Search

Exploratory studies in the systemsA–Al–Sn (A= K and Rb) yielded the clathrates K8AlxSn46–x(potassium aluminium stannide) and Rb8AlxSn46–x(rubidium aluminium stannide), both with the cubic type-I structure (space groupPm\overline{3}n, No. 223;a≃ 12.0 Å). The Al:Sn ratio is close to the idealizedA8Al8Sn38composition and it is shown that it can be varied slightly, in the range ofca±1.5, depending on the experimental conditions. Both the (Sn,Al)20and the (Sn,Al)24cages in the structure are fully occupied by the guest alkali metal atoms,i.e.K or Rb. TheA8Al8Sn38formula has a valence electron count that obeys the valence rules and represents an intrinsic semiconductor, while the experimentally determined compositionsA8Al8±xSn38∓xsuggest the synthesized materials to be nearly charge-balanced Zintl phases,i.e.they are likely to behave as heavily dopedp- orn-type semiconductors.

Studies in the systems Cs–Na–Cu–Si and Cs–Na–Zn–Si yielded the novel clathrates Cs8Na16(Cu,Si)136 and Cs8Na16(Zn,Si)136, both with the cubic type-II structure [space group Fd3m (no. 227), Pearson symbol cF160]. The structures of the title compounds were established from single-crystal X-ray diffraction methods, confirming the complete ordering of the Cs and Na guest atoms. The framework-building Si atoms are found to be randomly substituted by Cu atoms on framework site 96g, exclusively. In the structure of Cs8Na16(Zn,Si)136, the refinements indicate that the Zn and Si atoms co-occupy two of the three framework sites with notable preference for site 96g over site 32e. The corresponding refined compositions and unit cell parameters are as follows: Cs8Na16Cu3.8Si132.2(1) [a = 14.7583(15) A]; Cs8Na16Zn6.9Si129.1(1) [a = 14.7682(5) A], respectively. The type-II clathrates can be obtained only from experiments employing both Na and Cs, whereas work in the ternary Cs-Cu-Si, Cs-Zn-Si, Na-Cu-Si, and Na-Zn-Si systems failed to yield any clathrate phases. At the same conditions, exploratory studies in the K-Zn-Si and Rb-Zn-Si systems provided evidence that type-I clathrates are favored.

Zintl phases are renowned for their diverse crystal structures with rich structural chemistry and have recently exhibited some remarkable heat- and charge-transport properties. The ternary bismuthidesRELi3Bi2(RE= La–Nd, Sm, Gd, and Tb) (namely, lanthanum trilithium dibismuthide, LaLi3Bi2, cerium trilithium dibismuthide, CeLi3Bi2, praseodymium trilithium dibismuthide, PrLi3Bi2, neodymium trilithium dibismuthide, NdLi3Bi2, samarium trilithium dibismuthide, SmLi3Bi2, gadolinium trilithium dibismuthide, GdLi3Bi2, and terbium trilithium dibismuthide, TbLi3Bi2) were synthesized by high-temperature reactions of the elements in sealed Nb ampoules. Single-crystal X-ray diffraction analysis shows that all seven compounds are isostructural and crystallize in the LaLi3Sb2type structure in the trigonal space groupP\overline{3}m1 (Pearson symbolhP6). The unit-cell volumes decrease monotonically on moving from the La to the Tb compound, owing to the lanthanide contraction. The structure features a rare-earth metal atom and one Li atom in a nearly perfect octahedral coordination by six Bi atoms. The second crystallographically unique Li atom is surrounded by four Bi atoms in a slightly distorted tetrahedral geometry. The atomic arrangements are best described as layered structures consisting of two-dimensional layers of fused LiBi4tetrahedra and LiBi6octahedra, separated by rare-earth metal cations. As such, these compounds are expected to be valance-precise semiconductors, whose formulae can be represented as (RE3+)(Li1+)3(Bi3−)2.

