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1.
The ternary rare-earth zinc antimonides REZn1-xSb2 (RE=La, Ce, Pr, Nd, Sm, Gd, Tb) were prepared by heating at 1050 °C followed by annealing at 600 °C. For all members, single-crystal X-ray diffraction studies indicated that the Zn deficiency is essentially fixed, corresponding to the formula REZn0.6Sb2, with no appreciable homogeneity range. These compounds adopt the HfCuSi2-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). Single-crystal electrical resistivity measurements confirmed the occurrence of an abrupt resistivity decrease near 4 K for RE=Ce, and a less pronounced one for RE=La, Pr, and Gd. Except for the ferromagnetic Ce (Tc=2.5 K) and antiferromagnetic Tb (TN=10 K) members, all remaining compounds exhibit no long-range magnetic ordering down to 2 K, instead showing temperature-independent (RE=La), van Vleck (RE=Sm), or Curie-Weiss paramagnetism (RE=Pr, Nd, Gd). 相似文献
2.
Stanislav S. Stoyko 《Journal of solid state chemistry》2011,184(9):2360-11161
The ternary rare-earth zinc arsenides REZn1−xAs2 (RE=La-Nd, Sm) were prepared by reaction of the elements at 800 °C. Single-crystal and powder X-ray diffraction analysis revealed a defect SrZnBi2-type average structure for the La member (Pearson symbol tI16, space group I4/mmm, Z=4; a=4.0770(9) Å, c=20.533(5) Å), in contrast to defect HfCuSi2-type average structures for the remaining RE members (Pearson symbol tP8, space group P4/nmm, Z=2; a=4.0298(5)-3.9520(4) Å, c=10.222(1)-10.099(1) Å in the progression from Ce to Sm). The homogeneity range is not appreciable (estimated to be narrower than 0.6<1−x<0.7 in SmZn1−xAs2) and the formula REZn0.67As2 likely represents the Zn-rich phase boundary. The Ce-Nd members are Curie-Weiss paramagnets. LaZn0.67As2 shows activated behavior in its electrical resistivity, whereas SmZn0.67As2 exhibits anomalies in its temperature dependence of the electrical resistivity. 相似文献
3.
Haiying Bie 《Journal of solid state chemistry》2009,182(1):122-13843
The ternary rare-earth chromium germanides RECrxGe2 (RE=Sm, Gd-Er) have been obtained by reactions of the elements, either in the presence of tin or indium flux, or through arc-melting followed by annealing at 800 °C. The homogeneity range is limited to 0.25?x?0.50 for DyCrxGe2. Single-crystal and powder X-ray diffraction studies on the RECr0.3Ge2 members revealed that they adopt the CeNiSi2-type structure (space group Cmcm, Z=4, a=4.1939(5)-4.016(2) Å, b=16.291(2)-15.6579(6) Å, c=4.0598(5)-3.9876(2) Å in the progression for RE=Sm to Er), which can be considered to be built up by stuffing transition-metal atoms into the square pyramidal sites of a “REGe2” host with the ZrSi2-type structure. (The existence of YbCr0.3Ge2 is also implicated.) Only the average structure was determined here, because unusually short Cr-Ge distances imply the development of a superstructure involving distortions of the square Ge net. Magnetic measurements on RECr0.3Ge2 (RE=Gd-Er) indicated that antiferromagnetic ordering sets in below TN (ranging from 3 to 17 K), with additional transitions observed at lower temperatures for the Tb and Dy members. 相似文献
4.
Marija Borna Alim Ormeci Ulrich Burkhardt Raul Cardoso-Gil 《Journal of solid state chemistry》2011,184(2):296-303
Application of high-pressure high-temperature conditions (3.5 GPa at 1673 K for 5 h) to mixtures of the elements (RE:B:S=1:3:6) yielded crystalline samples of the isotypic rare earth-thioborate-sulfides RE9[BS3]2[BS4]3S3, (RE=Dy-Lu), which crystallize in space group P63 (Z=2/3) and adopt the Ce6Al3.33S14 structure type. The crystal structures were refined from X-ray powder diffraction data by applying the Rietveld method. Dy: a=9.4044(2) Å, c=5.8855(3) Å; Ho: a=9.3703(1) Å, c=5.8826(1) Å; Er: a=9.3279(12) Å, c=5.8793(8) Å; Tm: a=9.2869(3) Å, c=5.8781(3) Å; Yb: a=9.2514(5) Å, c=5.8805(6) Å; Lu: a=9.2162(3) Å, c=5.8911(3) Å. The crystal structure is characterized by the presence of two isolated complex ions [BS3]3- and [BS4]5- as well as [□(S2-)3] units. 相似文献
5.
