Variable Temperature XRD Research Articles

Zero thermal expansion in KxMnxIn2-x(MoO4)3 based materials

Zero thermal expansion (ZTE) materials can solve problems such as device failure and cracking caused by mismatched coefficient of thermal expansion. However, ZTE material is rare in nature. NaZr2(PO4)3 is a framework compound with near-zero thermal expansion due to coupled rotations of rigid ZrO6 and PO4 polyhedra in the structure, and several studies have been devoted to obtaining more ZTE compounds by chemical substitution of Na or Zr. Inspired by the AAV concept we proposed, in this work, the PO4 tetrahedra with a small volume has been replaced by the large volume MoO4 tetrahedra in KxMnxIn2-x(MoO4)3 (x = 0.4, 0.6, 0.8, and 1.0) compounds to provide more space for the coupling rotation of the polyhedron, and reduce the coefficient of thermal expansion. On the other hand, the flexibility of the framework structure has been modulated by the content of K+ to achieve new ZTE materials, and the effects of K+ content on crystal structure and thermal expansion have been analyzed in detail by combining variable temperature XRD and Raman. These findings not only provide more ZTE materials, but also suggest a promising design method for ZTE materials.

Synthesis, thermal expansion and optical properties of ZrV2O7 thin films

Cubic ZrV2O7 thin films have been synthesized by sol-gel spin-coating method. The influences of annealing temperatures on the phase composition and morphology of ZrV2O7 thin films were investigated using XRD, SEM, and EDX. Negative thermal expansion (NTE) and optical performances of cubic ZrV2O7 thin films were analyzed using variable temperature XRD and UV–Vis spectroscopy. Results indicate that as-deposited ZrV2O7 thin films have an amorphous structure with smooth and dense surface. Cubic ZrV2O7 thin films were prepared after heat treatment at 720 °C for 1 h. It was found that the thin films contained V2O5 impurity with the Zr: V = 1:2 precursor solution. Pure cubic ZrV2O7 thin films were fabricated with the Zr: V = 1.75:2 precursor solution. Cubic ZrV2O7 thin films show isotropic NTE in the temperature range of 100–700 °C. The coefficients of thermal expansion (CTEs) of ZrV2O7 films along the a, b, and c axes are −6.88 × 10−6 °C−1, and the volumetric and linear CTEs are −20.56 × 10−6 °C−1 and -6.85 × 10−6 °C−1, respectively. The transmittance of cubic ZrV2O7 thin film is approximately 80 %.

Phase evolution, electrical properties, and conductivity mechanism in LiNbWO6

The tetragonal LiNbWO 6 (α−LiNbWO 6 ) with a trirutile structure was previously reported to have good lithium ion conductivity. However, the electrical properties of the hexagonal LiNbWO 6 (β−LiNbWO 6 hereafter) polymorph have not been reported yet mainly due to the difficulty to obtain single-phase. Herein, by quenching the sample from high temperature to room temperature at ambient air condition, a series of pure-phase β−LiNb 1- x Ta x WO 6 ( x = 0, 0.05, 0.1) materials were successfully prepared. The phase evolutions and conductivities of these materials were investigated by variable temperature X-ray diffraction and alternating current impedance spectroscopy techniques, respectively. The results revealed that lithium ion conduction also dominated in this hexagonal polymorph of LiNbWO 6 and an interesting great ionic conduction enhancement behavior was observed at a temperature region of 660-800 ºC due to the minor phase transition from hexagonal to tetragonal. In addition, the possible ionic conducting mechanisms in both the tetragonal and hexagonal LiNbWO 6 materials were studied by the bond-valence-based method for the first time. The results disclosed two-dimensional and three-dimensional lithium ion migration pathways for the tetragonal and hexagonal LiNbWO 6 , respectively. • Hexagonal LiNb 1-x Ta x WO 6 (0≤x≤0.1) was prepared through solid-state reaction. • Lithium ion conduction was identified in hexagonal LiNb 1-x Ta x WO 6 . • Phase evolutions of LiNb 1-x Ta x WO 6 were investigated by variable temperature XRD. • Great conduction increase at 650-800 ºC was due to a composite electrolyte effect. • Conducting mechanisms for both the tetragonal and hexagonal LiNbWO 6 was studied.

