Temperature-dependent X-ray Powder Diffraction Research Articles

Confined-Melting-Assisted Synthesis of Bismuth Silicate Glass-Ceramic Nanoparticles: Formation and Optical Thermometry Investigation.

Bismuth-based (nano)materials have been attracting increasing interest due to appealing properties such as high refractive indexes, intrinsic opacity, and structural distortions due to the stereochemistry of 6s2 lone pair electrons of Bi3+. However, the control over specific phases and strategies able to stabilize uniform bismuth-based (nano)materials is still a challenge. In this study, we employed the ability of bismuth to lower the melting point of silica to introduce a new synthetic approach able to confine the growth of bismuth-oxide-based materials into nanostructures. Combining in situ temperature-dependent synchrotron radiation X-ray powder diffraction (XRPD) with high-resolution transmission electron microscopy (HR-TEM) analyses, we demonstrate the evolution of a confined Bi2O3-SiO2 nanosystem from Bi2SiO5 to Bi4Si3O12 through a melting process. The silica shell acts as both a nanoreactor and a silicon source for the stabilization of bismuth silicate glass-ceramic nanocrystals keeping the original spherical shape. The exciton peak of Bi2SiO5 is measured for the first time allowing the estimation of its real energy gap. Moreover, based on a detailed spectroscopic investigation, we discuss the potential and the limitations of Nd3+-activated bismuth silicate systems as ratiometric thermometers. The synthetic strategy introduced here could be further explored to stabilize other bismuth-oxide-based materials, opening the way toward the growth of well-defined glass-ceramic nanoparticles.

Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd

Crystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.

A hybrid molecular rotor crystal with dielectric relaxation and thermochromic luminescence

Herein, we reported a hybrid crystals, [C3-Mim][PbBr3] (1) where C3-Mim+ = 1-propyl-3-methylimidazolium, this compound shows two steps solid-solid phase transition at 256 and 359 K, respectively. The first phase transition is related to the strong thermal vibrations of the crystal lattice, and the alkyl chain rotation motion on a single axis of organic cations can be observed from the temperature dependent crystal structure. The second step phase transition were proved by temperature dependent powder X-ray diffraction and accompanied by remarkable dielectric relaxation. In addition, the temperature-dependent photoluminescent indicated two emission bands from organic and inorganic component have different sensitivity to temperature, leading to 1 showing photoluminescent thermochromism, which may have potential application in the thermosensitive devices.

Reversible Thermochromism and Strong Ferromagnetism in Two-Dimensional Hybrid Perovskites.

Two-dimensional (2D) hybrid perovskites have shown many attractive properties associated with their soft lattices and multiple quantum well structure. Herein, we report the synthesis and characterization of two new multifunctional 2D hybrid perovskites, (PED)CuCl4 and (BED)2 CuCl6 , which show reversible thermochromic behavior, dramatic temperature-dependent conductivity change, and strong ferromagnetism. Upon temperature change, the (PED)CuCl4 and (BED)2 CuCl6 crystals exhibit a reversible color change between yellow and red-brown. The associated structural changes were monitored by in situ temperature-dependent powder X-ray diffraction (PXRD). The (BED)2 CuCl6 exhibits superior thermal stability, with a thermochromic working temperature up to 443 K. The conductivity of (BED)2 CuCl6 changes over six orders of magnitude upon temperature change. The 2D perovskites exhibit ferromagnetic properties with Curie temperatures around 13 K.

Reversible Thermochromism of Nickel(II) Complexes and Single-Crystal-to-Single-Crystal Transformation.

A molecular Ni(II)–NNN pincer complex (1) exhibited unprecedented reversible single-crystal-to-single-crystal transformation and color change upon heating and cooling due to a subtle change in the N–Ni(II) bond length and ligand conformation. UV–vis, thermogravimetric, differential scanning calorimetry, single-crystal structural data, temperature-dependent powder X-ray diffraction, and Raman and computational studies supported the structural change of the Ni(II) complex with temperature.

An Old Dog with New Tricks - Additions to the Cesium Lithium Chloride System: Cs3Li2Cl5 and the Hydrated Cs3LiCl4 · 4H2O.