Volodymyr Babizhetskyy Hansjürgen Mattausch Régis Gautier Jean-François Halet 《Journal of solid state chemistry》2011,184(7):1671-1681
New ternary rare-earth metal boride carbides RE25B14C26 (RE=Pr, Nd) and Nd25B12C28 were synthesized by co-melting the elements. Nd25B12C28 is stable up to 1440 K. RE25B14C26 (RE=Pr, Nd) exist above 1270 K. The crystal structures were investigated by means of single-crystal X-ray diffraction. Nd25B12C28: space group P, a=8.3209(7) Å, b=8.3231(6) Å, c=29.888(2) Å, α=83.730(9)°, β=83.294(9)°, γ=89.764(9)°. Pr25B14C26: space group P21/c, a=8.4243(5) Å, b=8.4095(6) Å, c=30.828(1) Å, β=105.879(4)°, V=2100.6(2) Å3, (R1=0.048 (wR2=0.088) from 2961 reflections with Io>2σ(Io)); for Nd25B14C26 space group P21/c, Z=2, a=8.3404(6) Å, b=8.3096(6) Å, c=30.599(2) Å, β=106.065(1)°. Their structures consist of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with cumulene-like molecules [B2C4]6− and [B3C3]7−, nearly linear [BC2]5− and bent [BC2]7− units and isolated carbon atoms. Structural and theoretical analysis suggests the ionic formulation for RE25B14C26: (RE3+)25[B2C4]6−([B3C3]7−)2([BC2]5−)4([BC2]7−)2(C4−)4·5e− and for Nd25B12C28: (Nd3+)25([B2C4]6−)3([BC2]5−)4([BC2]7−)2(C4−)4·7e−. Accordingly, extended Hückel tight-binding calculations indicate that the compounds are metallic in character. 相似文献
6.
Four new isostructural rare earth manganese stannides, namely RE3MnSn5−x (x=0.16(6), 0.29(1) for RE=Tm, x=0.05(8), 0.21(3) for RE=Lu), have been obtained by reacting the mixture of corresponding pure elements at high temperature. Single-crystal X-ray diffraction studies revealed that they crystallized in the orthorhombic space group Pnma (No. 62) with cell parameters of a=18.384(9)-18.495(6) Å, b=6.003(3)-6.062(2) Å, c=14.898(8)-14.976(4) Å, V=1644.3(14)-1679.0(9) Å3 and Z=8. Their structures belong to the Hf3Cr2Si4 type and feature a 3D framework composed of 1D [Mn2Sn7] chains interconnected by [Sn3] double chains via Sn-Sn bonds, forming 1D large channels based on [Mn4Sn16] 20-membered rings along the b-axis, which are occupied by the rare earth atoms. Electronic structure calculations based on density functional theory (DFT) for idealized “RE3MnSn5” model indicate that these compounds are metallic, which are in accordance with the results from temperature-dependent resistivity measurements. 相似文献
7.
S. Havelia 《Journal of solid state chemistry》2009,182(7):1603-4554
Thin films of RE2Ti2O7 (RE=La, Nd, Sm, Gd) were deposited on single crystal SrTiO3 (110) substrates at 900 °C using pulsed laser deposition. X-ray diffraction (XRD) results showed sharp (00k) peaks (in θ-2θ scans) with narrow rocking curves (ω-scan peak widths of 0.4-0.9°), indicating that all compositions adopted the (110)-layered perovskite structure. While this is the stable structure for RE=La and Nd, it is metastable for RE=Sm and Gd. The metastable compounds are formed directly through epitaxial stabilization at these high temperatures and are shown to be isostructural to monoclinic La2Ti2O7. The a, b, and c lattice parameters decreased monotonically with decreasing size of the RE cation, while the monoclinic angle remained fairly constant. The epitaxial relationship between the (110)-layered RE2Ti2O7 films and the SrTiO3(110) substrate was found by XRD and transmission electron microscopy to be . The single-phase, metastable, epitaxial, 100 nm thick films maintained the layered perovskite structure even after annealing at 900 °C for two hours in 200 Torr of oxygen. 相似文献
8.