Two-dimensional crystallization of cyclopolymers

Free-standing 2D polymer materials with graphene-like crystalline layers hold great promise for many state-of-art applications. However, their fabrication remains challenging. A ferrocene tethered cyclopolymer (pFcMMA) is synthesized via the free radical polymerization of a divinyl monomer in this work. PFcMMA has a high degree of cyclization, but is not a stereo-regular structure like most vinyl polymers synthesized in free radical polymerization. PFcMMA can crystallize on the surface to form 2D crystals, which is evidenced by the birefringence phenomena, DSC and XRD analysis, and microscopic observation. Powder XRD of crystalline pFcMMA shows sharp interlayer diffraction, indicative of a highly crystalline phase. The crystallization process is supposed to follow the nonclassic crystallization pathway, i.e. the orientation of cyclopolymer main chains followed by the conformation transition of the side groups to form 2D crystalline layers. Variable temperature XRD combined with DSC analysis and polarizing optical microscopic observation demonstrate that the 2D crystalline phase begins to transition to a 3D crystalline phase at about 45 °C, the latter has a melting point at about 60 °C. The solid-solid crystalline transition is reversible and without intermediate melting, and the 2D crystalline phase is more stable at room temperature than the 3D phase. It is rationalized that nucleation from solutions is predominantly an entropy-driven process, while interactions between side groups and those between far separated main chains also benefit the formation of 2D crystalline phase. The commonalities of the crystallization processes of cyclopolymers are discussed. • A ferrocene tethered cyclopolymer forms 2D crystals on water surface. • The 2D crystalline phase undergoes a reversible solid-solid transition. • The 2D form appears to be the stable form at room temperature. • Formation of a 3D crystal at higher temperatures is observed. • The 2D crystallization process is entropy driven benefiting from group interactions.

Cs2Bi2Sr(P2O7)(PO4)2:Er3+/Yb3+ phosphors for outstanding thermal enhancement of up-conversion under 980 and 1550 nm laser excitations in the 303 to 723 K range

A serious of Er3+/Yb3+ co-doped Cs2Bi2Sr(P2O7)(PO4)2 (CBSPO) phosphors are prepared by solid phase reaction method, and the related thermal enhancement of up-conversion luminescence (UCL) are studied in depth under 980 and 1550 nm laser excitations. When doping concentration of Er3+is fixed at 0.1, and doping concentration of Yb3+ is adjusted to improve the thermal enhancement effect in the temperature range from 303 to 723 K. The optimal doping concentrations of Er3+/Yb3+ are found as 0.1 and 0.5, and the maximum enhancement of green UCL emission reaches 5.25 and 16.74 times under 980 and 1550 nm laser excitations, respectively. This is because of the combined action of electronic thermal agitation, phonon assisted transition and lattice distortion of doping Er3+ sites. The change of structure with temperature is studied by variable temperature XRD. Additionally, based on FIR technique, the absolute sensitivity of 0.00955 K−1 at 557 K, 0.00643 K−1 at 509 K are got in CBSPO:0.1Er3+/0.3Yb3+ under 980 nm laser excitation and in CBSPO:0.1Er3+/0.4Yb3+ under 1550 nm laser excitation, respectively. The structure changes of polyphosphate with temperature provide new ideas for development of thermally enhanced up-conversion phosphors, which can be applied as optical thermometer at high temperature environment.

Assessing the Importance of Cation Size in the Tetragonal-Cubic Phase Transition in Lithium-Garnet Electrolytes.