Systematic studies in the systems Cs–Na–Ga–Si, Rb–Na–Ga–Si, and Rb–Na–Zn–Si yielded the novel type-I clathrates with refined compositions Cs6Na2Ga8.25Si37.75(3), Rb6.34Na1.66(2)Ga8.02Si37.98(3), and Rb5.20Na2.80(4)Zn3.85Si42.15(2) (cubic, ), as well as the type-II clathrates with formulae Cs8Na16Ga22.7Si113.3(1), Rb8.4Na15.6(1)Ga19.6Si116.4(1), and Rb8Na16Zn8.4Si127.6(1) (cubic, ). In each system, the type-I and -II compounds are always co-crystallizing, irrespective of the reaction conditions. The structures derived from single-crystal X-ray diffraction confirm complete ordering of Cs and Na atoms, and nearly complete ordering of the Rb and Na guest atoms. The framework-building Si atoms are randomly substituted by Ga or Zn atoms on all framework sites with notable difference in the substitution patterns between the type-I and type-II structure. This, and other details of the crystal chemistry are discussed in this paper.

Reported are the synthesis and the structural characterization of an extended family of rare-earth metal–lithium–antimonides with the formula RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho). They crystallize in the trigonal space group P3{sup ¯}m1 (No. 164, Pearson symbol hP6) with a structure, best viewed as a filled derivative of the common CaAl{sub 2}Si{sub 2} structure type (ternary variant of α-La{sub 2}O{sub 3}). Across the series, the lattice parameters monotonically decrease, following the lanthanide contraction. Temperature-dependent magnetic susceptibility measurements for CeLi{sub 3}Sb{sub 2}, PrLi{sub 3}Sb{sub 2} and TbLi{sub 3}Sb{sub 2} reveal paramagnetic behavior in the high temperature range, and the obtained effective moments are consistent with the expected ones for the free-ion RE{sup 3+} ground state. Possible ferromagnetic ordering for PrLi{sub 3}Sb{sub 2} and antiferromagnetic ordering for TbLi{sub 3}Sb{sub 2} are observed in the low temperature range (below 20 K). Tight-binding muffin-tin orbital electronic band structure calculations for LaLi{sub 3}Sb{sub 2} are presented and discussed as well. - Graphical abstract: The large family of rare-earth metal–lithium–antimonides with the formula RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho) crystallize in the trigonal space group P3{sup ¯}m1 (No. 164, Pearson symbol hP6) with a structure that is a filled derivative of the CaAl{sub 2}Si{sub 2} structuremore » type (ternary variant of α-La{sub 2}O{sub 3}). Display Omitted - Highlights: • RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho) constitute an extended family of rare-earth metal–lithium–antimonides. • The layered structure is a filled derivative of the common CaAl{sub 2}Si{sub 2} structure type. • The valence electron count follows the Zintl–Klemm rules. • Electronic band structure calculations for LaLi{sub 3}Sb{sub 2} indicate small band-gap semiconducting behavior.« less

Reported are two series of tin-based clathrates—A8Cu2.67Sn43.33 and A8Zn4Sn42 (A = K, Rb, Cs)—crystallizing in the cubic type-I structure. The six new compounds have been obtained in quantitative yields and have been characterized by single-crystal X-ray diffraction. Copper and zinc randomly substitute tin on only one of the three framework sites, 6c, while the remaining two sites 16i and 24k are exclusively occupied by tin. The alkali metals reside in the two types of cages in the structure—the 20-atom dodecahedra and the 24-atom tetrakaidecahedra. According to the structure refinements, both cages are completely filled; in the bigger tetrakaidecahedron, the smaller K and Rb atoms are displaced off its center, whereas the larger Cs atoms are located at the center. These findings are presented and discussed; preliminary results from measurements of the Seebeck coefficients (300–500 K) and the electrical resistivity (100–400 K) are presented as well.