The CsCl/LiCl system has been studied for over a century now. Numerous phases have been predicted - only three have hitherto been found. We present the synthesis and single-crystal structure of the cesium lithium pentachloride Cs3Li2Cl5, predicted earlier but with a different structure. The anhydrous new phase readily reacts to Cs3LiCl4 · 4H2O in air. The tetrahydrate can also be obtained through the simplest, most inexpensive and green synthesis possible: an immediate, room-temperature mechanosynthesis from only CsCl and LiCl (3 : 1) in air. Differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA), as well as in situ temperature-dependent powder X-ray diffraction studies on this second ever reported ternary alkali chloride hydrate allowed for a revision of the CsCl/LiCl phase diagram. Density of states and total energy calculations further elucidate the new alkali chlorides and update the relative stability of previous structure predictions.

Ethanol- and Methanol-Coordinated and Solvent-Free Dodecahydro closo-Dodecaborates of 3d Transition Metals and of Magnesium

Magnesium and 3d transition metals closo-borates were prepared by mechanosynthesis (ball milling) of the mixtures Na2B12H12 + MCl2 (M = Mn, Fe, Co, Ni, Mg), followed by addition of ethanol or methanol and drying under dynamic vacuum. The dead mass of NaCl is partly removed by filtration. The crystal structures of solvent-coordinated and solvent-free closo-borates have been characterized by temperature dependent synchrotron radiation X-ray powder diffraction, ab initio calculations, thermal analysis and infrared spectroscopy. Various solvated complexes containing six, four, three, two or one solvent molecules were obtained by successive removal of the solvent until in most case the solvent-free metal closo-borates were obtained with the exception of Mg whose hypothetical crystal structure, however, could have its prototype in MnB12H12. The 3d transition metal closo-borates were studied in the view of their potential use as Na- or Li-ion battery electrodes in combination with Na or Li closo-borate solid electrolytes. The metal oxidation state (II) obtained in compounds presented here does not allow such application.

Lead(II) oxidotellurates(VI) with double perovskite structures

Pb2BTeO6 (B = Co, Mn, Cd, Ca) and Pb7.47Sr3.53Te4O23 were synthesized by solid state reactions, starting from TeO2, and precursors of lead(II) oxide and the respective metal oxides. Structure determinations from single crystal X-ray data at room temperature revealed that Pb2CoTeO6 and Pb2CoTeO6 adopt the B site ordered cubic double perovskite aristotype (Z = 4, Fm3¯m) whereas Pb2CdTeO6 and Pb2CaTeO6 crystallize as hettotypes thereof, with a reduction of the space group symmetry to C2/c and P21/c, respectively. Differential scanning calorimetry and temperature-dependent X-ray powder diffraction revealed reversible phase transitions around 270 °C for Pb2CdTeO6 and 225 °C for Pb2CaTeO6 to the cubic aristotype as the high-temperature phase. Pb7.47Sr3.53Te4O23 is a representative of a solid solution M11Te4O23 (M = Pb, Sr) with Sr2+ and Pb2+ cations occupationally disordered at the same sites in the cubic structure (Z = 8, Fm3¯m). Its crystal structure can be described as an eightfold superstructure with all axes doubled in relation to the fully ordered double perovskite structure, and with cation vacancies at one of the B sites, anion vacancies at one of the O sites, and an additional O site in the structure. The relationships between the aristotype structure and the different hettotypes (Pb2CdTeO6, Pb2CaTeO6 and M11Te4O23 (or M2.75TeO5.75 with Z = 32)) are concisely described with the aid of group-subgroup relations.

Study of mixed-valence Mn2BO4 using XRD, XPS and XAFS spectroscopies

The valence states and local structure around Mn atoms in mixed-valence Mn2BO4 have been studied by temperature dependent X-ray powder diffraction (XRPD), X-ray photoelectron (XPS) and Mn K-edge X-ray absorption (XAFS) spectroscopies measurements. X-ray absorption near-edge structure (XANES) and XPS have been used to measure the average oxidation state of Mn in bulk and near-surface of the material. The edge position, peak shapes and pre-edge features of Mn K-edge XANES spectra have been discussed. The pronounced temperature dependence of the Debye-Waller (DW) factor corresponding to the MnO coordination shell has been found from the extended x-ray absorption fine structure (EXAFS) analysis and has been associated with variations in the local distortions in MnO6 octahedra and emergence of short-range magnetic correlations at low temperatures. The XRPD measurements have been carried out at 298, 523 and 773 K. The monoclinic symmetry (P21/n) was found to persist up to highest temperature measured. The BVS calculations have revealed large valence difference between two manganese sites that strongly supports the presence of charge ordering up to high temperatures.

