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We report magnetization measurements, full-potential band-structure calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets A2CuP2O7 (A = Na, Li) involving complex Cu-O-O-Cu superexchange pathways. Based on a quantitative evaluation of the leading exchange integrals and the subsequent quantum Monte Carlo simulations, we propose a quasi-one-dimensional magnetic model for both compounds, in contrast to earlier studies that conjectured on a two-dimensional scenario. The one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization isotherms measured in fields up to 50 T. The saturation fields of about 40 T for both Li and Na compounds are in excellent agreement with the intrachain exchange J1 ≃ 27 K extracted from the magnetic susceptibility data. The proposed magnetic structure entails spin chains with the dominating antiferromagnetic nearest-neighbor interaction J1 and two inequivalent, nonfrustrated antiferromagnetic interchain couplings of about 0.01J1 each. A possible long-range magnetic ordering is discussed in comparison with the available experimental information. [ABSTRACT FROM AUTHOR]

Unusual Ti–Cr–Zr-rich garnet crystals from high-temperature melilitic skarn of the Maronia area, western Thrace, Greece, were investigated by electron-microprobe analysis, powder and single-crystal X-ray diffraction, IR, Raman and Mössbauer spectroscopy. Chemical data showed that the garnets contain up to 8 wt.% TiO2, 8 wt.% Cr2O3 and 4 wt.% ZrO2, representing a solid solution of andradite (Ca3Fe3+ 2Si3O12 ≈46 mol%), uvarovite (Ca3Cr2Si3O12 ≈23 mol%), grossular (Ca3Al2Si3O12 ≈10 mol%), schorlomite (Ca3Ti2[Si,(Fe3+,Al3+)2]O12 ≈15 mol%), and kimzeyite (Ca3Zr2[Si,Al2]3O12 ≈6 mol%). The Mössbauer analysis showed that the total Fe is ferric, preferentially located at the octahedral site and to a smaller extent at the tetrahedral site. Single-crystal XRD analysis, Raman and IR spectroscopy verified substitution of Si mainly by Al3+, Fe3+ and Ti4+. Cr3+ and Zr4+ are found at the octahedral site along with Fe3+, Al3+ and Ti4+. The measured H2O content is 0.20 wt.%. The analytical data suggest that the structural formula of the Maronia garnet can be given as: (Ca2.99Mg0.03)Σ=3.02(Fe3+ 0.67Cr0.54Al0.33Ti0.29Zr0.15)Σ=1.98(Si2.42Ti0.24Fe0.18Al0.14)Σ=2.98O12OH0.11. Ti-rich garnets are not common and their crystal chemistry is still under investigation. The present work presents new evidence that will enable the elucidation of the structural chemistry of Ti- and Cr-rich garnets. [ABSTRACT FROM AUTHOR]

The crystal structure of the synthetic iron phosphate Na0.10(1)Fe6.99(1)(P1.00(1)O4)6 has been refined at 270 and 100 K from single-crystal X-ray diffraction data. The compound is triclinic, P−1, Z=1, lattice parameters: a=6.3944(9) Å, b=7.956(1) Å, c=9.364(1) Å, α=105.13(1)°, β=108.35(1)°, γ=101.64(1)° at 270 K and adopts the well-known howardevansite structure type. Iron, being both in the divalent and the trivalent valence state, is ordered on the four symmetry non-equivalent iron positions [Fe2+ on Fe(1) and Fe(3), Fe3+ on Fe(2) and Fe(4)]. Three of the four iron positions show octahedral oxygen atom coordination, the fourth one, which is occupied by Fe2+, is five-fold coordinated. The structure consists of crankshafts (buckled chains) of edge sharing Fe-oxygen polyhedra, passing through the unit cell in [101] direction. Structural investigation at 100 K shows no change of symmetry. The valence state and distribution of iron was determined by 57Fe Mössbauer spectroscopy. The compound shows 4 subspectra in agreement with the four different Fe sites. The assignment of the Fe2+ doublets to the Fe(1) and Fe(3) sites is trivial due to the 2:1 stoichiometry, also found in the Mössbauer spectra. For the Fe3+ sites, the temperature-dependent variation of structural distortion parameters and the quadrupole splitting led to a clear doublet assignment. [Copyright &y& Elsevier]