Three new europium pnictides Eu2ZnP2, Eu2Zn2P3 and Eu2Cd2As3 have been synthesized and their structures were determined by single-crystal X-ray diffraction. Eu2ZnP2 is isotypic with Yb2CdSb2 (Cmc21 (No. 36); cell parameters a=4.1777(7) A, b=15.925(3) A, c=7.3008(12) A), while the latter two compounds crystallize with the Ba2Cd2Sb3 structure type (C2/m (No. 12); cell parameters a=15.653(5)/16.402(1) A, b=4.127(1)/4.445(4) A, c=11.552(4)/12.311(1) A and β=126.647(4)/126.515(7)° for Eu2Zn2P3 and Eu2Cd2As3, respectively). Magnetic susceptibility measurements in the interval 5–300 K confirm paramagnetic behavior and effective magnetic moments characteristic of Eu2+ ([Xe] 4f7) ground states. Temperature-dependent electrical conductivity measurements also prove that Eu2Cd2As3 is a semiconducting compound with a narrow band gap of 0.059 eV below 100 K. According to TG/DSC analyses, Eu2Cd2As3 starts to decompose at about 950 K.

For a very long time, Ba(16)Ga(32)Sn(104) has been the sole representative of tin clathrates with the type II structure. Herein, we present several new members of this structural family: Cs(8)Ba(16)Ga(39.7(3))Sn(96.3(3)), Rb(9.9(5))Ba(13.3(2))Ga(36.4(3))Sn(99.6(3)), and K(2.0(4))Ba(14.0(4))Ga(30.4(2))Sn(105.6(4)). The successful synthesis of these novel compounds was facilitated through the use of alkali and alkaline-earth metals, which selectively fill the available cages.

The here reported compounds of the isotypic series Ln

International audience; We investigated the high-temperature thermoelectric properties of Ga:ZnO bulk compounds, synthesized using a simple and scalable solid-state process. The effects of a low gallium content (x ≤ 0.04 in Zn1−xGaxO1+x/2) on the structural features and electrical/thermal properties are reviewed. Transmission electron microscopy analyses showed that 2D, nonperiodic defects had formed from a doping content as low as x = 0.01 Ga. The structural description of these nanoscale interfaces is, for the first time, carefully investigated in such low-Ga-content samples by HAADF-STEM analyses combined with structural modeling. It was found that the formation of head-to-head inversion twin (h-IT) boundaries and tail-to tail inversion boundaries (t-IB) in the bulk compounds is responsible for strong phonon scattering, while maintaining relatively good electrical conductivity and thereby enhancing the thermoelectric properties. The absolute value of the Seebeck coefficient decreases abruptly from 475 μV/K for x = 0 down to 60 μV/K for x = 0.005 at 350 K. At the same time, the electrical resistivity drops from 1 ohm cm for x = 0 to 1.7 × 10–3 ohm cm for x = 0.005. For higher Ga additions (x > 0.01), the increase in electrical resistivity is likely linked to the formation of interface defects at a larger extent in the wurtzite structure. The thermal conductivity also drops sharply with the increase in the Ga content from ∼33 W/m K for x = 0 to ∼8 for x = 0.04 at 350 K. This study is progress toward the synthesis of other thermoelectric materials where nanoscale interfaces in bulk compounds provide tremendous opportunities for further enhancing both the phonon scattering and the overall figure of merit.

Ceramics based on Sr

Investigations in the Cu-rich parts of the ternary systems A–Cu–Tt (A = Ca, Sr, Ba, Eu, Yb; Tt = Si, Ge, Sn) were carried out using the molten flux method. The results indicate that using tin as a flux, several stannides with a general formula ACu9Sn4 (A = Ca, Sr, Ba, and Eu) can be readily synthesized. Their structures (space group I4/mcm, Pearson symbol tI56) are ordered ternary variants of the cubic NaZn13 structure type. In the corresponding germanium and silicon systems, only the solid solutions BaCu9–xGe4+x and BaCu9–xSi4+x (x ≈ 0.5) can be obtained from eutectic Cu:Tt mixtures with compositions approximately 2:1. Their structures are formally isotypic with the CeNi8.5Si4.5 structure type, a partially ordered variant of the same NaZn13 structure. In the remaining systems A–Cu–Tt (A = Ca, Sr, Eu, Yb; Tt = Si, Ge), the known ACu2Tt2 phases (space group I4/mmm, Pearson symbol tI10) with the ThCr2Si2 structure type were found to be the most frequently observed products. In this article we discuss the subtleties of each structure with regard to the synthetic route; the similarities and the differences in the syntheses, and the structure refinements among the studied compounds are compared and contrasted. The structure of SrCu2Ge2 was also re-assessed.

