[en] Nanocrystalline Gd₂O₂NCN (P anti 3m1, crystallite size 30-40 nm) was synthesized upon ammonolysis of bis[[(N-carboxymethyl,N-carboxy-κO-methyl)amino-κN-ethyl]-glycinato( 3-)-κN,κO]gadolinium(III) (diethylenetriamine pentaacetic acid gadolinium(III) dihydrogen salt or gadopentetic acid, Gd-H₂DTPA hereafter) at 900 C. The conversion of Gd-H₂DTPA into Gd₂O₂NCN takes place in several steps, probably via transient formation of iminodiacetate-, glycinate-, and carbamate-containing complexes of Gd. Thermal treatment in air of Gd-H₂DTPA at 750 and 1300 C delivers nanocrystalline bixbyite-type Gd₂O₃ (Ia anti 3, crystallite size 30-70 nm); in an argon or nitrogen atmosphere the formation of monoclinic Gd₂O₃ (C2/m) was observed at 1300 C. The synthesized Gd₂O₂NCN converts upon thermal treatment in air, nitrogen, or argon atmosphere into monoclinic Gd₂O₃ (C2/m). In ammonia atmosphere, Gd₂O₂NCN seems to be stable against decomposition, even upon prolonged exposure to 1000 C. This study indicates that Gd-H₂DTPA may be a robust, low-cost, and flexible precursor for nanoscaled Gd-based nanopowders. Moreover, precursor approaches based on metal complexes using H₅DTPA as a ligand are suggested as promising access pathways towards nanocrystalline materials in the M/O/C/N system. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] The high-pressure behavior of KIO₃ was studied up to 30 GPa using single crystal and powder x-ray diffraction, Raman spectroscopy, second harmonic generation (SHG) experiments and density functional theory (DFT)-based calculations. Triclinic KIO₃ shows two pressure-induced structural phase transitions at 7 GPa and at 14 GPa. Single crystal x-ray diffraction at 8.7(1) GPa was employed to solve the structure of the first high-pressure phase (space group R3, a = 5.89(1) Å, α = 62.4(1)°). The bulk modulus, B, of this phase was obtained by fitting a second order Birch-Murnaghan equation of state (eos) to synchrotron x-ray powder diffraction data resulting in B_exp,second = 67(3) GPa. The DFT model gave B_DFT,second = 70.9 GPa, and, for a third order Birch-Murnaghan eos, B_DFT,third = 67.9 GPa with a pressure derivative of B_DFT,third^'=5.9. Both high-pressure transformations were detectable by Raman spectroscopy and the observation of second harmonic signals. The presence of strong SHG signals shows that all high-pressure phases are acentric. By using different pressure media, we showed that the transition pressures are very strongly influenced by shear stresses. Earlier work on low- and high-temperature transitions was complemented by low-temperature heat capacity measurements. We found no evidence for the presence of an orientational glass, in contrast to earlier dielectric studies, but consistent with earlier low-temperature diffraction studies. (paper)

[en] We report on a systematic study of the magnetic properties on single crystals of the solid solution Cs₂CuCl_4-xBr_x (0 ≤ x ≤ 4), which include the two known end-member compounds Cs₂CuCl₄ and Cs₂CuBr₄, classified as quasi-two-dimensional quantum antiferromagnets with different degrees of magnetic frustration. By comparative measurements of the magnetic susceptibility χ(T) on as many as eighteen different Br concentrations, we found that the in-plane and out-of-plane magnetic correlations do not show a smooth variation with x. Rather three distinct concentration regimes can be identified, which are separated by critical concentrations x_c1 = 1 and x_c1 = 2. This unusual magnetic behavior can be explained by considering the structural peculiarities of the materials, especially the distorted Cu-halide tetrahedra, which support a site-selective replacement of Cl^- by Br^- ions.