Stable ^{205}Tl ions have the lowest known energy threshold for capturing electron neutrinos (ν_{e}) of E_{ν_{e}}≥50.6  keV. The Lorandite Experiment (LOREX), proposed in the 1980s, aims at obtaining the longtime averaged solar neutrino flux by utilizing natural deposits of Tl-bearing lorandite ores. To determine the ν_{e} capture cross section, it is required to know the strength of the weak transition connecting the ground state of ^{205}Tl and the 2.3 keV first excited state in ^{205}Pb. The only way to experimentally address this transition is to measure the bound-state beta decay (β_{b}) of fully ionized ^{205}Tl^{81+} ions. After three decades of meticulous preparation, the half-life of the β_{b} decay of ^{205}Tl^{81+} has been measured to be 291_{-27}^{+33}  days using the Experimental Storage Ring (ESR) at GSI, Darmstadt. The longer measured half-life compared to theoretical estimates reduces the expected signal-to-noise ratio in the LOREX, thus challenging its feasibility.

The interface stability versus Li represents a major challenge in the development of next-generation all-solid-state batteries (ASSB), which take advantage of the inherently safe ceramic electrolytes. Cubic Li 7 La 3 Zr 2 O 12 garnets represent the most promising electrolytes for this technology. The high interfacial impedance versus Li is, however, still a bottleneck toward future devices. Herein, we studied the electrochemical performance of Fe 3+ -stabilized Li 7 La 3 Zr 2 O 12 (LLZO:Fe) versus Li metal and found a very high total conductivity of 1.1 mS cm -1 at room temperature but a very high area specific resistance of ∼1 kΩ cm 2 . After removing the Li metal electrode we observe a black surface coloration at the interface, which clearly indicates interfacial degradation. Raman- and nanosecond laser-induced breakdown spectroscopy reveals, thereafter, the formation of a 130 μm thick tetragonal LLZO interlayer and a significant Li deficiency of about 1-2 formula units toward the interface. This shows that cubic LLZO:Fe is not stable versus Li metal by forming a thick tetragonal LLZO interlayer causing high interfacial impedance., Competing Interests: The authors declare no competing financial interest.

Li oxide garnets are among the most promising candidates for solid-state electrolytes in novel Li ion and Li metal based battery concepts. Cubic Li 7 La 3 Zr 2 O 12 stabilized by a partial substitution of Zr 4+ by Bi 5+ has not been the focus of research yet, despite the fact that Bi 5+ would be a cost-effective alternative to other stabilizing cations such as Nb 5+ and Ta 5+ . In this study, Li 7-x La 3 Zr 2-x Bi x O 12 (x = 0.10, 0.20, ..., 1.00) was prepared by a low-temperature solid-state synthesis route. The samples have been characterized by a rich portfolio of techniques, including scanning electron microscopy, X-ray powder diffraction, neutron powder diffraction, Raman spectroscopy, and 7 Li NMR spectroscopy. Pure-phase cubic garnet samples were obtained for x ≥ 0.20. The introduction of Bi 5+ leads to an increase in the unit-cell parameters. Samples are sensitive to air, which causes the formation of LiOH and Li 2 CO 3 and the protonation of the garnet phase, leading to a further increase in the unit-cell parameters. The incorporation of Bi 5+ on the octahedral 16a site was confirmed by Raman spectroscopy. 7 Li NMR spectroscopy shows that fast Li ion dynamics are only observed for samples with high Bi 5+ contents.

Fast Li-ion-conducting Li oxide garnets receive a great deal of attention as they are suitable candidates for solid-state Li electrolytes. It was recently shown that Ga-stabilized Li 7 La 3 Zr 2 O 12 crystallizes in the acentric cubic space group I 4̅3 d . This structure can be derived by a symmetry reduction of the garnet-type Ia 3̅ d structure, which is the most commonly found space group of Li oxide garnets and garnets in general. In this study, single-crystal X-ray diffraction confirms the presence of space group I 4̅3 d also for Li 7-3 x Fe x La 3 Zr 2 O 12 . The crystal structure was characterized by X-ray powder diffraction, single-crystal X-ray diffraction, neutron powder diffraction, and Mößbauer spectroscopy. The crystal-chemical behavior of Fe 3+ in Li 7 La 3 Zr 2 O 12 is very similar to that of Ga 3+ . The symmetry reduction seems to be initiated by the ordering of Fe 3+ onto the tetrahedral Li1 (12 a ) site of space group I 4̅3 d . Electrochemical impedance spectroscopy measurements showed a Li-ion bulk conductivity of up to 1.38 × 10 -3 S cm -1 at room temperature, which is among the highest values reported for this group of materials.

Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li 7 La 3 Zr 2 O 12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet ( Ia 3̅ d , No. 230) to "non-garnet" ( I 4̅3 d , No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10 -4 S cm -1 to 1.2 × 10 -3 S cm -1 , which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm 2 , the lowest reported value for LLZO so far. These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

Li-oxide garnets such as Li 7 La 3 Zr 2 O 12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia -3 d , has to be stabilized with supervalent cations. LLZO stabilized with Ga 3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characterization of Ga-stabilized LLZO is performed by means of single-crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred micrometers are obtained by solid-state reaction. Single-crystal X-ray diffraction results show that Li 7-3 x Ga x La 3 Zr 2 O 12 with x > 0.07 crystallizes in the acentric cubic space group I -43 d . This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga 3+ . 7 Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I -43 d compared to space group Ia -3 d . Despite all efforts undertaken to reveal structure-property relationships for this class of materials, this study highlights the potential for new discoveries.

This paper focuses on constraining the erosion rate in the area of the Allchar Sb-As-Tl-Au deposit (Macedonia). It contains the largest known reserves of lorandite (TlAsS 2 ), which is essential for the LORanditeEXperiment (LOREX), aimed at determining the long-term solar neutrino flux. Because the erosion history of the Allchar area is crucial for the success of LOREX, we applied terrestrial in situ cosmogenic nuclides including both radioactive ( 26 Al and 36 Cl) and stable ( 3 He and 21 Ne) nuclides in quartz, dolomite/calcite, sanidine, and diopside. The obtained results suggest that there is accordance in the values obtained by applying 26 Al, 36 Cl, and 21 Ne for around 85% of the entire sample collection, with resulting erosion rates varying from several tens of m/Ma to ∼165 m/Ma. The samples from four locations (L-8 CD, L1b/R, L1c/R, and L-4/ADR) give erosion rates between 300 and 400 m/Ma. Although these localities reveal remarkably higher values, which may be explained by burial events that occurred in part of Allchar, the erosion rate estimates mostly in the range between 50 and 100 m/Ma. This range further enables us to estimate the vertical erosion rate values for the two main ore bodies Crven Dol and Centralni Deo. We also estimate that the lower and upper limits of average paleo-depths for the ore body Centralni Deo from 4.3 Ma to the present are 250-290 and 750-790 m, respectively, whereas the upper limit of paleo-depth for the ore body Crven Dol over the same geological age is 860 m. The estimated paleo-depth values allow estimating the relative contributions of 205 Pb derived from pp-neutrino and fast cosmic-ray muons, respectively, which is an important prerequisite for the LOREX experiment.

Cubic Li7La3Zr2O12 (LLZO) garnets are exceptionally well suited to be used as solid electrolytes or protecting layers in "Beyond Li-ion Battery" concepts. Unfortunately, cubic LLZO is not stable at room temperature (RT) and has to be stabilized by supervalent dopants. In this study we demonstrate a new possibility to stabilize the cubic phase at RT via substitution of Zr(4+) by Mo(6+). A Mo(6+) content of 0.25 per formula unit (pfu) stabilizes the cubic LLZO phase, and the solubility limit is about 0.3 Mo(6+) pfu. Based on the results of neutron powder diffraction and Raman spectroscopy, Mo(6+) is located at the octahedrally coordinated 16a site of the cubic garnet structure (space group Ia-3d). Since Mo(6+) has a smaller ionic radius compared to Zr(4+) the lattice parameter a0 decreases almost linearly as a function of the Mo(6+) content. The highest bulk Li-ion conductivity is found for the 0.25 pfu composition, with a typical RT value of 3.4 × 10(-4) S cm(-1). An additional significant resistive contribution originating from the sample interior (most probably from grain boundaries) could be identified in impedance spectra. The latter strongly depends on the prehistory and increases significantly after annealing at 700 °C in ambient air. Cyclic voltammetry experiments on cells containing Mo(6+) substituted LLZO indicate that the material is stable up to 6 V.