The new quinary fluoride-rich rubidium scandium oxosilicate Rb3Sc2F5Si4O10 was obtained from mixtures of RbF, ScF3, Sc2O3 and SiO2 in sealed platinum ampoules after seventeen days at 700 °C. The colourless compound crystallises orthorhombically in space group Pnma with a = 962.13(5), b = 825.28(4), c = 1838.76(9) pm and Z = 4. For the oxosilicate partial structure, [SiO4]4– tetrahedra are connected in (001) by vertex-sharing to form corrugated unbranched vierer single layers {[Si4O10]4–} (d(Si–O) = 158–165 pm, ∠(O–Si–O) = 103–114°, ∠(Si–O–Si) = 125–145°) containing six-membered rings. Similar oxosilicate layers with 63-net topology are well-known for the mineral group of micas or in sanbornite Ba2Si4O10. Regarding other systems, identical tetrahedral layers can be found in the synthetic borophosphate Mg(H2O)2[B2P2O8(OH)2]·H2O. The Sc3+ cations are coordinated octahedrally by four F– and two O2– anions. These cis-[ScF4O2]5– octahedra (d(Sc–F) = 200–208 pm, d(Sc–O) = 202–205 pm) share one equatorial and two apical F– anions with others to build up slightly corrugated {[Sc2FFO]7–} double chains along [010]. These are linked with the oxosilicate layers via two oxygen vertices to construct a three-dimensional framework with cavities apt to host the three crystallographically independent Rb+ cations with coordination numbers of eleven, twelve and thirteen.

In the quaternary system Cs / Nd / Si / O, two new representatives, the phyllo-oxosilicate Cs3NdSi8O19 and the tecto-oxosilicate Cs6Nd2Si21O48, were synthesized by CsF-flux-supported solid-state reactions between Nd2O3 and SiO2. The first one, Cs3NdSi8O19 (orthorhombic, Cmcm (no. 63), a = 705.74(5), b = 2712.85(19), c = 1163.72(8) pm, Z = 4), is not isotypic to the related scandium compound Cs3ScSi8O19. The [SiO4]4− tetrahedra (d(Si4+ -O2−) = 156 -163 pm) in the structure of Cs3NdSi8O19 are connected via common corners to form corrugated, loop-branched double layers containing four- and eight-membered rings in the (010) plane and eight-membered rings along [001]. Each of the eight-membered ellipses emerging along [100] is additionally loopbranched by two four-membered chains. The oxosilicate double layers are cross-linked by vertexsharing via otherwise isolated [NdO6]9− octahedra (d(Nd3+-O2-)= 232 - 234 pm) to build up a three-dimensional framework. Also in between the oxosilicate double layers, the (Cs1)+ cations are located on the 8 f site. Each of the octagonal channels along [001] hosts one (Cs3)+ and two (Cs2)+ cations, which both reside at only partially occupied sites (8g and 8 f , respectively) and disorder, because otherwise too short Cs+ ・ ・ ・ Cs+ distances would occur. The second compound, Cs6Nd2Si21O48, crystallizes also in an orthorhombic space group (Pmmn (no. 59), a = 2189.24(15), b = 731.92(5), c = 1593.61(11) pm, Z = 2). Starting from a loop-branched single layer containing five- and eight-membered rings, a three-dimensional framework of vertex-shared [SiO4]4− tetrahedra (d(Si4+-O2−) = 149 - 164 pm) built up, in which the Si-O distances range from 149 to 164 pm within a broad range. In certain cavities, one kind of Nd3+, but four kinds of Cs+ cations (here, all sites with full occupation) are embedded. Also surrounded by only six O2− anions just like in the first case, the Nd3+ cations (d(Nd3+-O2−) = 233 - 237 pm) exhibit an unusually small, but not unknown coordination sphere for this relatively large lanthanoid(III) cation

