Nonmagnetic J=0 State and Spin-Orbit Excitations in K_{2}RuCl_{6}.

Spin-orbit Mott insulators composed of t_{2g}^{4} transition metal ions may host excitonic magnetism due to the condensation of spin-orbital J=1 triplons. Prior experiments suggest that the 4d antiferromagnet Ca_{2}RuO_{4} embodies this notion, but a J=0 nonmagnetic state as a basis of the excitonic picture remains to be confirmed. We use Ru L_{3}-edge resonant inelastic x-ray scattering to reveal archetypal J multiplets with a J=0 ground state in the cubic compound K_{2}RuCl_{6}, which are well described within the LS-coupling scheme. This result highlights the critical role of unquenched orbital moments in 4d-electron compounds and calls for investigations of quantum criticality and excitonic magnetism on various crystal lattices.

A spin-orbital-entangled quantum liquid on a honeycomb lattice.

The honeycomb lattice is one of the simplest lattice structures. Electrons and spins on this simple lattice, however, often form exotic phases with non-trivial excitations. Massless Dirac fermions can emerge out of itinerant electrons, as demonstrated experimentally in graphene, and a topological quantum spin liquid with exotic quasiparticles can be realized in spin-1/2 magnets, as proposed theoretically in the Kitaev model. The quantum spin liquid is a long-sought exotic state of matter, in which interacting spins remain quantum-disordered without spontaneous symmetry breaking. The Kitaev model describes one example of a quantum spin liquid, and can be solved exactly by introducing two types of Majorana fermion. Realizing a Kitaev model in the laboratory, however, remains a challenge in materials science. Mott insulators with a honeycomb lattice of spin-orbital-entangled pseudospin-1/2 moments have been proposed, including the 5d-electron systems α-Na2IrO3 (ref. 5) and α-Li2IrO3 (ref. 6) and the 4d-electron system α-RuCl3 (ref. 7). However, these candidates were found to magnetically order rather than form a liquid at sufficiently low temperatures, owing to non-Kitaev interactions. Here we report a quantum-liquid state of pseudospin-1/2 moments in the 5d-electron honeycomb compound H3LiIr2O6. This iridate does not display magnetic ordering down to 0.05 kelvin, despite an interaction energy of about 100 kelvin. We observe signatures of low-energy fermionic excitations that originate from a small number of spin defects in the nuclear-magnetic-resonance relaxation and the specific heat. We therefore conclude that H3LiIr2O6 is a quantum spin liquid. This result opens the door to finding exotic quasiparticles in a strongly spin-orbit-coupled 5d-electron transition-metal oxide.

Persistent Paramagnons Deep in the Metallic Phase of Sr_{2-x}La_{x}IrO_{4}.

We have studied the magnetic excitations of electron-doped Sr_{2-x}La_{x}IrO_{4} (0≤x≤0.10) using resonant inelastic x-ray scattering at the Ir L_{3} edge. The long-range magnetic order is rapidly lost with increasing x, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1/2 Heisenberg model with exchange interactions whose spatial range increases with doping. We also find a doping-independent high-energy magnetic continuum, which is not described by this model. The spin-orbit excitons arising from the pseudospin-3/2 manifold of the Ir ions broaden substantially in the SRO phase, but remain largely separated from the low-energy magnons. Pseudospin-1/2 models are therefore a good starting point for the theoretical description of the low-energy magnetic dynamics of doped iridates.

Hyperhoneycomb Iridate ß-Li2IrO3 as a platform for Kitaev magnetism.

A complex iridium oxide ß-Li(2)IrO(3) crystallizes in a hyperhoneycomb structure, a three-dimensional analogue of honeycomb lattice, and is found to be a spin-orbital Mott insulator with J(eff)=1/2 moment. Ir ions are connected to the three neighboring Ir ions via Ir-O(2)-Ir bonding planes, which very likely gives rise to bond-dependent ferromagnetic interactions between the J(eff)=1/2 moments, an essential ingredient of Kitaev model with a spin liquid ground state. Dominant ferromagnetic interaction between J(eff)=1/2 moments is indeed confirmed by the temperature dependence of magnetic susceptibility χ(T) which shows a positive Curie-Weiss temperature θ(CW)∼+40 K. A magnetic ordering with a very small entropy change, likely associated with a noncollinear arrangement of J(eff)=1/2 moments, is observed at T(c)=38 K. With the application of magnetic field to the ordered state, a large moment of more than 0.35 µ(B)/Ir is induced above 3 T, a substantially polarized J(eff)=1/2 state. We argue that the close proximity to ferromagnetism and the presence of large fluctuations evidence that the ground state of hyperhoneycomb ß-Li(2)IrO(3) is located in close proximity of a Kitaev spin liquid.