Lithium garnets are promising solid-state electrolytes for next-generation lithium-ion batteries. These materials have high ionic conductivity, a wide electrochemical window and stability with Li metal. However, lithium garnets have a maximum limit of seven lithium atoms per formula unit (e.g., La3 Zr2 Li7 O12 ), before the system transitions from a cubic to a tetragonal phase with poor ionic mobility. This arises from full occupation of the Li sites. Hence, the most conductive lithium garnets have Li between 6-6.55 Li per formula unit, which maintains the cubic symmetry and the disordered Li sub-lattice. The tetragonal phase, however, forms the highly conducting cubic phase at higher temperatures, thought to arise from increased cell volume and entropic stabilisation permitting Li disorder. However, little work has been undertaken in understanding the controlling factors of this phase transition, which could enable enhanced dopant strategies to maintain room temperature cubic garnet at higher Li contents. Here, a series of nine tetragonal garnets were synthesised and analysed by variable temperature XRD to understand the dependence of site substitution on the phase transition temperature. Interestingly the octahedral site cation radius was identified as the key parameter for the transition temperature with larger or smaller dopants altering the transition temperature noticeably. A site substitution was, however, found to make little difference irrespective of significant changes to cell volume.

Effect of In or Ge substitution on magnetic ordering in TmGa(In/Ge) compounds

The effect of In or Ge substitution for Ga on magnetic ordering in TmGa(In/Ge) compounds was systematically investigated, where three samples of TmGa, TmGa0.9In0.1 and TmGa0.9Ge0.1 were successfully synthesized. For TmGa, two transitions from ferromagnetic (FM) to antiferromagnetic (AFM) phase at TFA = 12.6 K and from AFM to paramagnetic (PM) phase at TN = 15.6 K were clearly identified. For TmGa0.9In0.1, it shows similar magnetic transitions with TFA = 10.6 K and TN = 14.2 K. For TmGa0.9Ge0.1, Ge substitution plays an effective role on the magnetic ordering, where only one transition from AFM-to-PM occurs and the transition from FM-to-AFM disappears. Variable temperature XRD experiments confirm that the bond length between the nearest neighboring Tm atoms undergoes a sharp change around TFA with increasing temperature. The magnetic ordering and transition in TmGa(In/Ge) compounds can be well explained by lattice distortion based on Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange interactions. Furthermore, In or Ge substitution has a great influence on the magnetocaloric effect as well.

Photo-responsive graphene oxide liquid crystal hybrid modified with imidazolium surfactant containing azobenzene

ABSTRACT A novel photo-responsive imidazolium surfactant containing azobenzene mesogenic cores (CAzoCM) was designed and synthesised to modify graphene oxide, forming imidazolium surfactant-graphene oxide hybrid (CAzoCM-GO), focusing on the correlation between their mesomorphic behaviour, photo-responsive properties and their chemical structure. CAzoCM and CAzoCM-GO were characterised by FT−IR, Raman spectroscopy and XPS, respectively. The results showed that GO was partially reduced by CAzoCM due to the strong electron effect of the imidazole group. The liquid crystal properties of CAzoCM and CAzoCM-GO were investigated by DSC, POM and variable temperature XRD, respectively. CAzoCM exhibited a smectic A phase as well as the rare smectic C phase and the introduction of GO did not destroy the liquid crystal properties of CAzoCM. Furthermore, the photo-responsive behaviour of CAzoCM and CAzoCM-GO had also been studied by UV-vis spectrum. CAzoCM could be switched from trans to cis isomer in 270 s when it was irradiated under ultraviolet light and from cis to trans isomer in 660 s when it was irradiated under visible light. CAzoCM-GO exhibited more sensitive response behaviour, the photo-responsive time from trans to cis isomerisation became 110 s while the photo-responsive time from cis to trans isomerisation became 195 s.

Cascade Dynamics of Multiple Molecular Rotors in a MOF: Benchmark Mobility at a Few Kelvins and Dynamics Control by CO2.