La4B14O27: A Lanthanum ultra-Oxoborate with a Framework Structure Single crystals of La4B14O27 could be synthesized by the reaction of La2O3, LaCl3 and B2O3 with an access of CsCl as fluxing agent in gastightly sealed platinum ampoules within twenty days at 710 °C and appear as colourless, transparent and waterresistant platelets. The new lanthanum oxoborate La4B14O27 (monoclinic, C2/c; a = 1120.84(9), b = 641.98(6), c = 2537.2(2) pm, β = 100.125(8)°; Z = 4) is built of a three-dimensional boron-oxygen framework containing seven crystallographically different boron atoms. Four of these B3+ cations are surrounded by four O2− anions tetrahedrally, whereas the other three have only three oxygen neighbours with nearly plane triangular coordination figures. Three of the [BO4]5− tetrahedra form [B3O9]9− rings by cyclic vertex-condensation, which are further linked via [BO3]3− units to infinite layers. Two of these layers connect via one [B2O7]8− unit of two corner-shared [BO4]5− tetrahedra to double layers, which themselves build up a three-dimensional framework together with chains consisting of two [BO4]5− tetrahedra and one [BO3]3− triangle. One of the two crystallographically independent La3+ cations (La1) is surrounded by ten O2− anions and resides within the oxoborate double layers. (La2)3+ shows a (8+2)-fold coordination of O2− anions and occupies channels along the [110] direction.

Synthesis and Crystal Structure of the Fluoride ino-Oxosilicate Cs2YFSi4O10 The novel fluoride oxosilicate Cs2YFSi4O10 could be synthesized by the reaction of Y2O3, YF3 and SiO2 in the stoichiometric ratio 2 : 5 : 3 with an excess of CsF as fluxing agent in gastight sealed platinum ampoules within seventeen days at 700 °C. Single crystals of Cs2YFSi4O10 appear as colourless, transparent and water-resistant needles. The characteristic building unit of Cs2YFSi4O10 (orthorhombic, Pnma (no. 62), a = 2239.75(9), b = 884.52(4), c = 1198.61(5) pm; Z = 8) comprises infinite tubular chains of vertex-condensed [SiO4]4− tetrahedra along [010] consisting of eight-membered half-open cube shaped silicate cages. The four crystallographically different Si4+ cations all reside in general sites 8d with Si–O distances from 157 to 165 pm. Because of the rigid structure of this oxosilicate chain the bridging Si–O–Si angles vary extremely between 128 and 167°. The crystallographically unique Y3+ cation (in general site 8d as well) is surrounded by four O2− and two F− anions (d(Y–O) = 221–225 pm, d(Y–F) = 222 pm). These slightly distorted trans-[YO4F2]7− octahedra are linked via both apical F− anions by vertex-sharing to infinite chains along [010] (∢(Y–F–Y) = 169°, ∢(F–Y–F) = 177°). Each of these chains connects via terminal O2− anions to three neighbouring oxosilicate chains to build up a corner-shared, three-dimensional framework. The resulting hexagonal and octagonal channels along [010] are occupied by the four crystallographically different Cs+ cations being ten-, twelve-, thirteen- and fourteenfold coordinated by O2− and F− anions (viz.[(Cs1)O10]19−, [(Cs2)O10F2]21−, [(Cs3)O12F]24−, and [(Cs4)O12F2]25− with d(Cs–O) = 309–390 pm and d(Cs–F) = 360–371 pm, respectively).

This study focuses on the exploration of the ternary systems A–Li–Pn with A = Ca–Ba, Eu and Yb and Pn = As–Bi resulting in the extensions of the ALiPn series (A = Ca, Sr, Eu and Yb; Pn = As–Bi; orthorhombic Pnma) with the MgSrSi structure type and of the A3Li4Pn4 family (A = Ba, Eu; Pn = As–Bi; orthorhombic Immm) with the Zr3Cu4Si4 structure type, as well as the novel compound Eu4Li7Bi6 (monoclinic, C2/m) with its own structure type. The relevant structural relationships are discussed. The building blocks and the topology of the polyanionic networks among the three different structures are compared side-by-side. Electronic band structure calculations for EuLiSb, Eu3Li4Sb4 and Eu4Li7Bi6 are discussed; the magnetic susceptibility and resistivity of single-crystalline Eu3Li4Sb4 are also presented.