Volodymyr Babizhetskyy Hansjürgen Mattausch Kurt Hiebl Régis Gautier 《Journal of solid state chemistry》2008,181(8):1882-1890
The ternary rare-earth metal boride carbides RE15B6C20 (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their crystal structures were determined from single-crystal X-ray diffraction data. Both crystallize in the space group P1¯, Z=1, a=8.3431(8) Å, b=9.2492(9) Å, c=8.3581(8) Å, α=84.72(1)°, β=89.68(1)°, γ =84.23(1)° (R1=0.041 (wR2=0.10) for 3291 reflections with Io>2σ(Io)) for Pr15B6C20, and a=8.284(1) Å, b=9.228(1) Å, c=8.309(1) Å, α=84.74(1)°, β=89.68(1)°, γ=84.17(2)° (R1=0.033 (wR2=0.049) for 2970 reflections with Io>2σ(Io)) for Nd15B6C20. Their structure consists of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B2C4 finite chains, disordered C3 entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE3+)15([B2C4]6−)3([C3]4−)2(C4−)2·11ē. Accordingly, density functional theory calculations indicate that the compounds are metallic. Both structural arguments as well as energy calculations on different boron vs. carbon distributions in the B2C4 chains support the presence of a CBCCBC unit. Pr15B6C18 exhibits antiferromagnetic order at TN=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd15B6C18 is a ferromagnet below TC≈40 K. 相似文献
9.
V Meignen A Lafond Y Moëlo C Guillot-Deudon A Meerschaut 《Journal of solid state chemistry》2004,177(8):2810-2817
Two new compounds, La5Ti2MS5O7 (M=Cu, Ag) were synthesized and their structures solved from single crystal X-ray data. Both compounds are isotypic. They crystallize in the orthorhombic system (space group Pnma, Z=4) with lattice constants a=19.423(1) Å, b=3.9793(2) Å, c=18.1191(9) Å for La5Ti2CuS5O7, and a=19.593(2) Å, b=3.9963(1) Å, and c=18.2973(15) Å for La5Ti2AgS5O7. The structure of these compounds is built from fragments of the rock-salt, perovskite and fluorite types and a clear anionic segregation of the anions appears in the structure. La5Ti2CuS5O7 and La5Ti2AgS5O7 exhibit an orange-yellow color and measurement of their optical band gap gave 2.02 and 2.17 eV, respectively. 相似文献
10.
Marina A Zhuravleva 《Journal of solid state chemistry》2003,173(2):280-292
The RE3Ga9Ge compounds (RE=Y, Ce, Sm, Gd and Yb) were synthesized at 850°C in quantitative yield from reactions containing excess liquid Ga. The orthorhombic crystal structure is characterized by a unique three-dimensional open Ga framework with parallel straight tunnels. In the tunnels, inserted are arrays of the RE atoms together with interpenetrated monoatomic RE-Ga-Ge planes. A complex disordered arrangement of the RE and Ga atoms is observed in the monoatomic plane. Depending on the extent of disorder, the crystal structure could be presented either in a sub-cell (no ordering) or in a super-cell (partial ordering). Single-crystal X-ray data for Ce3Ga9Ge sub-structure: space group Immm, Z=2, cell parameters a=4.3400(12) Å; b=10.836(3) Å; and c=11.545(3) Å; super-structure: space group Cmma, Z=8, cell parameters a=8.680(3) Å; b=23.090(7) Å; and c=10.836(3) Å. The refinement based on the full-matrix least squares on Fo2[I>2σ(I)] converged to final residuals R1/wR2=0.0226/0.0528 and 0.0729/0.1569 for the sub- and super-structures, respectively. The relationship between the disordered sub-structure and partially ordered super-structure is discussed. Magnetic susceptibility measurements show Curie-Weiss behavior at the temperatures above 30 K with the negative Weiss constants Θ=−49(1) and−7.7 K for Gd and Ce analogs, respectively. An antiferromagnetic transition is observed in the Gd analog at TN=26.1 K. The μeff obtained for both analogs is close to the RE3+ free-ion value. 相似文献
11.