[en] Powder X-ray diffraction experiments of sillenites Bi₁₂M O₂₀ (M=Si, Ge, Ti) were performed with synchrotron radiation at the ESRF, Grenoble, at pressures up to 39 GPa (M=Si), 50 GPa (M=Ge), and 37 GPa (M=Ti), respectively. These three sillenites were investigated for the first time over such a large pressure range and they show no phase transition up to the highest pressures achieved. Birch–Murnaghan equations of state of third order were fitted to the pressure dependence of the lattice parameters. The resulting bulk moduli B₀ and their pressure derivatives B′ are B₀=63(1)GPa with B′=6.6(3) (M=Si), B₀=63.0(5)GPa with B′=5.90(7) (M=Ge), and B₀=48(1)GPa with B′=9.4(5) (M=Ti). In the case of Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀ the equation of state fits were restricted to pressures below 15 GPa, because the experimental data were affected by non-hydrostatic stress at higher pressures. The equation of state of neon was redetermined (V₀=11.7(6)cm³/mol, B₀=5(1)GPa, B′=5.5(3)GPa) and its use as an internal pressure standard for diffraction experiments is discussed. A second cubic phase could be identified in our Bi₁₂TiO₂₀ sample. This was attributed to eulytite-type Bi₄Ti₃O₁₂, which has B₀=50.9(8)GPa and B′=6.9(3). - Graphical abstract: X-ray diffraction at high pressure → Equation of state. - Highlights: • Powder X-ray diffraction experiments of sillenites were performed at high pressures. • Equations of state of sillenites Bi₁₂MO₂₀ (M=Si, Ge, Ti) were determined. • The sillenite structure was shown to be stable at high hydrostatic pressure. • Sillenites are sensitive to non-hydrostatic pressure conditions in neon-loaded DACs. • An eulytite-type Bi₄Ti₃O₁₂ phase was found to exist up to 10 GPa

[en] The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi₂Ga₄O₉, was determined up to 30.5 (5) GPa from in situ single-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3 (2), 6.2 (3), 8.9 (1) and 14.9 (3) GPa for the low-pressure phase, and at 21.4 (5) and 30.5 (5) GPa for the high-pressure phase. The mode-Grueneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50 GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The densityfunctional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50 GPa in accordance with the crystal structure of the high-pressure phase. While the stereochemical activity of the lone electron pair of Bi³⁺ is reduced at increasing pressure, a symmetrization of the bismuth coordination was not observed in this pressure range. This shows an unexpected stability of the localization of the lone electron pair and of its stereochemical activity at high pressure. (orig.)

[en] We present structural and magnetic data of a new Cu²⁺(S = 1/2)-containing magnetic trimer system 2b·3CuCl₂·2H₂O (b = betaine, C₅H₁₁NO₂). The trimers form a quasi-2D quantum spin system with an unusual intra-layer exchange coupling topology, which, in principle, supports diagonal four-spin exchange. To describe the magnetic properties, a 2D effective interacting-trimer model has been developed including an intra-trimer coupling J and two inter-trimer couplings J_a and J_b. The low-energy description and effective parameters are obtained from numerical calculations based on four coupled trimers (with periodic boundary conditions). Fits to the experimental data using this model yield the magnetic coupling constants J/k_B = -15 K and J_a/k_B = J_b/k_B = -4 K. These parameters describe the susceptibility and magnetization data very well over the whole temperature and field range investigated. Moreover, the model calculations indicate that, for certain ranges of the ratio J_b/J_a, which might be accessible by either chemical substitution and/or hydrostatic pressure, the low-energy properties of 2b·3CuCl₂·2H₂O will be dominated by non-trivial four-spin exchange processes.