Achieving sophisticated juxtaposition of geared molecular rotors with negligible energy-requirements in solids enables fast yet controllable and correlated rotary motion to construct switches and motors. Our endeavor was to realize multiple rotors operating in a MOF architecture capable of supporting fast motional regimes, even at extremely cold temperatures. Two distinct ligands, 4,4′-bipyridine (bipy) and bicyclo[1.1.1]pentanedicarboxylate (BCP), coordinated to Zn clusters fabricated a pillar-and-layer 3D array of orthogonal rotors. Variable temperature XRD, 2H solid-echo, and 1H T1 relaxation NMR, collected down to a temperature of 2 K revealed the hyperfast mobility of BCP and an unprecedented cascade mechanism modulated by distinct energy barriers starting from values as low as 100 J mol–1 (24 cal mol–1), a real benchmark for complex arrays of rotors. These rotors explored multiple configurations of conrotary and disrotary relationships, switched on and off by thermal energy, a scenario supported by DFT modeling. Furthermore, the collective bipy-ring rotation was concerted with the framework, which underwent controllable swinging between two arrangements in a dynamical structure. A second way to manipulate rotors by external stimuli was the use of CO2, which diffused through the open pores, dramatically changing the global rotation mechanism. Collectively, the intriguing gymnastics of multiple rotors, devised cooperatively and integrated into the same framework, gave the opportunity to engineer hypermobile rotors (107 Hz at 4 K) in machine-like double ligand MOF crystals.

Synthesis and thermal expansion behaviors of spin-coated Sc2Mo3O12 thin films

Orthorhombic Sc2Mo3O12 films have been successfully prepared via spin coating technique followed by annealing at 500–750 °C. The phase composition, microstructure, morphology and negative thermal behavior of the synthesized Sc2Mo3O12 films were investigated. XRD and XPS analysis indicate that as-deposited film is amorphous. Orthorhombic Sc2Mo3O12 films can be prepared after post-annealing at 500–750 °C for 1 h. The crystallinity of Sc2Mo3O12 films gradually improved with the increase of post-annealing temperature. SEM analysis shows as-deposited film is smooth and compact, and the grain size of Sc2Mo3O12 film grows up as the post-annealing temperature increases. Variable temperature XRD analysis demonstrates that the synthesized orthorhombic Sc2Mo3O12 films show stable thermo-chemical and anisotropic NTE property in 25–700 °C. The corresponding coefficients of thermal expansion (CTEs) of the orthorhombic Sc2Mo3O12 film in a, b and c directions are −6.68 × 10−6 °C−1, 5.08 × 10−6 °C−1 and −4.76 × 10−6 °C−1, respectively. The whole unit cell of the orthorhombic Sc2Mo3O12 film shrinks and the volumetric CTE of the Sc2Mo3O12 thin film is −6.36 × 10−6 °C−1, and the linear CTE is about −2.12 × 10−6 °C−1 (αv = 3αl).

Novel cholesterol-based liquid crystalline dimers: the α-cyanostilbene group served as a photofluorophore and mesogenic moiety

ABSTRACT Cyanostilbene units are vigorous candidates for chromophores and mesogens. Therefore, a series of dimer liquid crystals based on cyanostilbene and cholesterol were synthesised and characterised. The structure conforms to the molecular design and its physicochemical properties are stable. With the growth of the inner spacer flexible carbon chain, the mesomorphic properties are greatly different: not only the odd–even effect of the clearing points (/clearing enthalpies) is caused but also the samples exhibit increasingly complex enantiotropic mesophases, including SmC*, SmA and N* phases. Corresponding textures of these phases were observed, such as polygonal textures, focal-conic textures with dechiralisation lines and oily streaks textures, etc., and phase structures were further verified using variable-temperature XRD. Through the combined use of UV and fluorescence emission spectrometers, it was found that the increase of water content caused the enhancement of fluorescence intensities and the redshift of UV absorptions, which confirmed the fascinating aggregation-induced emission enhancement (AIEE) effect of the ChM-CN molecules.

Tunable emission and selective luminescence sensing for nitro- pollutants and metal ions based on bifunctional lanthanide metal-organic frameworks

