The tetragonal phase of Fe 1+ Se (0.01 ≤  ≤ 0.04) with the anti-PbO-type crystal structure displays superconductivity (T c ~ 8.5 K) when  = 0.01 and the superconductivity is destroyed by additional interstitial Fe. 9 The compound bears close structural resemblance to LiFeAs 10 (both compounds contain FeQ 4 (Q = Se, As) tetrahedra that are highly compressed in the basal plane compared with other iron-based superconductors) and both compounds differ from the canonical iron-based superconducting system in that they superconduct when as close to stoichiometric as possible (i. The lithium/ammonia solutions were rapidly decolourised by Fe 1+ Se at -78 °C. This is consistent either with the classic method for decomposing the metastable solution of solvated electrons using a "rusty nail" as a catalyst for the formation of lithium amide and hydrogen, or it indicates. Donation of the solvated electrons from the alkali metal ammonia solution to empty bands in the solid with Li ions co-inserted to balance the charge in a reductive intercalation reaction. The product was a black powder with a much finer grain size than the parent Fe 1+ Se material. The products were extremely air sensitive. X-ray powder diffraction (XRPD) showed no evidence for the starting material or other products above the 5% level and the diffraction peaks were indexed on a body centred tetragonal unit cell with lattice parameters a = 3.8249(2) Å and c = 16.5266(9) Å at room temperature. The basal lattice parameter, a (= √2 × Fe-Fe distance) is 1.4% larger than the value of 3.7734(1) Å reported for Fe 1.01 Se. 9 The c lattice parameter of 16.5266 (9) Neutron powder diffraction (NPD) patterns were collected from samples synthesised using 0.5 moles of Li per mole of FeSe with either NH 3 or ND 3 as solvent. The XRPD patterns of these products were similar, but their NPD patterns were dramatically different (the intensities varied greatly between the two compounds because of the greatly different neutron scattering lengths for H (-3.74 fm) and D (+6.67 fm), and the H-containing material produced a characteristic incoherent background) proving that the samples contain H(D). A structural model was obtained from the deuterated sample by starting from the model suggested by the X-ray refinements with N in the site 8-coordinate by Se and computing Fourier difference maps to reveal the remaining nuclear scattering density. Refinements against data from the GEM diffractometer at room temperature and the HRPD diffractometer at 8 K on the same sample of deuterated material produced similar structural models at the two temperatures. The initial assumption of a formula (LiND 2 )Fe 2 Se 2 resulted in an apparently satisfactory fit to the low temperature HRPD data (which emphasises the short d-spacing data) using a model in which the D atoms were located on crystallographic positions (16m site: (x, x, z)) which refined freely to be about 1 Å from the N atom (2a site: (0, 0, 0)) and with the N-D bonds directed towards the selenide anions. In this initial model the...

The interplay and coexistence of superconducting, magnetic and structural order parameters in NaFe1−xCoxAs has been studied using SQUID magnetometry, muon-spin rotation and synchrotron x-ray powder diffraction. Substituting Fe by Co weakens the ordered magnetic state through both a suppression of TN and a reduction in the size of the ordered moment. Upon further substitution of Fe by Co the high sensitivity of the muon as a local magnetic probe reveals a magnetically disordered phase, in which the size of the moment continues to decrease and falls to zero around the same point at which the magnetically-driven structural distortion is no longer resolvable. Both magnetism and the structural distortion are weakened as the robust superconducting state is established.

The structure and Li + ion dynamics of a new class of ABO 3 perovskite with Li on both the A-and B-sites are described. La 3 Li 3 W 2 O 12 is synthesized by solid state reaction at 900 °C and shown by powder X-ray diffraction to adopt the structure of a monoclinic double perovskite (A 2 )BB′O 6 , (La 1.5 Li 0.5 )WLiO 6 , with rock salt order of W 6+ and Li + on the B-site. High resolution powder neutron diffraction locates A-site Li in a distorted tetrahedron displaced from the conventional perovskite A-site, which differs considerably from the sites occupied by Li in the well studied La 2/3−x Li 3x TiO 3 family. This is confirmed by the observation of a lower coordinated Li + ion in the 6 Li magic angle spinning nuclear magnetic resonance (NMR) spectra, in addition to the B-site LiO 6 , and supported computationally by density functional theory (DFT), which also suggests local order of A-site La 3+ and Li + . DFT shows that the vacancies necessary for transport can arise from Frenkel or La excess defects, with an energetic cost of ∼0.4 eV/vacancy in both cases. Ab initio molecular dynamics establishes that the Li + ion dynamics occur by a pathway involving a series of multiple localized Li hops between two neighboring A-sites with an overall energy barrier of ∼0.25 eV, with additional possible pathways involving Li exchange between the A-and B-sites. A similar activation energy for Li + ion mobility (∼0.3 eV) was obtained from variable temperature 6 Li and 7 Li line narrowing and relaxometry NMR experiments, suggesting that the barrier to Li hopping between sites in La 3 Li 3 W 2 O 12 is comparable to the best oxide Li + ion conductors. AC impedance-derived conductivities confirm that Li + ions are mobile but that the long-range Li + diffusion has a higher barrier (∼0.5 eV) which may be associated with blocking of transport by A-site La 3+ ions.