Understanding the adsorption mechanism of noble gases Kr and Xe in CPO-27-Ni, CPO-27-Mg, and ZIF-8.

An experimental study of Xe and Kr adsorption in metal-organic frameworks CPO-27-Ni, CPO-27-Mg, and ZIF-8 was carried out. In situ synchrotron X-ray powder diffraction experiments allowed precise determination of the adsorption sites and sequence of their filling with increasing of gas pressure at different temperatures. Structural investigations were used for interpretation of gas adsorption measurements.

A natural topological insulator.

The earth's crust and outer space are rich sources of technologically relevant materials which have found application in a wide range of fields. Well-established examples are diamond, one of the hardest known materials, or graphite as a suitable precursor of graphene. The ongoing drive to discover novel materials useful for (opto)electronic applications has recently drawn strong attention to topological insulators. Here, we report that Kawazulite, a mineral with the approximate composition Bi2(Te,Se)2(Se,S), represents a naturally occurring topological insulator whose electronic properties compete well with those of its synthetic counterparts. Kawazulite flakes with a thickness of a few tens of nanometers were prepared by mechanical exfoliation. They exhibit a low intrinsic bulk doping level and correspondingly a sizable mobility of surface state carriers of more than 1000 cm(2)/(V s) at low temperature. Based on these findings, further minerals which due to their minimized defect densities display even better electronic characteristics may be identified in the future.

Electronic phase separation in the slightly underdoped iron pnictide superconductor Ba1-xKxFe2As2.

Here we present a combined study of the slightly underdoped novel pnictide superconductor Ba1-xKxFe2As2 by means of x-ray powder diffraction, neutron scattering, muon-spin rotation (microSR), and magnetic force microscopy (MFM). Static antiferromagnetic order sets in below T{m} approximately 70 K as inferred from the neutron scattering and zero-field-microSR data. Transverse-field microSR below Tc shows a coexistence of magnetically ordered and nonmagnetic states, which is also confirmed by MFM imaging. We explain such coexistence by electronic phase separation into antiferromagnetic and superconducting- or normal-state regions on a lateral scale of several tens of nanometers. Our findings indicate that such mesoscopic phase separation can be considered an intrinsic property of some iron pnictide superconductors.

High-pressure crystal structure of the non-linear optical compound BiB(3)O(6) from two-dimensional powder diffraction data.

Our recently proposed method for automatic detection, calibration and evaluation of Debye-Scherrer ellipses using pattern-recognition techniques and advanced signal filtering was applied to the two-dimensional powder diffraction data of the non-ferroelectric, non-centrosymmetric non-linear optical (NLO) compound alpha-BiB(3)O(6) as a function of pressure. At ambient conditions, alpha-BiB(3)O(6) crystallizes in the space group C2 (phase I). In the pressure range between P = 6.09 and 6.86 GPa, it exhibits a first-order phase transition into a structure with the space group C1 (P1) [phase II at P = 8.34 GPa: a = 7.4781 (6), b = 3.9340 (4), c = 6.2321 (6) A, alpha = 93.73 (1), beta = 102.93 (1), gamma = 90.76 (1) degrees , and V = 178.24 (3) A(3)]. Non-linear compression behaviour over the entire pressure range is observed, which can be described by two Vinet relations in the ranges from P = 0.0 to 6.09 GPa, and from P = 6.86 to 11.6 GPa. The extrapolated bulk moduli of the high-pressure phases were determined to be K(0) = 38 (1) GPa for phase I, and K(0) = 114 (10) GPa for phase II. The crystal structures of both phases were refined against X-ray powder diffraction data measured at several pressures between 0.0 and 11.6 GPa. The structural phase transition of alpha-BiB(3)O(6) is mainly characterized by a reorientation of the [BO(3)](3-) triangles, the [BO(4)](5-) tetrahedra and the lone electron pair which is localized at Bi(3+), in order to optimize crystal packing.

Advances in data reduction of high-pressure x-ray powder diffraction data from two-dimensional detectors: a case study of schafarzikite (FeSb(2)O(4)).