Hydrated and anhydrous dodecahydro closo-dodecaborates of 3d transition metals and of magnesium

Magnesium and 3d transition metals closo-dodecaborates were prepared by mechanosynthesis (ball milling) of the mixtures Na2B12H12 + MCl2 (M = Ti, Cr, Mn, Fe, Co, Cu, Zn, Mg) and CuCl, followed by hydration and drying under dynamic vacuum. The crystal structures of hydrated and anhydrous closo-dodecaborates have been characterized by temperature dependent synchrotron radiation X-ray powder diffraction, ab initio calculations, thermal analysis and infrared spectroscopy. Three different complexes containing water were found: a homoleptic octahedral complex in M(H2O)6B12H12 crystallizing in three different deformation variants of the complex centred closo-dodecaborate cube, a heteroleptic octahedral complex in M(H2O)4B12H12 containing four water molecules and two hydrogens from a closo-dodecaborate centring also a deformed closo-dodecaborate cube, and a heteroleptic octahedral complex in Fe(H2O)2B12H12 containing two water molecules where four hydrogen atoms are bridging two closo-dodecaborates. Anhydrous cobalt(II) and copper(I) closo-dodecaborates were obtained by drying the hydrated sample under dynamic vacuum. Both compounds crystallize with bcc packing of closo-dodecaborates where the metal is in octahedral coordination by hydrogen H6 for cobalt, and a tetrahedral coordination H4 is found for copper, bridging two closo-dodecaborates in an infinite chain. The orbital overlap between transition metal and closo-anion leads to directional covalent bonding. While CoB12H12 has trigonal symmetry (R3) allowing for an ordered metal position, Cu2B12H12 follows the cubic symmetry of bcc packing, which leads to a disordered metal position. The structure of NiB12H12, originally published as monoclinic (I2), is revised based on the trigonal structural model of CoB12H12.

Bi2SiO5@g-SiO2 upconverting nanoparticles: a bismuth-driven core-shell self-assembly mechanism.

Core-shell systems have attracted increasing interest among the research community in recent years due to their unique properties and structural features, and the development of new synthetic strategies is still a challenge. In this work, we have investigated lanthanide-doped Bi2SiO5 nanocrystal formation inside mesoporous silica nanoparticles (MSNs). The role of both synthesis temperature and concentration of the bismuth precursor impregnated into the MSNs is discussed, showing an unprecedented strategy for the simultaneous stabilization of a crystalline core and a glassy shell. Temperature dependent synchrotron radiation X-ray powder diffraction (SR-XRPD) and high resolution transmission electron microscopy (HR-TEM) analyses allow one to follow the crystalline core growth. A mechanism for the formation of a Bi2SiO5@g-SiO2 core-shell nanosystem is proposed. In addition, the easy tunability of the color output of the upconverting system is demonstrated by means of suitable doping lanthanide ions with potential applications in several fields.

Unusual adsorption behaviours and responsive structural dynamics via selective gate effects of an hourglass porous metal-organic framework.

An hourglass porous metal–organic framework, LIFM-12, constructed on a T-shaped flexible ligand with Cu2+ paddle-wheel clusters, shows temperature and gas adsorption responsive structural dynamics upon reversible molecular guest binding. Temperature-dependent single crystal and powder X-ray diffraction experiments show that the open gate status of the framework with adaptive behaviours facilitates kinetic diffusion of gas molecules resulting in the sequential filling of pores of different sizes, thus creating a breathing behaviour reminiscent of the observation of several steps in adsorption isotherms. In addition, adsorption studies revealed that LIFM-12 performs exceptional adsorption selectivity of 10–25 for CO2versus light gases N2, CH4, and CO and up to 200 for C3H6versus CH4.

Accumulation of Glassy Poly(ethylene oxide) Anchored in a Covalent Organic Framework as a Solid-State Li+ Electrolyte.