Andriy V. Tkachuk 《Journal of solid state chemistry》2006,179(5):1506-1512
The ternary rare-earth cadmium antimonides RECd1−xSb2 (RE=La, Ce, Pr, Nd, Sm) were prepared by reaction of the elements at 1000 °C. The presence of Cd defects, previously found for LaCd0.700(5)Sb2 and CeCd0.660(4)Sb2, has been confirmed by single-crystal X-ray diffraction studies for the isotypic compounds PrCd0.665(3)Sb2, ), NdCd0.659(3)Sb2, ), and SmCd0.648(3)Sb2, ). These compounds adopt the HfCuSi2-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). The electrical and magnetic properties of samples with nominal composition RECd0.7Sb2 were investigated. All exhibit metallic behaviour, but CeCd0.7Sb2 undergoes an abrupt drop in its electrical resistivity below 3 K. LaCd0.7Sb2 exhibits temperature-independent Pauli paramagnetism and SmCd0.7Sb2 displays van Vleck paramagnetism. The remaining compounds obey the modified Curie-Weiss law at high temperatures. CeCd0.7Sb2 undergoes ferromagnetic ordering below 3 K, reaching a saturation magnetization of ∼1.0 μB, whereas PrCd0.7Sb2 and NdCd0.7Sb2 remain paramagnetic down to 2 K. 相似文献
12.
Ioana Vidican 《Journal of solid state chemistry》2003,170(2):203-210
Single crystals of K3RESi2O7 (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K3RESi2O7 that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K3LuSi2O7, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K3LuSi2O7 crystallizes in space group P63/mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P63/mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K3GdSi2O7); a=9.88730(10) Å, c=14.3856(3) Å, (K3TbSi2O7); a=9.8673(2) Å, c=14.3572(4) Å, (K3DySi2O7); a=9.8408(3) Å, c=14.3206(6) Å, (K3HoSi2O7); a=9.82120(10) Å, c=14.2986(2) Å, (K3ErSi2O7); a=9.80200(10) Å, c=14.2863(4) Å, (K3TmSi2O7); a=9.78190(10) Å, c=14.2401(3) Å, (K3YbSi2O7). The optical properties of the silicates were investigated and K3TbSi2O7 was found to fluoresce in the visible. 相似文献
13.
Single crystals of the oxidephosphates TiIIITiIV3O3(PO4)3 (black), CrIII4TiIV27O24(PO4)24 (red-brown, transparent), and FeIII4TiIV27O24(PO4)24 (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [TiIIITiIV3O3(PO4)3: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R1=0.029, wR2=0.084, 6055 independent reflections, 301 variables; CrIII4TiIV27O24(PO4)24: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R1=0.037, wR2=0.097, 1524 independent reflections, 111 variables; FeIII4TiIV27O24(PO4)24: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R1=0.049, wR2=0.140, 1240 independent reflections, 112 variables). For TiIIITiIVO3(PO4)3 a well-ordered structure built from dimers [TiIII,IV2O9] and [TiIV,IV2O9] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr4Ti27O24(PO4)24 and Fe4Ti27O24(PO4)24, consisting of dimers [MIIITiIVO9] and [TiIV,IV2O9], monomeric [TiIVO6] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs TiIII4TiIV27O24(PO4)24 (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates MIII4TiIV27O24(PO4)24 (MIII: Cr, Fe). The UV/vis spectrum of Cr4Ti27O24(PO4)24 reveals a rather small ligand-field splitting Δo=14,370 cm−1 and a very low nephelauxetic ratio β=0.72 for the chromophores [CrIIIO6] within the dimers [CrIIITiIVO9]. 相似文献
14.
The crystal structures of the new ternary compounds LaCuMg4 and TbCuMg4 were studied by X-ray powder diffraction and single-crystal methods, respectively. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for examining microstructure and phase composition. LaCuMg4 crystallizes in the UCoAl4 structure type (space group P6¯2m, Pearson code hP18, a=1.03911(1), c=0.45126(1) nm, Z=3, RF=0.0654), while TbCuMg4 exhibits a new structure (space group Cmmm, Pearson code oS48, a=1.35797(6), b=2.03333(9), c=0.39149(2) nm, Z=8, wR2=0.0426). Both structures represent a family of two-layer compounds. All interatomic distances indicate metallic type bonding. The structural peculiarities of these compounds and their relations are discussed. 相似文献
15.