Methods have been developed to facilitate the data analysis of multiple two-dimensional powder diffraction images. These include, among others, automatic detection and calibration of Debye-Scherrer ellipses using pattern recognition techniques, and signal filtering employing established statistical procedures like fractile statistics.All algorithms are implemented in the freely available program package Powder3D developed for the evaluation and graphical presentation of large powder diffraction data sets.As a case study, we report the pressure dependence of the crystal structure of iron antimony oxide FeSb(2)O(4) (p≤21 GPa, T = 298 K) using high-resolution angle dispersive x-ray powder diffraction. FeSb(2)O(4) shows two phase transitions in the measured pressure range. The crystal structures of all modifications consist of frameworks of Fe(2+)O(6) octahedra and irregular Sb(3+)O(4) polyhedra. At ambient conditions, FeSb(2)O(4) crystallizes in space group P4(2)/mbc (phase I). Between p = 3.2 GPa and 4.1 GPa it exhibits a displacive second order phase transition to a structure of space group P 2(1)/c (phase II, a = 5.7792(4) Å, b = 8.3134(9) Å, c = 8.4545(11) Å, ß = 91.879(10)°, at p = 4.2 GPa). A second phase transition occurs between p = 6.4 GPa and 7.4 GPa to a structure of space group P4(2)/m (phase III, a = 7.8498(4) Å, c = 5.7452(5) Å, at p = 10.5 GPa). A nonlinear compression behaviour over the entire pressure range is observed, which can be described by three Vinet equations in the ranges from p = 0.52 GPa to p = 3.12 GPa, p = 4.2 GPa to p = 6.3 GPa and from p = 7.5 GPa to p = 19.8 GPa. The extrapolated bulk moduli of the high-pressure phases were determined to K(0) = 49(2) GPa for phase I, K(0) = 27(3) GPa for phase II and K(0) = 45(2) GPa for phase III. The crystal structures of all phases are refined against x-ray powder data measured at several pressures between p = 0.52 GPa, and 10.5 GPa.

Effect of crystal packing on the structures of polymeric metallocenes.

The pressure dependencies of the crystal structures of the polymeric metallocenes lithium cyclopentadienide (LiCp) and potassium cyclopentadienide (KCp) have been determined by synchrotron X-ray powder diffraction. The decrease of the volume of LiCp by 34% up to a pressure of p = 12.2 GPa and of KCp by 23% at p = 5.3 GPa as well as the bulk moduli of K = 7.7 GPa for LiCp and 4.9 GPa for KCp indicate a high compressibility for these compounds. The crystal structures of KCp have been determined up to p = 3.9 GPa. An increase of the bend angle is found from 45 degrees at p = 0 GPa up to 51 degrees at p = 3.9 GPa. This variation is completely explained by a model invoking attractive K+ Cp- interaction and repulsive nonbonded carbon-carbon interactions. It is proposed that the bend angle in the polymeric alkali metal metallocenes is the result of the optimization of the crystal packing.

Decomposition of silver carbonate; the crystal structure of two high-temperature modifications of Ag(2)CO(3).

High-resolution powder diffraction was used to study the thermal transformation of silver carbonate. A sample of Ag(2)CO(3) was heated in a capillary under 4.5 atm CO(2) pressure. The decomposition temperature of silver carbonate to silver oxide is thereby increased, allowing high-resolution synchrotron X-ray powder diffraction patterns of the two high-temperature phases of Ag(2)CO(3) to be collected. The structure of the low-temperature (lt) phase was confirmed, and the structures of the two high-temperature phases were determined by direct methods and refined using the Rietveld method: lt-Ag(2)CO(3) (295 K) P2(1)/m, z = 2, a = 4.8521(2) A, b = 9.5489(4) A, c = 3.2536(1) A, beta = 91.9713(3) degrees; beta-Ag(2)CO(3) (453 K) P31c, z = 6, a = 9.1716(4) A, c = 6.5176(3) A; alpha-Ag(2)CO(3) (476 K) P6 macro 2m, z = 3, a = 9.0924(4) A, c = 3.3249(1) A. In addition, thermal expansion properties, anisotropic microstrain distributions, and thermal transformations of the three silver carbonate phases and silver oxide are described.

Bulk modulus and non-uniform compression of Nb3Te4 and InxNb3Te4 (x < 1) channel compounds.

