We report hard (14 keV) x-ray diffraction measurements on three compositions (x=0.11,0.12,0.13) of the high-temperature superconductor La2-xSrxCuO4. All samples show charge-density-wave (CDW) order with onset temperatures in range 51-80 K and ordering wavevectors close to (0.23,0,0.5). The CDW is strongest longest in-plane correlation length near 1/8 doping. On entering superconducting state suppressed, demonstrating strong competition between charge superconductivity. coexists...

We present new results on the microscopic nature of ferroelectricity mechanisms in ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Ca}}_{3}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$. To first approximation, we confirm hybrid improper ferroelectric mechanism recently proposed by Benedek Fennie for these Ruddlesden-Popper compounds. However, find that there is a complex competition between lattice modes different symmetry which leads to phase coexistence over large temperature range...

By using a symmetry motivated basis to evaluate local distortions against pair distribution function data, we show without prior bias, that the off-center Ti displacements in archetypal ferroelectric BaTiO3 are zone centered and rhombohedral-like across its known paraelectric phases. We construct simple Monte Carlo model captures our main experimental findings demonstrate how rich crystallographic phase diagram of emerges from correlations symmetry-breaking alone. Our results strongly...

The central goal of crystal engineering is to control material function via rational design structure. A particularly successful realisation this paradigm hybrid improper ferroelectricity in layered perovskite materials, where layering and cooperative octahedral tilts combine break inversion symmetry. However, the parent family inorganic ABX3 perovskites, symmetry prevents coupling polar distortions. Here, we use group-theoretical analysis uncover a profound enhancement number ferroelectric...

Electronic structure calculations of the Verwey ground state magnetite, Fe${}_{3}$O${}_{4}$, using density functional theory with treatment on-site Coulomb interactions (DFT+U scheme), are reported. These use recently published experimental crystal coordinates for magnetite in monoclinic space group $Cc$. The computed distribution minority spin electron states close to Fermi level demonstrates that charge order and Fe${}^{2+}$-orbital present at $B$-type lattice sites a first approximation....

The layered perovskite Ca3-xSrxMn2O7 is shown to exhibit a switching from material exhibiting uniaxial negative positive thermal expansion as function of x. be related two closely competing phases with different symmetries. (NTE) effect maximized when the solid solution tuned closest this region phase space but switched off suddenly on passing though transition. Our results show for first time that, by understanding symmetry alone, one may achieve unprecedented chemical control unusual property.

We report a new nickel hydroxyfluoride diaspore Ni(OH)F prepared using hydrothermal synthesis from NiCl2·6H2O and NaF. Magnetic characterization reveals that, contrary to other reported transition-metal diaspores, displays weak ferromagnetism below the magnetic ordering temperature. To understand this difference, neutron diffraction is used determine long-range structure. The structure found be distinct those for diaspores shows an antiferromagnetic spin in which ferromagnetic canting...

The thermal evolution of electronic order in the complex Verwey ground state magnetite $(\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4})$ has been determined through 22 high-accuracy synchrotron x-ray structure refinements using three $10--40\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ grains stoichiometric magnetite. A robust fitting function is introduced to extract values parameterlike quantities at zero temperature and upper limit phase...

Abstract Why is it that ABO 3 perovskites generally do not exhibit negative thermal expansion (NTE) over a wide temperature range, whereas layered of the same chemical family often do? It accepted there are two key ingredients determine extent NTE: presence soft phonon modes drive contraction (have Grüneisen parameters); and anisotropic elastic compliance predisposes material to deformations required for NTE along specific axis. This difference in properties surprising since both possess...

The cooperative tilting distortions of n = 2 Ruddlesden–Popper oxides can be utilized to break the inversion symmetry host lattice and induce ferroelectric behavior. Unfortunately desired a–a–c+/a–a–c+ structural deformation is only stabilized in phases with extremely small tolerance factors, limiting chemical scope this breaking approach. Here we describe influence topochemical fluorination on demonstrate that conversion La3Ni2O7 La3Ni2O5.5F3.5 breaks perovskite double layers which...

We show that the valence electrons of ${\mathrm{Ba}}_{3}{\mathrm{NaRu}}_{2}{\mathrm{O}}_{9}$, which has a quasimolecular structure, completely crystallize below 210 K. Using an extended Hubbard model, we charge ordering instability results from long-range Coulomb interactions. However, orbital ordering, metal-metal bonding, and formation partial spin gap enforce magnitude separation. The striped order frustrated hcp lattice ${\mathrm{Ru}}_{2}{\mathrm{O}}_{9}$ dimers lead to competition with...