[en] Large single crystals of orthorhombic [(CH₃)₃NCH₂COO]₂(CuCl₂)₃·2H₂O with dimensions up to 40×40×30 mm³ were grown from aqueous solutions. The elastic and piezoelastic coefficients were derived from ultrasonic resonance frequencies and their shifts upon variation of pressure, respectively, using the plate-resonance technique. Additionally, the coefficients of thermal expansion were determined between 95 K and 305 K by dilatometry. The elastic behaviour at ambient conditions is dominated by the 2-dimensional network of strong hydrogen bonds within the (001) plane leading to a corresponding pseudo-tetragonal anisotropy of the longitudinal elastic stiffness. The variation of elastic properties with pressure, however, as well as the thermal expansion shows strong deviations from the pseudo-tetragonal symmetry. These deviations are probably correlated with tilts of the elongated tri-nuclear betaine–CuCl₂–water complexes. Neither the thermal expansion nor the specific heat capacity gives any hint on a phase transition in the investigated temperature range. - Graphical abstract: Single crystal of orthorhombic [(CH₃)₃NCH₂COO]₂(CuCl₂)₃·2H₂O. - Highlights: • Large single crystals (40 ×40 ×30 mm³) of [(CH₃)₃NCH₂COO]₂(CuCl₂)₃·2H₂O were grown. • The elastic and piezoelastic coefficients were derived from ultrasonic resonance frequencies. • Thermal expansion (95 K–305 K) and heat capacity (113 K–323 K) were determined. • The orthorhombic structure shows pseudo-tetragonal elastic anisotropy at ambient conditions. • The crystal structure is stable in the investigated range (1–1600 bar, 95–303 K)

[en] The high-pressure behaviour of Bi₂Fe₄O₉ was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi₂Ga₄O₉. The lower phase transition pressure of Bi₂Fe₄O₉ with respect to that of Bi₂Ga₄O₉ (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga³⁺ and Fe³⁺ in tetrahedral coordination at high pressure. A fit of a second-order Birch-Murnaghan equation of state to the p-V data results in K₀ = 74(3) GPa for the low-pressure phase and K₀ = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements. (paper)

[en] A new oxalato-bridged copper(II) compound, Cu(ox)(pyOH)·H₂O (ox = oxalate, pyOH = 3-hydroxypyridine), has been synthesized and characterized by x-ray diffraction and magnetic susceptibility measurements. The Cu(II) ions are bridged by oxalate molecules with two different arrangements alternating along a chain parallel to the b-axis. To the best of our knowledge, this is the first example of a metal-oxalate chain with such a combination of oxalate bridges. Due to the specific structural properties, the magnetic susceptibility was analysed in the framework of an alternating-exchange spin-chain. From a least-squares fit, an antiferromagnetic coupling constant J₁ = (442 ± 5) K and an alternation parameter α = 0.13 ± 0.06 were derived, which classify Cu(ox)(pyOH)·H₂O as a strongly dimerized spin-chain compound. It is argued that the strength of the magnetic coupling is mainly determined by the displacement of the Cu(II) ions out of the basal plane of the local Cu environment

[en] The crystal structure of the bismuth silicon oxide Bi₁₂SiO₂₀ was determined by single-crystal x-ray diffraction at ambient conditions and at high pressure. Single-crystal intensity data between 0.0001 and 16.8(3) GPa were collected in house with Mo Kα radiation and with synchrotron radiation (λ = 0.45 A) at HASYLAB (D3), while lattice parameters were measured up to 23.0(3) GPa. The large cavities which exist in the crystal structure and host the lone electron pairs of the Bi³⁺ ions are considerably compressed at high pressure. The crystal structure, however, remains stable and the lone electron pair is stereochemically active up to at least 16.8 GPa. A larger compression in the direction of the lone electron pairs by shear deformation was not observed. Raman spectra of Bi₁₂SiO₂₀ were measured on powder samples during pressure decrease from 39.1(1) GPa down to ambient pressure and on single crystals during pressure increase up to 12.50(3) GPa. Density functional perturbation theory was used to compute Raman frequencies and intensities at ambient pressure and to investigate pressure-induced changes up to 50 GPa.