4 / 2 ] $_\infty ^1[{\rm{NaT}}{{\rm{e}}_{4/2}}]$ to form [NaMnTe2] layers. The larger alkali cations Cs+ between the layers exhibit a cubic (CN = 8) coordination.

Phase equilibria in the quasi-binary system Zn7Sb2O12–Li3Zn3Sb3O12 and thermal properties of Li3xZn7-4xSb2+xO12 solid solutions

An extensive range of spinel-like solid solutions was found in the system Zn7Sb2O12–Li3Zn3Sb3O12 with general formula Li3xZn7-4xSb2+xO12: 0.25 ≤ x ≤ 0.65. These solid solutions are isostructural with the spinel α-Zn7Sb2O12. The Li3Zn3Sb3O12 (LiZnSbO4) end-member shows two polymorphic forms: high-temperature α-Li3Zn3Sb3O12 with an orthorhombic cell and low-temperature β-Li3Zn3Sb3O12 with a monoclinic cell. These polymorphs show a reversible transformation at 1275 ± 25 °C. The α-Li3Zn3Sb3O12 was also prepared as a metastable phase by direct synthesis at low temperatures, 900 °C. The sub-solidus phase diagram of Li2O–ZnO–Sb2O5 has been determined. Additionally, the thermal and optical properties of Li3xZn7-4xSb2+xO12 (0.35 ≤ x ≤ 0.65) solid solutions were measured. The thermal properties of sintered samples iso-structural to α-Zn7Sb2O12 displayed a heat dissipation related to Li+ and Sb5+ content having a maximum at x = 0.55. The optical band-gap showed a linear shift toward higher energies as the Li+ and Sb5+ content increased.