A series of Fe 3+ -bearing Li 7 La 3 Zr 2 O 12 (LLZO) garnets was synthesized using solid-state synthesis methods. The synthetic products were characterized compositionally using electron microprobe analysis and inductively coupled plasma optical emission spectroscopy (ICP-OES) and structurally using X-ray powder diffraction and 57 Fe Mössbauer spectroscopy. A maximum of about 0.25 Fe 3+ pfu could be incorporated in Li 7-3 x Fe x La 3 Zr 2 O 12 garnet solid solutions. At Fe 3+ concentrations lower than about 0.16 pfu, both tetragonal and cubic garnets were obtained in the synthesis experiments. X-ray powder diffraction analysis showed only a garnet phase for syntheses with starting materials having intended Fe 3+ contents lower than 0.52 Fe 3+ pfu. Back-scattered electron images made with an electron microprobe also showed no phase other than garnet for these compositions. The lattice parameter, a 0 , for all solid-solution garnets is similar with a value of a 0 ≈12.98 Å regardless of the amount of Fe 3+ . 57 Fe Mössbauer spectroscopic measurements indicate the presence of poorly- or nano-crystalline FeLaO 3 in syntheses with Fe 3+ contents greater than 0.16 Fe 3+ pfu. The composition of different phase pure Li 7-3 x Fe x La 3 Zr 2 O 12 garnets, as determined by electron microprobe (Fe, La, Zr) and ICP-OES (Li) measurements, give Li 6.89 Fe 0.03 La 3.05 Zr 2.01 O 12 , Li 6.66 Fe 0.06 La 3.06 Zr 2.01 O 12 , Li 6.54 Fe 0.12 La 3.01 Zr 1.98 O 12 , and Li 6.19 Fe 0.19 La 3.02 Zr 2.04 O 12 . The 57 Fe Mössbauer spectrum of cubic Li 6.54 Fe 0.12 La 3.01 Zr 1.98 O 12 garnet indicates that most Fe 3+ occurs at the special crystallographic 24 d position, which is the standard tetrahedrally coordinated site in garnet. Fe 3+ in smaller amounts occurs at a general 96 h site, which is only present for certain Li-oxide garnets, and in Li 6.54 Fe 0.12 La 3.01 Zr 1.98 O 12 this Fe 3+ has a distorted 4-fold coordination.

Fast-conducting phase-pure cubic Ga-bearing Li7La3Zr2O12 was obtained using solid-state synthesis methods with 0.08 to 0.52 Ga(3+) pfu in the garnet. An upper limit of 0.72 Ga(3+) pfu in garnet was obtained, but the synthesis was accompanied by small amounts of La2Zr2O12 and LiGaO3. The synthetic products were characterized by X-ray powder diffraction, electron microprobe and SEM analyses, ICP-OES measurements, and (71)Ga MAS NMR spectroscopy. The unit-cell parameter, a0, of the various garnets does not vary significantly as a function of Ga(3+) content, with a value of about 12.984(4) Å. Full chemical analyses for the solid solutions were obtained giving: Li7.08Ga0.06La2.93Zr2.02O12, Li6.50Ga0.15La2.96Zr2.05O12, Li6.48Ga0.23La2.93Zr2.04O12, Li5.93Ga0.36La2.94Zr2.01O12, Li5.38Ga0.53La2.96Zr1.99O12, Li4.82Ga0.60La2.96Zr2.00O12, and Li4.53Ga0.72La2.94Zr1.98O12. The NMR spectra are interpreted as indicating that Ga(3+) mainly occurs in a distorted 4-fold coordinated environment that probably corresponds to the general 96h crystallographic site of garnet.

We investigate theoretically the site occupancy of Al 3+ in the fast-ion-conducting cubic-garnet Li 7-3 x Al 3+ x La 3 Zr 2 O 12 ( Ia -3 d) using density functional theory. By comparing calculated and measured 27 Al NMR chemical shifts an analysis shows that Al 3+ prefers the tetrahedrally coordinated 24 d site and a distorted 4-fold coordinated 96 h site. The site energies for Al 3+ ions, which are slightly displaced from the exact crystallographic sites (i.e., 24 d and 96 h ), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad 27 Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al 3+ could also occupy the 48 g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al 3+ site has not been observed experimentally.