Series of Eu/Tb bifunctional metal-organic frameworks (MOFs) [EuxTb1-x(L)(H2O)3]n (1-EuxTb1-x) (H4L+·Cl− = 1, 3-bis (3, 5-dicarboxyphenyl) imidazolium chloride) were synthesized successfully by solvothermal reaction. In these complexes, the adjacent Tb3+ or Eu3+ are linked by L3− to form two-dimensional sheet, and then forming three-dimensional framework by various H-bondings. All of complexes have wonderful selectivities and sensitivities for detecting 4-nitrophenol (4-NP) and Fe3+, comparatively speaking, the mixed [Eu0.5Tb0.5(L)(H2O)3]n (1-Eu0.5Tb0.5) has better sensing performance than isolate [Eu(L)(H2O)3]n (1-Eu) or [Tb(L)(H2O)3]n (1-Tb) for 4-NP; while 1-Tb has better sensing performance for Fe3+, the highest quenching constants Ksv for 4-NP and Fe3+ reach to 7.5 × 106 M−1 and 9.6 × 105 M−1. The variable temperature XRD and regenerated experiments prove the good thermal and structural stabilities of 1-EuxTb1-x. Furthermore, the sensing mechanisms of complexes as bifunctional sensors have been explored in detail based on experiments and calculations.

In-Situ Characterization of the Li-Al System at Elevated Temperatures

We will describe our platform for ex- and in-situ characterization of lithium ion electrode and electrolyte materials over a wide range of temperatures, and our use of this platform to characterize phase formation and dissociation in the Li-Al system. Aluminum electrodes have been studied for use in lithium electrochemical cells for more than 40 years. Electrochemical insertion of lithium in to aluminum at very high temperatures (>400 °C) follows the equilibrium phase diagram; studies at e.g. room temperature only demonstrate the formation of LiAl. The formation of the other expected Li-Al phases, Li3Al2 and Li9Al4, is thought to be inhibited by slow diffusion of Li in LiAl. Aluminum is available in a wide variety of morphologies and manufacturing-induced microstructures and as such is a model test platform for deconvoluting the effects of microstructure, diffusion, and phase formation in metal alloy electrodes. Our core enabling technology is an adaptable high-temperature compatible cell design inspired by high-temperature compatible primary cell hardware and adapted from earlier work. Our double-ended glass-to-metal Conflat cells are compatible with low and high voltage electrode materials, adjustable (and commercially-relevant) electrode thicknesses and stack pressures, and can maintain ultra-high vacuum (<10-7 Pa) tight seals at temperatures up to 415 °C. Results from in-situ cycling of a Conflat cell with lithium and aluminum foil electrodes at 110 °C are presented in Fig. 1. Three voltage plateaus are evident, and the step changes between plateaus roughly correspond with the expected phase transition compositions (i.e. LiAl for Li/Al = 0 <–> 1, Li3Al2 for Li/Al = 1 <–> 1.5, Li9Al4 for Li/Al = 1.5 <-> 2.25). XRD patterns collected at room temperature (ex-situ) at three indicated compositions (x1, x2, x3) are also provided in Fig. 1. Patterns collected from samples cycled to 200 mV vs. Li metal on insertion (x1) and 150 mV vs. Li metal on removal (x3) indicate LiAl and Li3Al2 are present, as expected. However, the XRD pattern collected from the sample cycled to 40 mV vs. Li metal on removal (x2) indicates Li1.77Al, rather than Li9Al4, is present at a composition of Li/Al = 2.2. Li9Al4 has been detected in samples cycled in different conditions (temperature, current density, voltage limits, sample morphology etc.) The discrepancy between measured and expected phase composition at x2 (Li/Al = ~2.2 vs. ~1.8, respectively) is attributed to consumption of lithium in solid-electrolyte interphases (SEI). Li3Al2 (at composition x3, Li/Al = 1.8) has a similar discrepancy (expected composition of Li/Al = 1.5). Known phase transitions can therefore be used as guideposts to quantify SEI formation. XRD results shown in Fig. 1 and described above were collected by cooling and then disassembling Conflat cells and incorporating the lithiated electrode in a polypropylene encapsulated sample holder. A major advantage of Conflat cell technology is the ability to bolt-on new functionality without compromising cell performance. Conflat flanges incorporating x-ray transparent windows are now being incorporated in to our cells. We will present ex- and in-situ (variable temperature cycling, room temperature XRD, with and without cell disassembly) and in-operando (integrated variable temperature cycling and XRD, without cooling) results from aluminum thin films and (much thicker, but still thin) aluminum foils to map out phase formation as a function of temperature, sample morphology, and static and dynamic stress. This data, when coupled with insight in to Li diffusion rates and nucleation barriers for the various Li-Al phases, will enable a more complete understanding of ion mobility and phase formation and stability in the Li-Al and other metal alloy systems. Figure 1