Laura DeakinMichael J. Ferguson Michael J. SpragueArthur Mar R.D. SharmaColin H.W. Jones 《Journal of solid state chemistry》2002,164(2):292-300
The nonstoichiometric rare-earth tin antimonides RESnxSb2 (RE=La, Ce, Pr, Nd, Sm) were characterized by 119Sn Mössbauer spectroscopy and their transport and magnetic properties were measured. The presence of nearly zero-valent Sn is suggested by the similarity of the 119Sn Mössbauer parameters in LaSnxSb2 (0.1≤x≤0.7) to those of elemental β-Sn. All RESn0.7Sb2 compounds exhibit metallic behavior. CeSn0.7Sb2 and NdSn0.7Sb2 show drops in resistivity below 8 K; this is attributed to a transition to a magnetically ordered state. At 25 K, CeSn0.7Sb2 also displays a resistivity minimum characteristic of ordered Kondo lattices. Magnetic studies indicate that, below 4 K, CeSnxSb2 (x=0.5, 0.7) orders ferromagnetically, whereas NdSnxSb2 (x=0.5, 0.7) orders antiferromagnetically and undergoes a metamagnetic transition at HC=5.5 T and 2 K. Neither PrSnxSb2 nor SmSnxSb2 (x=0.5, 0.7) displays long-range magnetic ordering above 2 K. 相似文献
16.
Karolina Kazmierczak 《Journal of solid state chemistry》2011,184(5):1221-1226
The lanthanide sulphate octahydrates Ln2(SO4)3·8H2O (Ln=Ho, Tm) and the respective tetrahydrate Pr2(SO4)3·4H2O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln2(SO4)3·8H2O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, aHo=13.4421(4) Å, bHo=6.6745(2) Å, cHo=18.1642(5) Å, βHo=102.006(1) Å3 and aTm=13.4118(14) Å, bTm=6.6402(6) Å, cTm=18.1040(16) Å, βTm=101.980(8) Å3), Pr2(SO4)3·4H2O adopts space group P21/n (a=13.051(3) Å, b=7.2047(14) Å, c=13.316(3) Å, β=92.55(3) Å3). The vibrational and optical spectra of Ho2(SO4)3·8H2O and Pr2(SO4)3·4H2O are also reported. 相似文献
17.
Yuriy B. Tyvanchuk Ute Ch. Rodewald Rainer Pöttgen 《Journal of solid state chemistry》2008,181(12):3223-3228
The ternary copper indides RE2CuIn3≡RECu0.5In1.5 (RE=Ce, Pr, Nd, Sm and Gd) were synthesized from the elements in sealed tantalum tubes in an induction furnace. They crystallize with the CaIn2-type structure, space group P63/mmc, with a statistical occupancy of copper and indium on the tetrahedral substructure. These indides show homogeneity ranges RECuxIn2−x. Single crystal structure refinements were performed for five crystals: CeCu0.66In1.34 (a=479.90(7) pm, c=768.12(15) pm), PrCu0.52In1.48 (a=480.23(7) pm, c=759.23(15) pm), NdCu0.53In1.47 (a=477.51(7) pm, c=756.37(15) pm), SmCu0.46In1.54 (a=475.31(7) pm, c=744.77(15) pm), and GdCu0.33In1.67 (a=474.19(7), c=737.67(15) pm). Temperature-dependent susceptibility measurements show antiferromagnetic ordering at TN=4.7 K for Pr2CuIn3 and Nd2CuIn3 and 15 K for Sm2CuIn3. Fitting of the susceptibility data of the samarium compound revealed an energy gap ΔE=39.7(7) K between the ground and the first excited levels. 相似文献
18.
Victoria V Chernaya Roman V Shpanchenko Evgeny V Antipov Elena N Morozova Joke Hadermann Christoph Geibel 《Journal of solid state chemistry》2004,177(8):2875-2880
Two new complex vanadyl(IV)phosphates Na2MVO(PO4)2 (M=Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na2SrVO(PO4)2 was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a=10.5233(3) Å, b=6.5578(2) Å, c=10.0536(3) Å and a=10.6476(3) Å, b=6.6224(2) Å, c=10.2537(3) Å for Ca and Sr, respectively; S.G. Pnma, Z=4. The compounds have a three-dimensional structure consisting of V4+O6 octahedra connected by PO4 tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with θ=12 and 5 K for Ca and Sr phases, respectively. 相似文献
19.