Two quaternary transition-metal cyanamides with a novel crystal structure are stabilised through cyanamide tilts and octahedral twists.

(NBT), BaTiO 3 (BTO), and K 0.5 Bi 0.5 TiO 3 (KBT) are known but all have inferior properties to PZT. [ 2,3,5 ] Bi 3+ has a 6s 2 confi guration with crystal chemistry similar to that of Pb 2+ , and bismuthbased perovskites are attractive as they can offer high Curie and depolarization temperatures required for demanding application environments. [ 5,6 ] [ 9 ] which can be converted into a long-range polarization along this direction by the introduction of LaFeO 3 (LFO) which itself has antiferrodistortive [110] p displacements, although this orthorhombic O [110] The perovskite oxide lead zirconate titanate (PbZr 1− x Ti x O 3 ) (PZT) has extraordinary electromechanical properties at the morphotropic phase boundary (MPB), [ 1 ] making modifi ed PZT ceramics the basis for almost all actuators, sensors and related applications in use today. The MPB in the PZT solid solution occurs near x ≈ 0.48 [ 1 ] between the ferroelectric rhombohedral ( R 3 m , denoted as R [111] ) and tetragonal ( P 4 mm , denoted as T [001] ) phases, with polarizations lying along the [111] p body diagonal and [001] p edge of the primitive ≈ 4 Å ABO 3 perovskite unit cell, respectively. [1][2][3] The PZT phases are untilted and the R [111] and T [001] structures are described crystallographically, using a modifi ed Glazer notation, as a a a + , respectively, where the subscript indicates ferroelectric displacement and the superscript the nature of the octahedral tilting with respect to the primitive unit cell axes. [ 4 ] It is challenging to create an MPB in a bismuth-based lead-free system as it has proved diffi cult to prepare phases with polarization directed along the [001] p primitive cell edge in such materials. Several Pb-free MPB systems based on K 0.5 Na 0.5 NbO 3 , Na 0.5 Bi 0.5 TiO 3

Layered bismuth oxides exhibit a broad range of tunable physical properties as a result of their excellent structural versatility which facilitates compositional substitutions at both cationic and anionic positions. Here we expand this family in a new direction through the preparation of the first example of a bismuth-containing oxide carbodiimide, Bi2O2NCN, which assumes an extended variant of the anti-ThCr2Si2 structure-type adopted by Bi2O2 Ch (Ch = Se or Te) oxide chalcogenides. Electronic structure calculations reveal the title compound to be an indirect band gap semiconductor with a band gap of approximately 1.4 eV, in good agreement with the measured value of 1.8 eV, and intermediate between that of structurally related Bi2O2S (1.12 eV) and β-Bi2O3 (2.48 eV). Mott–Schottky experiments demonstrate Bi2O2NCN to be an n-type semiconductor with a conduction band edge position of −0.37 V vs reversible hydrogen electrode. This study highlights the pseudochalcogenide nature of the –NCN– carbodiimide anion, which may be substituted in place of oxide or chalcogenide anions in this and potentially other structural classes as an effective means of electronic tuning.

High-resolution X-ray and neutron powder diffraction are used to reveal details of the spin-reorientation transition in the layered oxide pnictide CeMnAsO. Above 38 K, the localized moments on Mn(2+) are antiferromagnetically ordered in a checkerboard fashion within the antifluorite-type MnAs planes and are oriented perpendicular to the planes. Below 38 K, reorientation of these moments into the planes commences. This is complete by 34 K and is coincident with long-range ordering of the Ce(3+) moments. The Ce(3+) and Mn(2+) moments have an arrangement that is different in detail from that in the isostructural NdMnAsO and PrMnSbO. There is no evidence for structural distortion, as found for PrMnSbO and related Pr(3+)-containing compounds, although there is evidence for a very slight (0.025%) misfit between the magnetic and structural cells below the spin-reorientation transition. It is clarified that neutron powder diffraction methods are unable to distinguish between collinear and noncollinear arrangements of manganese and lanthanide moments when the moments have a component parallel to the MnAs planes. A proposal from computational analysis that NdMnAsO and CeMnAsO should adopt different magnetic structures on the basis of the different balances between biquadratic and antisymmetric exchange interactions should be tested using alternative methods.

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d cations above room temperature in the AFeO system. We report the synthesis of a polar corundum GaFeO by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO-type GaFeO under the synthesis conditions. The A/Fe cations are shown to be more ordered in polar corundum GaFeO than in isostructural ScFeO. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO exhibits weak ferromagnetism at room temperature that arises from its FeO-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.