Studies in the Rb–Eu–In–Ge system confirm the existence of the phase Rb8−xEux(In,Ge)46(0.6 ≤x≤ 1.8), crystallizing with the cubic clathrate type-I structure. The In and Ge content can be varied, concomitant with changes in the Rb–Eu ratio. Two of the three framework sites are occupied by statistical mixtures of Ge and In atoms, while the site with the lowest multiplicity is taken by the In atoms only. Based on the three refined formulae [heptarubidium europium nonaindium heptatriacontagermanide, Rb7.39(3)Eu0.61(3)In8.88(5)Ge37.12(5), and two forms of hexarubidium dieuropium decaindium hexatriacontagermanide, Rb6.30(3)Eu1.70(3)In9.76(4)Ge36.24(4)and Rb6.24(2)Eu1.76(2)In10.16(5)Ge35.84(5)] and the explored different synthetic routes, it can be suggested that the known ternary phase Rb8In8Ge38and the hypothetical quaternary phase Rb6Eu2In10Ge36represent the boundaries of the homogeneity range. In the former limiting composition, both the (Ge,In)20and the (Ge,In)24cages are fully occupied by Rb atoms only, whereas Rb6Eu2In10Ge36has Rb atoms encapsulated in the larger tetrakaidecahedra, with Eu atoms filling the smaller pentagonal dodecahedra. For the solid solutions Rb8−xEux(In,Ge)46, Rb and Eu are statistically disordered in the dodecahedral cage, and the tetrakaidecahedral cage is only occupied by Rb atoms.

In the crystal structure of Y4F2[Si2O7][SiO4], three fundamental building blocks are present, viz. anionic disilicate and orthosilicate units ([Si2O7](6-) and [SiO4](4-)) and cationic [F2Y4](10+) entities. The latter are built up by two [FY3](8+) triangles sharing a common edge. The four crystallographically independent Y(3+) cations display coordination numbers of eight for one and of seven for the other three cations, provided by oxide and fluoride anions. The overall arrangement of the building blocks can be considered as layer-like parallel to the ac plane.

Studies of the K–Ba–Ga–Sn system produced the clathrate compounds K0.8(2)Ba15.2(2)Ga31.0(5)Sn105.0(5)[a= 17.0178 (4) Å], K4.3(3)Ba11.7(3)Ga27.4(4)Sn108.6(4)[a= 17.0709 (6) Å] and K12.9(2)Ba3.1(2)Ga19.5(4)Sn116.5(4)[a= 17.1946 (8) Å], with the type-II structure (cubic, space groupFd\overline{3}m), and K7.7(1)Ba0.3(1)Ga8.3(4)Sn37.7(4)[a= 11.9447 (4) Å], with the type-I structure (cubic, space groupPm\overline{3}n). For the type-II structures, only the smaller (Ga,Sn)24pentagonal dodecahedral cages are filled, while the (Ga,Sn)28hexakaidecahedral cages remain empty. The unit-cell volume is directly correlated with the K:Ba ratio, since an increasing amount of monovalent K occupying the cages causes a decreasing substitution of the smaller Ga in the framework. All three formulae have an electron count that is in good agreement with the Zintl–Klemm rules. For the type-I compound, all framework sites are occupied by a mixture of Ga and Sn atoms, with Ga showing a preference for Wyckoff site 6c. The (Ga,Sn)20pentagonal dodecahedral cages are occupied by statistically disordered K and Ba atoms, while the (Ga,Sn)24tetrakaidecahedral cages encapsulate only K atoms. Large anisotropic displacement parameters for K in the latter cages suggest an off-centering of the guest atoms.

This paper presents results from our exploratory work in the systems K-Cd-Ge, Rb-Cd-Ge, and Cs-Cd-Ge, which yielded the novel type-I clathrates with refined compositions K8Cd3.77(7)Ge42.23, Rb8Cd3.65(7)Ge42.35, and Cs7.80(1)Cd3.65(6)Ge42.35. The three compounds represent rare examples of clathrates of germanium with the alkali metals, where a d10 element substitutes a group 14 element. The three structures, established by single-crystal X-ray diffraction, indicate that the framework-building Ge atoms are randomly substituted by Cd atoms on only one of the three possible crystallographic sites. This and several other details of the crystal chemistry are elaborated.