Nominal Li7La3Zr2O12 (LLZO) garnet, doped with (57)Fe2O3, was synthesized by sintering oxides and carbonates at T = 1100 °C in air. X-ray powder diffraction measurements show that Li(7-3x)Fe(3+)(x)La3Zr2O12 with x = 0.19 crystallizes in the cubic space group Ia-3d, with a0 = 12.986(4) Å at room temperature. SEM and electron microprobe measurements were made to obtain compositional information and check for the presence of phases other than garnet. Inductively coupled plasma optical emission spectroscopy measurements were made to determine the Li content. (57)Fe Mössbauer spectra obtained at 295 and 80 K show that about 96% of the total iron occurs as Fe(3+) and 4% as Fe(2+). Roughly two-thirds of the Fe(3+) cations are assigned to the tetrahedral site (24d) and roughly one-quarter to a highly distorted site (possibly at 96h) in the garnet structure. Smaller amounts of Fe(3+) and Fe(2+), around 5% each, occur at other crystallographic sites. On the basis of published (27)Al MAS NMR results and analysis of the (57)Fe Mössbauer spectra, it appears that at low concentrations Al(3+) and Fe(3+) substitute in Li7La3Zr2O12 in a similar manner. The aliovalent substitution Al(3+)/Fe(3+) ↔ 3Li(+) in LLZO stabilizes the cubic phase and also probably promotes its high Li-ion conductivity.

The structure analyses of sodium chromium digermanate, NaCrGe(2)O(6), (I), and lithium chromium digermanate, LiCrGe(2)O(6), (II), provide important structural information for the clinopyroxene family, and form part of our ongoing studies on the phase transitions and magnetic properties of clinopyroxenes. (I) shows C2/c symmetry at 298 K, contains one Na, one Cr (both site symmetry 2 on special position 4e), one Ge and three O-atom positions (on general positions 8f) and displays the well known clinopyroxene topology. The basic units of the structure of (I) are infinite zigzag chains of edge-sharing Cr(3+)O(6) octahedra (M1 site), infinite chains of corner-sharing GeO(4) tetrahedra, connected to the M1 chains by common corners, and Na sites occupying interstitial space. (II) was found to have P2(1)/c symmetry at 298 K. The structure contains one Na, one Cr, two distinct Ge and six O-atom positions, all on general positions 4e. The general topology of the structure of (II) is similar to that of (I); however, the loss of the twofold symmetry makes it possible for two distinct tetrahedral chains, having different conformation states, to exist. While sodium is (6+2)-fold coordinated, lithium displays a pure sixfold coordination. Structural details are given and chemical comparison is made between silicate and germanate chromium-based clinopyroxenes.

Germanate compounds, CaMGeO(4) with M(2+) = Ca, Mg, Co and Mn, were synthesized as single crystals by slow cooling from the melt or by flux growth techniques. All the compositions investigated exhibit Pnma symmetry at 298 K and adopt the olivine structure. The M2 site is exclusively occupied by Ca(2+), while on M1 both Ca(2+) and M(2+) cations are found. The amount of Ca(2+) on M1 increases with the size of the M1 cation, with the smallest amount in the Mg compound (0.1 atoms per formula unit) and the largest in the Mn compound (0.20 atoms per formula unit), while in Ca(2)GeO(4), also with olivine structure, both sites are completely filled with Ca(2+). When compared with those of Ca silicate olivine, the lattice parameters a and c are distinctly larger in the analogous germanate compounds, while b has essentially the same values, regardless of the tetrahedral cation, meaning that b is independent of the tetrahedral cation. Structural variations on the octahedrally coordinated M1 site are largely determined by the size of the M1 cation, the average M1-O bond lengths being identical in Ca silicate and Ca germanate olivine. Increasing the size of the M1 cation induces an increasing polyhedral distortion, expressed by the parameters bond-length distortion, octahedral angle variance and octahedral quadratic elongation. However, the Ca germanate olivine compounds generally have more regular octahedra than the analogous silicates. The octahedrally coordinated M2 site does not exhibit large variations in structural parameters as a consequence of the constant chemical composition; the same is valid for the tetrahedral site.