Cation ordering in the 1322 perovskite CaCu3Fe2Nb2O12 has been investigated by synchrotron X-ray diffraction structure analysis, high-resolution electron microscopy, and magnetic measurements. All of samples have full 1:3 Ca Cu cations at A-sites, but Fe Nb B sites show different degrees depending on synthesis conditions. A slow-cooled sample almost complete rock-salt-type 1:1 cation sites, a rapidly cooled no long-range B-cation arrangement. The ordered compound shows large saturated...

A group-theoretical approach is used to enumerate the possible couplings between magnetism and ferroelectric polarization in parent Pm{\overline 3}m perovskite structure. It shown that third-order magnetoelectric coupling terms must always involve magnetic ordering at B sites which either transforms both as R-point or X-point time-odd irreducible representations (irreps). For fourth-order it demonstrated this criterion may be relaxed allowing involving irreps X-, M- R-points collectively...

Polar metals are an intriguing class of materials in which electric polarisation and metallicity can coexist within a single phase. The unique properties polar challenge expectations, making way for the exploration exotic phenomena such as unconventional magnetism, hyperferroelectric multiferroicity developing multifunctional devices that leverage both polarization its asymmetry spin conductivity, arises due to Rashba effect. Here, via high pressure crystal diffraction study, we report...

The interplay between crystallographic symmetry, structural distortions, and the tolerance factor derived from isotropic ionic radii of constituent cations anions inorganic perovskites related materials is a ubiquitous concept in solid-state chemistry. Here we demonstrate model for phase transition temperatures associated with these distortions layered by considering anisotropy cations, which are susceptible to first-order Jahn-Teller distortions. These symmetry-lowering transitions known...

A variable-temperature and pressure single-crystal diffraction study of hybrid improper ferroelectric Sr 3 Sn 2 O 7 is reported. In combination with symmetry analysis, we reveal that the application temperature induce distinct phase transition pathways, driven by a differing response octahedral rotations to these stimuli. Contrary what has been previously predicted, observe paraelectric between 10.17(18) 12.13(14) GPa, meaning remains stable significantly higher pressures than expected.

Polar metals are an intriguing class of materials that feature a polar crystal structure while also exhibiting metallic conductivity. The unique properties challenge expectations, making way for the exploration exotic phenomena such as unconventional magnetism, hyperferroelectric multiferroicity, and development multifunctional devices can leverage both material's its asymmetry in spin conductivity, arises due to Rashba effect. Here, via high-pressure single-crystal diffraction study, we...

Dense metastable phases obtained under "hard" high-pressure conditions may contain instabilities such as unusual oxidation states or coordination environments that be partially relieved by "soft" low-temperature chemistry. The synthesis of SrCrO2.8 (see picture, left) and SrCrO2.75 (right) from the perovskite SrCrO3 leads to a relaxation around Cr4+ octahedral tetrahedral.

The magnetic and crystal structures of the title materials have been investigated using high-resolution neutron synchrotron x-ray powder diffraction. Ferromagnetic Ru dimers are observed in spin-ordered ground states all three materials, evidencing an intradimer double exchange interaction. Antiferromagnetic order between breaks degeneracy triangular lattice but no distortion ${B}^{\ensuremath{'}}=\mathrm{La}$ Y is observed. ordering transition temperature increases with radius...

Abstract The tetragonal tungsten bronze, Sr 2 NaNb 5 O 15 , shows promise for application in high-temperature high-efficiency capacitors vital the sustainable energy revolution. Previously, structural complexity of this and related materials has obscured mechanisms underpinning two large anomalies relative permittivity ( ε r ) which give rise to their exceptionally broad dielectric response. Here, we comprehensively investigate evolution from −173 627 °C, combining electron, X-ray neutron...

By tuning the tolerance factor, t, of Ruddlesden–Popper oxide Ca2MnO4 through isovalent substitutions, we show that uniaxial coefficient linear thermal expansion (CLTE) these systems can be systematically changed large negative to positive values. High-resolution X-ray diffraction measurements magnitude (NTE) increases as t decreases across stability window NTE phase. Transitions phases with (PTE) are found occur at both high-t and low-t limits stability. First-principles calculations...

The phonon–glass electron crystal concept is one of the key guiding principles for development efficient thermoelectric materials. Here, we confirm that SrTiO3 becomes a large numbers A-site vacancies in Sr1–xLa0.67x□0.33xTiO3 series and show its properties are stymied by presence core–shell grain structure. Thermal conductivity, heat capacity, neutron powder diffraction, complemented representational analysis phonon calculations, were used to investigate thermal transport. This reveals...