Investigations of the system Ba–In–Sn, with the objective to synthesize Ba8In16Sn30 clathrate using Sn and In flux reactions, yielded instead the known BaSn3 compound (P63/mmc, a = 7.228(2) Å, c = 5.469(3) Å) from Sn flux and its In-doped variant BaSn2.8In0.2(1) (a = 7.260(1) Å, c = 5.382(2) Å) from In flux. BaSn3–xInx is the first, and up until now, the only ternary phase containing these elements. Its structure is isomorphic with the Ni3Sn type (Pearson symbol hP8) and is apparently capable of sustaining small variations in the valence electron count by virtue of replacing Sn with the electron poorer In. Electrical resistivity measurements on single-crystals of both undoped and doped phases show different metallic-like behavior, suggesting that neither BaSn3 nor BaSn3–xInx are valence compounds.

While searching for new and effective materials as host lattices for luminescence (Blasse and Grabmaier 1994; Dieke 1968; Hoppe 2009; Justel et al. 1998; Ronda 2008), synthetic oxosilicates containing rare-earth metal(III) cations and fluoride anions got into the focus of our work (Schleid et al. 2011). In some cases, the charge compensation is achieved using alkali metals such as sodium to cesium or alkaline-earth metals such as calcium to barium.

B3DyO6, orthorhombic, Pnma (no. 62), a = 15.9431(9) A, b = 7.4036(4) A, c = 12.2618(7) A, V = 1447.3 A, Z = 16, Rgt(F) = 0.026, wRref(F) = 0.053, T = 293 K. Source of material Single crystals of -Dy(BO2)3 have been obtained by the reaction of Dy2O3 and B2O3 in the stoichiometric ratio 1 : 3 with a slight excess of fluxing DyCl3 in gas tightly sealed platinum crucibles within three weeks at 900 °C. The compound appears as colourless, thin, airand water-resistant needles which tend to severe growth-twinning due to their fibrous habit. Discussion In the range of the lanthanidemeta-oxoboratesM(BO2)3 (M = La Lu) there are meanwhile four modifications known of which three are realized for the light representatives. The -type compounds could be obtained under normal-pressure hightemperature conditions for M = La Nd, Sm Tb and crystallize monoclinically with space group I2/a (C2/c), e.g. [1]. Two highpressure high-temperature modifications were recently synthesized: the orthorhombic -M(BO2)3-type (M = La – Nd, Pca21) [2] and the monoclinic -La(BO2)3-type compounds (P21/c) [3]. For the first time, an example of the fourth known phase ofmetaoxoborates, -Tb(BO2)3 was obtained under normal-pressure high-temperature conditions [4], whereas single crystals of M(BO2)3 with M = Dy Lu [5] were accessible under highpressure high-temperature conditions exclusively. Only the here presented compound can be additionally synthesized under normal pressure. In the crystal structure, vertex-linked [BO4] tetrahedra [d(B—O) = 143 – 153 pm] are connected to strongly corrugated oxoborate layers running parallel to (100). Between these layers the four crystallographically independent Dy cations are located, each surrounded by eight oxide anions [d(Dy—O) = 226 – 283 pm]. Z. Kristallogr. NCS 223 (2008) 177-178 / DOI 10.1524/ncrs.2008.0073 177 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: colourless needle, size 0.02 × 0.04 × 0.09 mm Wavelength: Mo K radiation (0.71069 A) : 205.78 cm−1 Diffractometer: Bruker-Nonius -CCD 2 max: 54.96° N(hkl)measured, N(hkl)unique: 18898, 1789 Criterion for Iobs, N(hkl)gt: Iobs > 2 (Iobs), 1680 N(param)refined: 197 Programs: SHELXS-97 [6], SHELXL-97 [7], DIAMOND [8] Table 1. Data collection and handling.