Seong-Ju Hwang 《Journal of solid state chemistry》2004,177(10):3640-3649
The quaternary alkali-metal gallium selenostannates, Na2−xGa2−xSn1+xSe6 and AGaSnSe4 (A=K, Rb, and Cs), were synthesized by reacting alkali-metal selenide, Ga, Sn, and Se with a flame melting-rapid cooling method. Na2−xGa2−xSn1+xSe6 crystallizes in the non-centrosymmetric space group C2 with cell constants a=13.308(3) Å, b=7.594(2) Å, c=13.842(3) Å, β=118.730(4)°, V=1226.7(5) Å3. α-KGaSnSe4 crystallizes in the tetragonal space group I4/mcm with a=8.186(5) Å and c=6.403(5) Å, V=429.1(5) Å3. β-KGaSnSe4 crystallizes in the space group P21/c with cell constants a=7.490(2) Å, b=12.578(3) Å, c=18.306(5) Å, β=98.653(5)°, V=1705.0(8) Å3. The unit cell of isostructural RbGaSnSe4 is a=7.567(2) Å, b=12.656(3) Å, c=18.277(4) Å, β=95.924(4)°, V=1741.1(7) Å3. CsGaSnSe4 crystallizes in the orthorhombic space group Pmcn with a=7.679(2) Å, b=12.655(3) Å, c=18.278(5) Å, V=1776.1(8) Å3. The structure of Na2−xGa2−xSn1+xSe6 consists of a polar three-dimensional network of trimeric (Sn,Ga)3Se9 units with Na atoms located in tunnels. The AGaSnSe4 possess layered structures. The compounds show nearly the same Raman spectral features, except for Na2−xGa2−xSn1+xSe6. Optical band gaps, determined from UV-Vis spectroscopy, range from 1.50 eV in Na2−xGa2−xSn1+xSe6 to 1.97 eV in CsGaSnSe4. Cooling of the melts of KGaSnSe4 and RbGaSnSe4 produces only kinetically stable products. The thermodynamically stable product is accessible under extended annealing, which leads to the so-called γ-form (BaGa2S4-type) of these compounds. 相似文献
20.
Edurne S. Larrea José L. Pizarro Teófilo Rojo 《Journal of solid state chemistry》2007,180(5):1686-1697
The Mn5−xCox(HPO4)2(PO4)2(H2O)4 (x=1.25, 2, 2.5, 3) finite solid solution has been synthesized by mild hydrothermal conditions under autogeneous pressure. The phases crystallize in the C2/c space group with Z=4, belonging to the monoclinic system. The unit-cell parameters obtained from single crystal X-ray diffraction are: a=17.525(1), b=9.0535(6), c=9.4517(7) Å, β=96.633(5) ° being R1=0.0436, wR2=0.0454 for Mn75Co25; a=17.444(2), b=9.0093(9), c=9.400(1) Å, β=96.76(1) ° being R1=0.0381, wR2=0.0490 for Mn60Co40; a=17.433(2), b=8.9989(9), c=9.405(1) Å, β=96.662(9) ° being R1=0.0438, wR2=0.0515 for Mn50Co50 and a=17.4257(9), b=8.9869(5), c=9.3935(5) Å, β=96.685(4) ° being R1=0.0296, wR2=0.0460 for Mn40Co60. The structure consists of a three dimensional network formed by octahedral pentameric entities (Mn,Co)5O16(H2O)6 sharing vertices with the (PO4)3− and (HPO4)2− tetrahedra. The limit of thermal stability of these compounds is, approximately, 165 °C, near to this mean temperature the phases loose their water content in two successive steps. IR spectra show the characteristic bands of the water molecules and the phosphate and hydrogen-phosphate oxoanions. The diffuse reflectance spectra are consistent with the presence of MO6 octahedra environments in slightly distorted octahedral geometry, except for the M(3)O6 octahedron which presents a remarkable distortion and so a higher Dq parameter. The mean value for the Dq and B-Racah parameter for the M(1),(2)O6 octahedra is 685 and 850 cm−1, respectively. These parameters for the most distorted M(3)O6 polyhedron are 825 and 880 cm−1, respectively. The four phases exhibit antiferromagnetic couplings as the major magnetic interactions. However, a small spin canting phenomenon is observed at low temperatures for the two phases with major content in the anisotropic-Co(II) cation. 相似文献