Understanding the complex structural features and phase changes in Na2Mg2(SO4)3: A combined single crystal and variable temperature powder diffraction and Raman spectroscopy study

Sodium mixed metal sulphates have attracted considerable attention, both in terms of mineralogy and more recently due to interest in Na ion containing materials for battery applications. The phase, Na2Mg2(SO4)3, has been previously reported to undergo a phase change to langbeinite at high temperatures, which is interesting given that usually the langbeinite structure is only adopted when large alkali metal ions, e.g. K, Cs, are present. Nevertheless the room temperature structure of this phase has remained elusive, and so in this work, we report a detailed structural study of this system. We show that room temperature Na2Mg2(SO4)3 can only be prepared by quenching from high temperature, with slow cooling leading to phase separation to give the previously unreported systems, Na2Mg(SO4)2 and Na2Mg3(SO4)4. We report the structures of quenched Na2Mg2(SO4)3 (monoclinic, P21), as well as Na2Mg(SO4)2 (triclinic, P1̅) and Na2Mg3(SO4)4 (orthorhombic, Pbca), detailing their complex structural features. Furthermore, we report a study of the thermal evolution of quenched Na2Mg2(SO4)3 with temperature through variable temperature XRD and Raman studies, which shows a complex series of phase transitions, highlighting why this phase has proven so elusive to characterise previously, and illustrating the need for detailed characterisation of such sulphate systems.

Competing forces in the self-assembly of amide-functionalized discotic mesogens.

The effect of incorporating a single amide group on the self-assembly of discotic mesogens was examined. Two series of tetraalkoxydibenzophenazines amides were prepared: tertiary diethyl amides, dEt(n) incapable of hydrogen bonding, and secondary amides HBu(n) that can act as both H-bond donors and acceptors. These compounds exhibit markedly different behavior in solution; NMR studies of dEt(n) show no evidence of self-association, whereas HBu(n) strongly associate via H-bonding and π-stacking. Compounds HBu(n) also act as small molecule gelators in a range of solvents, a property not observed for the corresponding tertiary amides. All compounds were found to form Colh liquid crystal phases; variable temperature XRD experiments indicate that each column has a diameter approximately equal to that of a single molecule. A comparison of the phase behavior of HBu(n) and dEt(n) suggests that the columnar phases of the former are stabilized by hydrogen bonding, likely at the expense of local parallel alignment of these molecules. Single crystal X-ray diffraction studies revealed that dEt(6) adopts an antiparallel arrangement in the solid state, in keeping with previous theories of packing within columnar LC phases. These studies highlight the interplay between competing factors, such as hydrogen bonding, π-stacking and dipole-dipole interactions that affect the stability of the LC phases.

Densification and negative thermal expansion property of In0.5Sc1.5(MoO4)3 ceramics

Orthorhombic In0.5Sc1.5(MoO4)3 ceramics with 3 wt% MgO as sintering aid were synthesized via solid state method at various temperatures. The effects of sintering temperature and 3 wt% MgO additive on the microstructure, density and negative thermal expansion property of the In0.5Sc1.5(MoO4)3 ceramics were examined using XRD, SEM and TMA. The results indicate that the increase of twice-sintering temperature promotes densification, and the grain size grows from 1 μm to 7 μm. When the twice-sintering temperature is further raised to 1200 °C, impurity Sc2O3 is detected due to the decomposition of In0.5Sc1.5(MoO4)3. The introduction of MgO as a sintering aid strongly affects the densification and negative thermal expansion stability of the In0.5Sc1.5(MoO4)3 ceramics owing to the formation of the liquid phase MgMoO4. The In0.5Sc1.5(MoO4)3 ceramics with 3 wt% MgO show more stable negative thermal expansion, and their average linear coefficients of thermal expansion (CTEs) are all tested to be between 4 × 10 −6 °C−1 and 5 × 10 −6 °C−1 at 30–700 °C. The variable temperature XRD results reveal In0.5Sc1.5(MoO4)3 shows anisotropic negative thermal expansion. The average CTEs of In0.5Sc1.5(MoO4)3 along a, b and c-axis are calculated to be −4.86 × 10 −6 °C−1, 4.25 × 10 −6 °C−1 and -3.25 × 10 −6 °C−1, respectively, and the volumetric CTE is calculated to be −3.83 × 10 −6 °C−1 at 25–700 °C.