Design of molecular structures showing fast ion conductive/transport pathways in the solid state has been a significant challenge. The amorphous or glassy phase in organic polymers works well for fast ion conductivity because of their dynamic and random structure. However, the main issue with these polymers has been the difficulty in elucidating the mechanisms of ion conduction and thus low designability. Furthermore, the amorphous or glassy state of ion conductive polymers often confronts the problems of structural/mechanical stabilities. Covalent organic frameworks (COFs) are an emerging class of crystalline organic polymers with periodic structure and tunable functionality, which exhibit potential as a unique ion conductor/transporter. Here, we describe the use of a COF as a medium for all-solid-state Li+ conductivity. A bottom-up self-assembly approach was applied to covalently reticulate the flexible, bulky, and glassy poly(ethylene oxide) (PEO) moieties that can solvate Li+ for fast transport by their segmental motion in the rigid two-dimensional COF architectures. Temperature-dependent powder X-ray diffraction and thermogravimetric analysis showed that the periodic structures are intact even above 300 °C, and differential scanning calorimetry and solid-state NMR revealed that the accumulated PEO chains are highly dynamic and exhibit a glassy state. Li+ conductivity was found to depend on the dynamics and length of PEO chains in the crystalline states, and solid-state Li+ conductivity of 1.33 × 10-3 S cm-1 was achieved at 200 °C after LiTFSI doping. The high conductivity at the specified temperature remains intact for extended periods of time as a result of the structure's robustness. Furthermore, we demonstrated the first application of a COF electrolyte in an all-solid-state Li battery at 100 °C.

Trimorphism of Zn(NCS)2(4-dimethylaminopyridine)2: Crystal Structures, Thermodynamic Relations, and Comparison with the Co(II) Polymorphs

Reaction of Zn(NCS)2 with 4-dimethylaminopyridine (DMAP) leads to the formation of three polymorphic modifications of Zn(NCS)2(DMAP)2 (I–Zn, II–Zn, and III–Zn), of which only the crystal structure of I–Zn is reported in literature. In all three modifications the Zn(II) cations are tetrahedrally coordinated by two terminal N-bonded thiocyanate anions and two DMAP ligands forming discrete complexes, which differ in the dihedral angle between the DMAP ring planes and the arrangement of the complexes in the crystals. All three modifications show melting, and the thermodynamic relations and the transition behavior were investigated by temperature-dependent X-ray powder diffraction, differential scanning calorimetry, thermomicroscopy, and solvent-mediated conversion experiments. These reveal that I–Zn and II–Zn as well as II–Zn and III–Zn are related by enantiotropism, whereas I–Zn and III–Zn are related by monotropism. The thermodynamic transition temperature between I–Zn and II–Zn is much lower than that betw...

Charge redistribution and the magnetoelastic transition across the first-order magnetic transition in (Mn,Fe) 2 (P,Si,B)

We used temperature dependent high-resolution x-ray powder diffraction and magnetization measurements to investigate structural, magnetic and electronic degrees of freedom across the ferromagnetic magneto-elastic phase transition in Mn1Fe1P0.6-wSi0.4Bw (w = 0, 0.02, 0.04, 0.06, 0.08). The magnetic transition was gradually tuned from a strong first-order (w = 0) towards a second-order magnetic transition by substituting P by B. Increasing the B content leads to a systematic increase in the magnetic transition temperature and a decrease in thermal hysteresis, which completely vanishes for w = 0.08. Furthermore, the largest changes in lattice parameter across the magnetic transition occur for w = 0, which systematically becomes smaller approaching the samples with w = 0.08. Electron density plots show a strong directional preference of the electronic distribution on the Fe site, which indicates the forming of bonds between Fe atoms and Fe and P/Si in the paramagnetic phase. On the other hand, the Mn-site shows no preferred directions resembling the behaviour of a free electron gas. Due to the low B concentrations (w = 0 - 0.08), distortions of the lattice are limited. However, even small amounts of B strongly disturb the overall topology of the electron density across the unit cell. Samples containing B show a strongly reduced variation in the electron density compared to the parent compound without B.

Chromism of Tartrate-Bridged Clamshell-like Platinum(II) Complex: Intramolecular Pt-Pt Interaction-Induced Luminescence Vapochromism and Intermolecular Interactions-Triggered Thermochromism.