Disodium hexamanganese(II,III) germanate is the first aenigmatite-type compound with significant amounts of manganese. Na(2)(Mn(5.26)Na(0.74))Ge(6)O(20) is triclinic and contains two different Na positions, six Ge positions and 20 O positions (all with site symmetry 1 on general position 2i of space group P1). Five out of the seven M positions are also on general position 2i, while the remaining two have site symmetry 1 (Wyckoff positions 1f and 1c). The structure can be described in terms of two different layers, A and B, stacked along the [011] direction. Layer A contains pyroxene-like chains and isolated octahedra, while layer B is built up by slabs of edge-sharing octahedra connected to one another by bands of Na polyhedra. The GeO(4) tetrahedra show slight polyhedral distortion and are among the most regular found so far in germanate compounds. The M sites of layer A are occupied by highly charged (trivalent) cations, while in layer B a central pyroxene-like zigzag chain can be identified, which contains divalent (or low-charged) cations. This applies to the aenigmatite-type compounds in general and to the title compound in particular.

The structure of diyttrium digermanate, Y(2)Ge(2)O(7), has been determined in the tetragonal space group P4(3)2(1)2. It contains one Y, one Ge (both site symmetry 1 on general position 8b) and four O atoms [one on special position 4a (site symmetry ..2) and the remaining three on general positions 8b]. The basic units of the structure are isolated Ge(2)O(7) groups, sharing one common O atom and displaying a Ge-O-Ge angle of 134.9 (3) degrees , and infinite helical chains of pentagonal YO(7) dipyramids, parallel to the 4(3) screw axis. The crystal investigated here represents the left-handed form of the tetragonal R(2)Ge(2)O(7) compounds (R = Eu(3+), Tb(3+), Er(3+), Tm(3+) and Lu(3+)).

The title compound, tricalcium monogermanate dichloride, is orthorhombic and consists of one distinct Ge site on special position 4c, site symmetry m, and two different Ca sites, Ca1 and Ca2, one on general position 8d, site symmetry 1, and the other on special position 4c. Two of the O atoms occupy the 4c position (symmetry m); the third O atom is situated on the general 8d position, symmetry 1, as is the one distinct Cl position. By sharing common edges, the distorted Ca1 octahedra form infinite crankshaft-like chains parallel to the b direction. Along a and c, these chains are connected to one another via common corners, thereby forming a three-dimensional framework of edge- and corner-sharing Ca1O(4)Cl(2) octahedra. Triangular prisms of Ca2O(4)Cl(2) polyhedra and GeO(4) tetrahedra fill the interstitial space within the Ca1 polyhedral framework. Relationships between the structures of the title compound and the humite-type materials norbergite (Mg(3)SiO(4)F(2)) and Mn(3)SiO(4)F(2) are discussed.

The structure of dicalcium heptagermanate, previously described with an orthorhombic space group, has been redetermined in the tetragonal space group P(overline4)b2. It contains three Ge positions (site symmetry 1, ..2 and 2.22, respectively), one Ca position (..2) and four O atoms, all on general 8i positions (site symmetry 1). A sheet of four-membered rings of Ge tetrahedra (with Ge on the 8i position) and isolated Ge tetrahedra (Ge on the 4g position) alternate with a sheet of Ge octahedra (Ge on the 2d position) and eightfold-coordinated Ca sites along the c direction in an ABABA... sequence. The three-dimensional framework of Ge sites displays a channel-like structure, evident in a projection on to the ab plane.

The structure of copper(I,II) pentachromium(III) germanate, Cu(Cu(0.44)Cr(4.56))Ge(2)O(12), contains one Cu position (m2m), one Ge position (m) and three Cr positions (2/m, m and 2). The close-packed structure is described in terms of slabs of edge-sharing Cr(3+)O(6) octahedra and isolated CuO(4) and GeO(4) tetrahedra. These slabs are aligned parallel to the bc plane and are separated from each other by GeO(4) tetrahedra along a. The tetrahedral coordination observed for the Cu(+)/Cu(2+) ions represents an unusual feature of the structure. The Cr-O and Cu-O bond lengths are compared with literature data.