Non‐Perovskite Hybrid Material, Imidazolium Lead Iodide, with Enhanced Stability

AbstractA systematic study of a new hybrid organic‐inorganic material where the cation has been replaced with imidazolium is presented. Imidazolium lead iodide (ImPI) shares the same stoichiometry of ABX3 as a perovskite, however, it has a hexagonal structure. This material shows a vastly improved thermal stability as compared to the more popular hybrid perovskite, methyl ammonium lead iodide (MAPI). ImPI also exhibits a dramatic phase stability as compared to MAPI as demonstrated by the variable temperature XRD data (both low temperature and high temperature). In addition to the enhanced thermal robustness, ImPI shows three times better stability than MAPI under ambient conditions. The stability can be attributed to better packing efficiency of the ImPI lattice which in turn depends on the symmetrical and bulkier organic cation, imidazolium. Optoelectronic measurements were also performed and specifically, unlike for MAPI, photoluminescence measurements of ImPI showcased a broad emission over a range of 500 nm to 900 nm which could be attributed to the presence of self‐trapped excitons and as such this broad emission holds promise for light emitting device applications.

High-temperature dielectric relaxation mechanism in Ba4SmFe0.5Nb9.5O30 tungsten bronze ceramics

The high temperature dielectrics properties of unfilled tungsten bronze ceramics, Ba4SmFe0.5Nb9.5O30, were studied. The temperature dielectric properties and the variable temperature XRD data, in addition to the XPS data indicated that BSFN ceramics have no phase changes from 25 °C to 450 °C; the high temperature relaxation behaviour around 350 °C is closely related to the oxygen defects. Frequency dependence of temperature electrical conductivity relaxation of Ba4SmFe0.5Nb9.5O30 ceramics was well fitted by the Arrhenius relationship with Ea ~ 0.65 eV.

The Anisotropic Thermal Expansion of Non-linear Optical Crystal BaAlBO3F2 Below Room Temperature

Thermal expansion is a crucial factor for the performance of laser devices, since the induced thermal stress by laser irradiation would strongly affect the optical beam quality. For BaAlBO3F2 (BABF), a good non-linear optical (NLO) crystal, due to the highly anisotropic thermal expansion its practical applications are strongly affected by the “tearing” stress with the presence of local overheating area around the laser spot. Recently, the strategy to place the optical crystals in low-temperature environment to alleviate the influence of the thermal effect has been proposed. In order to understand the prospect of BABF for this application, in this work, we investigated its thermal expansion behavior below room temperature. The variable-temperature XRD showed that the ratio of thermal expansion coefficient between along c- and along a(b)- axis is high as 4.5:1 in BABF. The Raman spectrum combined with first-principles phonon analysis revealed that this high thermal expansion anisotropy mainly ascribe to progressive stimulation of the respective vibration phonon modes related with the thermal expansion along a(b)- and c-axis. The good NLO performance in BABF can be kept below room temperature. The work presented in this paper provides an in-depth sight into the thermal expansion behavior in BABF, which, we believe, would has significant implication to the manipulation in atomic scale on the thermal expansion of the materials adopted in strong-field optical facility.

Post‐synthetic Modification of a Dinuclear Spin Crossover Iron(III) Complex

The dinuclear iron(III) complex [Fe(salten)2(bipytz)](BPh4)2·EtOH (1) was synthesized and its post‐synthesis modification yielded [Fe(salten)2(bipydz)](BPh4)2·EtOH (2). The crystal structures and magnetic behaviors of 1 and 2 were investigated by variable temperature XRD, magnetic susceptibility, and Mössbauer spectra measurements, with each of these dinuclear iron(III) complexes exhibiting gradual spin crossover behavior.