A novel luminescent clamshell-like platinum(II) complex with rac-tartrate, rac-[{PtII(4Me2bpy)}2(μ-tart)] (Pt2; 4Me2bpy: 4,4'-dimethyl-2,2'-bipyridine; tartH22-: tartrate), was synthesized, and its vapo-, thermo-, and solvatochromic behavior was studied. The complex was isolated in four crystal forms, namely, Pt2·4H2O (color under ambient light: yellow, λem = 573 nm, intramolecular Pt···Pt separation: 3.55 Å), Pt2·4MeOH (red, 650 nm, 3.33 Å), anhydrate Pt2 (red, no luminescence, 3.70 Å), and Pt2·2H2O (orange, 595 nm, 3.60 Å). Vapo- and heat-responsive crystal-to-crystal phase transitions were observed by time- and/or temperature-dependent powder X-ray diffraction, and the molecular and crystal structures of the above crystal forms were determined by either single-crystal X-ray crystallography or Rietveld refinement of powder X-ray diffraction. Vapor diffusion of MeOH to Pt2·4H2O induced a reversible phase transition to Pt2·4MeOH. This structural transformation significantly changed the intramolecular Pt-Pt interactions, affecting the absorption and emission colors. Accordingly, the luminescence chromism originates from alternation of the luminescent nature between a triplet metal-ligand-to-ligand charge-transfer state (3(MLtart)LbpyCT) of Pt2·4H2O and a triplet metal-metal-to-ligand charge-transfer state (3MMLbpyCT) of Pt2·4MeOH. Heating Pt2·4H2O induced a phase transition to anhydrate Pt2, and under atmospheric conditions, anhydrate Pt2 transformed spontaneously to Pt2·2H2O. Vapor diffusion of H2O to Pt2·2H2O caused reconstruction of Pt2·4H2O. The thermochromism originates from changes in the intermolecular interactions between stacked complexes. The solvatochromism was evaluated using the Kamlet-Taft solvatochromic equation, the acceptor number, and the ET(30) scale for the solvent, and the hydrogen-bond acidity of the solvent contributed significantly to the solvent-dependent absorption properties.

Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

We study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-xAl2 (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, TC. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl2. A clear anomaly in the lattice parameter is observed at ∼30 K for x = 0.5, which nearly coincides with TC = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below TC for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl2, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl2 [111] is the easy magnetization direction.

MgTi(cat)3, a promising precursor for the preparation of Ti–MOFs?

A new Ti(IV) triscatecholate complex was prepared in aqueous conditions. Its crystal structure was solved, and the complex was fully characterized by multiple techniques, including thermogravimetric analysis, temperature dependent powder X-ray diffraction (XRD), as well as NMR and UV–Vis spectroscopies. Thanks to liquid-state NMR, it is shown that such a complex is simultaneously stable enough in water to avoid the hydrolysis of the Ti(IV) ion, while still being able to undergo ligand exchange. Eventually, preliminary experiments suggest that this precursor is suitable for the preparation of new MOFs built up from polycatecholate ligands in aqueous media.

An unprecedented structural phase transition in struvite-type compounds: dimorphism of KMgAsO4(H2O)6

Abstract The crystal structure of struvite-type KMgAsO4(H2O)6 has been redetermined from single crystal X-ray diffraction data at room temperature. The previous structure model based on powder X-ray diffraction data was confirmed with higher precision and accuracy and with all hydrogen atoms located. KMgAsO4(H2O)6 undergoes a reversible phase transition of the continuous type at 263(2) K, changing the symmetry from orthorhombic to monoclinic. The corresponding Pnm21→P1121 symmetry reduction is of a translationengleiche type with index 2 and was monitored by temperature-dependent powder X-ray diffraction measurements. Such a phase transition is unprecedented for struvite-type compounds. The crystal structure of the monoclinic polymorph was determined from a two-domain crystal at 100 K. Except for the motion of one of the water molecules towards stronger hydrogen-bonding interactions, structural changes between the two polymorphs are small.

Wide-Range Columnar and Lamellar Photoluminescent Liquid-Crystalline Lanthanide Complexes with Mesogenic 4-Pyridone Derivatives.

A series of liquid crystals with various lanthanide ions (EuIII , SmIII , and TbIII ) was designed and prepared starting from the corresponding lanthanide nitrates and N-alkylated 4-pyridone derivatives bearing mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl=hexyl, octyl, decyl, dodecyl, tetradecyl, or hexadecyl). These new lanthanidomesogens were investigated for their mesogenic properties by a combination of differential scanning calorimetry, polarizing optical microscopy, and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was assessed by thermogravimetric analysis. All of these complexes show enantiotropic liquid-crystalline behavior with lamellar (SmA) phases in the case of shorter-chain complexes (C6 and C8 ) or hexagonal columnar phases (Colh ) for complexes with longer alkyl chains (C12 , C14 , and C16 ), which were assigned on the basis of their characteristic textures and XRD studies. For complexes with an intermediate number of carbon atoms in the side chains (C10 ), both a lamellar phase at lower temperatures and a Colh phase at higher temperatures were evidenced. In the solid state, all these complexes show characteristic emissions assigned to the corresponding lanthanide ion. In addition, the luminescence decay curves showed single-exponential decays with characteristic times in the millisecond range (0.75-0.90 ms for EuIII , 0.045-0.060 ms for SmIII , and 0.75-1.05 ms for TbIII ).