The germanate compound Cu2Fe2Ge4O13, dicopper diiron germanate, was synthesized by solid-state reaction at 1403 K and ambient pressure. There is no change of space-group symmetry between 10 and 900 K. Between 40 K and room temperature the a lattice parameter shows a negative thermal expansion which can be connected to a decreasing Cu-Cu interatomic distance. Above room temperature all the lattice parameters are positively correlated with temperature. Among the structural parameters several alterations with temperature occur, which are most prominent for the distorted Fe3+ octahedral site. Besides an increase of the average bond length and of the interatomic Fe-Fe distances, distortional parameters also increase with temperature, while the average Cu-O bond length remains almost constant between 100 and 900 K, as do the average Ge-O distances. 57Fe Mössbauer spectroscopy was used to detect long-range magnetic ordering in Cu2Fe2Ge4O13. While around 100 K, which is the temperature at which a broad maximum is observed in the magnetic susceptibility, no magnetic ordering was detected in the Mössbauer spectrum, below 40 K a narrow split sextet is developed which is indicative of a three-dimensional magnetic ordering of the sample.

The title compound, octacalcium copper pentagermanium octadecaoxide, represents a new intermediate phase between CaO and GeO2, and has not previously been reported in the literature. The structure consists of three different Ge sites, two of them on general 8d positions, site symmetry 1, one on special position 4d, site symmetry 2. Three of the five Ca sites occur on 8d positions, site symmtery 1, one Ca is on 4b with site symmetry -1 and one Ca is on 4c with site symmetry 2. All nine O atoms have symmetry 1 (8d position). By sharing common edges, the Ca sites form infinite bands parallel to the c axis, and these bands are interconnected by isolated GeO4 and Ge3O10 units. These (100) layers are stacked along a in an ABAB... sequence, with the B layer being inverted and displaced along b/2.

Mössbauer measurements at different temperatures are reported for MWCNTs with metallic encapsulations ("nanowires"). The spectra can reasonably be refined with two subpatterns: one providing clear evidence of an iron carbide Fe(3)C (cementite) phase as the main nanowire component and the other yielding a relaxation doublet most probably belonging to the same phase. Whereas the former one displays a well resolved magnetic hyperfine spectrum with Brillouin type temperature dependence, the latter one gains importance with rising temperature or onset of an inhomogeneous external magnetic field. The comparably large incoherent scattering is attributed to the graphene layers of the tube walls. The experimental results are discussed on the background of an interpretation model trying to explain unusual magnetometric results published elsewhere.

The structure of the basic iron phosphate rockbridgeite [iron manganese zinc tris(phosphate) pentahydroxide] was reinvestigated with special emphasis on the cation distribution deduced from new X-ray and 57Fe Mössbauer data. Rockbridgeite is orthorhombic, space group Cmcm, and shows three different Fe sites, one with 2/m symmetry, another with m symmetry and the third in a general position. One phosphate group has the P atom on a site with m symmetry, while the other has the P atom at a site with mm symmetry. Two Fe sites are fully occupied by ferric iron, while Mn3+ and Fe2+ are situated at a third, principally Fe, site. Structural data, bond-valence sums and polyhedral distortion parameters suggest a new interpretation of the rockbridgeite 57Fe Mössbauer spectrum.

CaCuGe2O6 shows a strongly distorted clinopyroxene-type structure with P2(1)/c symmetry at 298 K. The Cu2+ ion at the M1 site is coordinated by six O atoms forming an octahedron, which deviates significantly from ideal geometry. Individual M1 sites are connected via common edges to form an infinite zigzag chain parallel to the crystallographic c axis. The Ca2+ ion at M2 shows a sevenfold coordination. M2 sites are connected to the M1 chain via three common edges, thereby forming a metal layer within the bc plane. Besides the strong Jahn-Teller distortion of the Cu site, the structure of the title compound differs from ;normal' clinopyroxenes by a distortion of alternate layers of Ge sites. While the Ge(A) site is fourfold coordinated by O atoms, forming infinite chains of corner-sharing chains parallel to the c axis, the Ge(B) site exhibits a fivefold coordination, thereby forming a true two-dimensional layer of edge-sharing GeO5 bipyramids. Decreasing the temperature causes a magnetic phase transition at 40 K, as monitored by a broad maximum in the magnetic susceptibility and by discontinuities in the lattice parameters. Increasing the temperature causes variations in bond lengths, edge lengths and bond angles. Most prominent is the increase of one bond length of the Ge(B) site and the increase of the tetrahedral bridging angle of the Ge(A) site. At 660 K a crystallographic phase transition is observed where the symmetry changes from P2(1)/c to C2/c. The transition is accompanied by large changes in the lattice parameters which are indicative of distinct topological changes of several structural building units. The high-temperature C2/c structure is similar to that of the germanate clinopyroxene CaMgGe2O6.