The crystal structures of Nb3Te4 and InxNb3Te4 [x = 0.539 (4)] are reported for a series of pressures between 0 and 40 GPa. Both compounds crystallize in space group P6(3)/m with a = b = 10.671 and c = 3.6468 A for Nb3Te4, and a = b = 10.677 and c = 3.6566 A for InxNb3Te4 at ambient conditions. Phase transitions were not observed. High-pressure X-ray powder diffraction was measured using a diamond anvil cell and synchrotron radiation. Full Rietveld refinements provided the values of the lattice parameters and the values of the atomic coordinates at each pressure. The bulk modulus is found as K(0) = 70 (5) GPa for Nb3Te4 and as K(0) = 73 (4) GPa for InxNb3Te4. The analysis of the pressure dependences of the detailed crystal structures shows that the compression along c involves the folding up of the quasi-one-dimensional zigzag chains of Nb. The compression perpendicular to c is entirely due to the reduction of the diameter of the channels. The presence of intercalated In atoms is found to have hardly any influence on the compression behaviour up to 40 GPa.

Disordered crystal structure of pentamethylcyclopentadienylsodium as seen by high-resolution X-ray powder diffraction.

The crystal structure of pentamethylcyclopentadienylsodium, [NaC10H15] (NaCp*), has been determined from high-resolution X-ray powder diffraction. The compound crystallizes in space group Cmcm with lattice parameters a = 4.61030 (3), b = 16.4621 (3), c = 14.6751 (2) A, V = 1113.77 (4) A(3) (Z = 4). NaCp* forms polymeric multidecker chains along the a axis. The Rietveld refinement (R(p) = 0.050 and R(F) = 0.163) shows that the Cp* moieties occupy, with disorder, two different orientations rotated away from the eclipsed conformation by +/-13.8 degrees.

Chiral metal-dithiolene/viologen ion pairs: synthesis and electrical conductivity.

Enantiomerically pure dithiolene complexes NBu4[Ni[(R,R)-diotte)2] and NBu4[Ni((S,S)-diotte]2] (diotte2- = a 1,3-dioxolane-tetrathiaethylene), were prepared from the corresponding enantiomers of a diotte2- precursor. The structure of the precursor was solved by single-crystal X-ray analysis; desulfurization afforded a novel tetrathiafulvalene derivative. Combination of the complex monoanion with the enantiomers of the viologen derivative bis(2-methyl-3-hydroxypropyl)-4,4'-dipyridinium (HiBV2+) afforded enantiomeric and diastereomeric ion-pair complexes of the type HiBV[Ni(diotte)2]2. For comparison, the analogous compounds A[Ni(diotte)2]2, (A2+ = methyl (MV2+), octyl (OV2-), stearyl (StV2+) viologen or two 2,2'-bipyridinium acceptors), HiBV-[Ni(diotte)L] [L = mnt2- (maleonitrile-1,2-dithiolate), dmit2- (2-thioxo-1,3-dithiol-4,5-dithiolate)], MV[Ni(dmit)2)]2, [Ni(diotte)2], and [Ni(diotte)(dmit)] were synthesized. An X-ray powder diffraction structural analysis of MV-[Ni(dmit)2)]2 revealed the presence of mixed stacks that contain the sequence anion-anion-cation. While no short contacts are observable within a stack, these are observed between the stacks for the dication-anion interaction by short S...H distances in the range of 2.77 to 2.86 A, and for the anion-anion interaction short S...S distances of 3.55 to 3.65 A. In agreement with the absence of intrastack interactions, no ion-pair charge-transfer band can be detected in this and the other complexes. ESR and UV/Vis data suggest that in [Ni(diotte)2]- electron delocalization is less pronounced than in the corresponding mnt2- and dmit2- complexes. The specific electrical conductivity (sigma) of pressed powder pellets ranges from 10(-2) to 10(-12) ohm(-1) cm(-1) and in all cases increases with increasing temperature (293 - 393 K) according to an Arrhenius law. Corresponding activation energies vary from 0.14 to 0.93 eV and increase linearly with log a for structurally similar ion pairs. Charge generation is postulated to occur by disproportionation of the monoanion as suggested by the almost linear increase of log(sigma) with decreasing disproportionation energy. The conductivity of diastereomers of ions with two unlike configurations like [(S,S)-HiBV]-[Ni[(R,R)-diotte]2]2 (1.1 x 10(-1) ohm(-1) cm(-1)) is one to two orders of magnitude higher as compared to the diastereomers with two like-configured ions.

Structural characterization of three crystalline modifications of telmisartan by single crystal and high-resolution X-ray powder diffraction.

Three crystalline modifications (A, B, and C) of 4'-[[2-n-propyl-4-methyl-6-(1-methyl-benzimidazol-2-yl)benzi midazol-1-yl]methyl]biphenyl-2-carboxylic acid (INN name, telmisartan) have been detected and their crystal structures have been determined by single-crystal X-ray diffraction (pseudopolymorph C) and the method of simulated annealing from high-resolution X-ray powder diffraction data (polymorphs A and B). The compound is of interest because of its use as an angiotensin II receptor antagonist. Polymorph A crystallizes in space group P2(I)/c, Z = 4, with unit cell parameters a = 18.7798(3), b = 18.1043(2), and c = 8.00578(7) A, beta = 97.066(1) degrees, and V = 2701.31 A(3). Polymorph B crystallizes in space group P2(I)/a, Z = 4, with unit cell parameters a = 16.0646(5), b = 13.0909(3), and c = 13.3231(3) A, beta = 99.402(1) degrees, and V = 2764.2(1) A(3). The solvated form C crystallizes in space group C2/c, Z = 8, with unit cell parameters a = 30.990(5), b = 13.130(3), and c = 16.381(3) A, beta = 95.02(2) degrees, and V = 6639(2) A(3). For the structure solutions of polymorphs A and B, 13 degrees of freedom (3 translational, 3 orientational, 7 torsion angles) were determined in approximately 2 h of computer time, demonstrating that the crystal packing and the molecular conformation of medium-sized (MW approximately 500) pharmaceutical compounds can now be solved quickly and routinely from high-resolution X-ray powder diffraction data.

Powder Structure Solutions of the Compounds Potassium Phenoxide-Phenol: C(6)H(5)OK.xC(6)H(5)OH (x = 2, 3).

We report the ab initio structure solutions of two solvent containing potassium phenoxides by high-resolution powder X-ray diffraction. Both compounds are of interest for the classification of the mechanism of Kolbe-Schmitt type reactions. C(6)H(5)OK.2C(6)H(5)OH crystallizes in space group Abm2, Z = 4, with unit cell parameters a = 10.12458(4) Å, b = 21.2413(1) Å, c = 7.89784(3) Å. C(6)H(5)OK.3C(6)H(5)OH crystallizes in space group Pbca, Z = 8, with unit cell parameters a = 22.7713(1) Å, b = 25.4479(2) Å, c = 7.75549(4) Å. Both compounds show polymeric zigzag chains [K([6])O(2)([2])O([1])pi(phenyl)([1])] aligned along the c-axis. The coordination of the potassium ions is similar for both compounds. They lie at the center of distorted octahedra of five oxygen atoms and one phenyl ring, which donates its pi electrons. The distortion decreases as the number of free phenol increases.

Novel Alkali-Metal Coordination in Phenoxides: Powder Diffraction Results on C(6)H(5)OM (M = Li, Na, K, Rb, Cs).

We report the ab initio structure solutions of C(6)H(5)OM (M = K, Rb, Cs) by high-resolution powder X-ray diffraction. The compounds, which are of interest for reactions of the Kolbe-Schmitt type, are isostructural. The crystal structures are orthorhombic, space group Pna2(1), Z = 12, with lattice parameters (a, b, c in Å) 14.1003(1), 17.9121(1), and 7.16475(1) for the K compound, 14.4166(2), 18.2028(2), and 7.4009(1) for the Rb compound, and 14.8448(2), 18.5070(2), and 7.6306(1) for the Cs compound. They have a chain structure [M([6])] along the crystallographic c axis. This is a very unusual arrangement in which two different alkali-metal coordination spheres are observed: a distorted octahedron and a 3-fold oxygen coordination. In the latter, the 3-fold-coordinated unsaturated alkali metals additionally show weak interactions with phenyl rings. We also give powder patterns for the compounds with M = Li, Na. The former crystallizes in the monoclinic space group P2(1)/a with lattice parameters a = 22.594 Å, b = 4.7459 Å, c= 10.053 Å, and beta = 97.82 degrees with Z = 8, but no structure solution was possible. The powder pattern for the Na phenolate is in agreement with the earlier single-crystal structure.

Characterization of the products of the heme detoxification pathway in malarial late trophozoites by X-ray diffraction.

In a process inhibited by the quinoline antimalarial drugs, Plasmodia detoxify heme released during the degradation of hemoglobin by aggregating it into malarial pigment, an insoluble crystalline heme coordination polymer. Synchrotron x-ray powder diffraction patterns for intact desiccated malarial trophozoites and synthetic beta-hematin have been measured; both materials correspond to a single crystalline triclinic lattice with unit cell parameters a = 12.2176(4), b = 14.7184(5), c = 8.0456(3) A; alpha = 90.200(2), beta = 96.806(3), gamma = 97.818(3) degrees and Z = 2. These results unambiguously demonstrate that hemozoin crystallites are identical to synthetic beta-hematin.