Orthorhombic Polymorph Research Articles

Benzilic acid: a monoclinic polymorph

The title compound, C14H12O3, is an α-hydroxycarboxylic acid whose orthorhombic polymorph has been reported earlier [Qiu et al. (2007). Inorg. Chim. Acta, 360, 1819–1824]. The asymmetric unit contains two complete molecules. Classical hydrogen bonds, as well as C—H...O contacts, connect the molecules to infinite chains along the crystallographic c-axis direction.

Defect Structure and Luminescence of κ‐Ga2O3 Micro‐Monocrystals

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material.

Exfoliation of graphite and the discovery of the unique properties of graphene─graphite's single layer─have raised significant attention to layered compounds as potential precursors to 2D materials with applications in optoelectronics, spintronics, sensors, and solar cells. In this work, a new orthorhombic polymorph of yttrium bromide, oC16-YBr3 was synthesized from yttrium and CBr4 in a laser-heated diamond anvil cell at 45 GPa and 3000 K. The structure of oC16-YBr3 was solved and refined using in situ synchrotron single-crystal X-ray diffraction. At high pressure, it can be described as a 3D framework of YBr9 polyhedra, but upon decompression below 15 GPa, the structure motif changes to layered, with layers comprising edge-sharing YBr8 polyhedra weakly bonded by van der Waals interactions. The layered oC16-YBr3 material can be recovered to ambient conditions, and according to Perdew-Burke-Ernzerhof-density functional theory calculations, it exhibits semiconductor properties with a band gap that is highly sensitive to pressure. This polymorph possesses a low exfoliation energy of 0.30 J/m2. Our results expand the list of layered trivalent rare-earth metal halides and provide insights into how high pressure alters their structural motifs and physical properties.

Synergistic Effect of Dual Phases to Improve Lithium Storage Properties of Nb2O5.

Niobium pentoxides (Nb2O5) present great potential as next-generation anode candidates due to exceptional lithium-ion intercalation kinetics, considerably high capacity, and reasonable redox potential. Although four phases of Nb2O5 including hexagonal, orthorhombic, tetragonal, and monoclinic polymorphs show diverse characteristics in electrochemical performance, stable lifetime, high specific capacity, and fast intercalation properties cannot be delivered simultaneously with a single phase. Herein, this issue is addressed by generating a homogeneous mixture of orthorhombic and monoclinic crystals at the nanoscale. Reversible lithium-ion intercalation/deintercalation of the monoclinic phase is achieved, and exceptional lithium storage sites are created at the interface of the two phases. As a result, electrochemical features of stable lifetime from the orthorhombic phase and high specific performance from the monoclinic phase are harmoniously combined. This dual-phase Nb2O5/C nanohybrids deliver as high as 380 mA h g-1 (0.01-3.0 V) and 184 mA h g-1 (1.0-3.0 V) after 200 cycles. The essential principle of property enhancement is further confirmed through in situ XRD measurements and DFT calculations. The dual-phase concept can be further applied on electrodes with multiphases to achieve high electrochemical performance.

Volatile Memristive Devices with Analog Resistance Switching Based on Self-Assembled Squaraine Microtubes as Synaptic Emulators.

In this work, the discovery of volatile memristive devices that exhibit analog resistive switching (RS) and synaptic emulation based on squaraine materials is presented. Specifically, organic microtubes (MTs) based on 2,4-bis[(4-(N,N-diisobutyl)-2-6-hydroxyphenyl]squaraine (SQ) are prepared by evaporation-induced self-assembly (EISA). The MTs are ca. 2 μm in diameter (aspect ratio: 10-130). While powder X-ray diffraction data for MTs identify monoclinic and orthorhombic polymorphs, optical data report the monoclinic phase with energetic disorder. By favorable energetic alignment of the Au work function with the SQ HOMO energy, unipolar (hole-only) symmetric metal-insulator-metal devices are formed by EISA of MT meshes on interdigitated electrodes. The DC I-V characteristics acquired exhibit pinched hysteretic I-V loops, indicative of memristive behavior. Analysis indicates Ohmic transport at low bias with carrier extraction by thermionic emission. At high bias, space-charge-limited conduction in the presence of traps distributed in energy, enhanced by a Poole-Frenkel effect and with carrier extraction by Fowler-Nordheim tunneling, is observed. These data indicate purely electronic conduction. I-V hysteresis attenuates at smaller voltage windows, suggesting that carrier trapping/detrapping underpins the hysteresis. By applying triangular voltage waveforms, device conductance gradually increases sweep-on-sweep, with wait-time-erase or voltage-erase options. Using square waveforms, repeated erase-write-read of multiple distinct conductance states is achieved. Such analog RS behavior is consistent with trap filling/emptying effects. By waveform design, volatile conductance states may also be written so that successive conductance states exhibit identical current levels, indicating forgetting of previously written states and mimicking the forgetting curve. Finally, advanced synaptic functions, i.e., excitatory postsynaptic current, paired-pulse facilitation, pulse-dependent plasticity, and a transition from short- to long-term memory driven by post-tetanic potentiation, are demonstrated.

Valorization of acid mine drainage into potable water and valuable minerals through membrane distillation crystallization

Owing to the rise in population growth and demands for the current living standards, mineral and water resources are depleting at the alarming rate. Also, the mineral–water-energy nexus raises a concern of high-quality water and mineral production at low costs. Membrane distillation crystallization (MDC) has emerged as a promising technology capable of simultaneous water and mineral recovery from wastewater or industrially discharged brines. Herein, the MDC was evaluated for recovery of water and precious minerals from acid mine drainage discharged from the mine tailings. High quality fresh water with 99.9 % salt rejection and permeate flux of 2.32 kg·m−2·h−1 was recovered at 52 °C feed inlet temperature. Also, feed temperatures were varied to determine their impact on mineral crystal morphology, size distribution and growth rate. Predominantly recovered minerals were gypsum, manganese fluoride, potassium iron oxide, nickel oxide hydroxide, sodium sulphate and dihydrogen sulphate. Orthorhombic crystal structure of mineral salts was attained at low feed inlet temperature (34 °C). Higher feed inlet temperatures (i.e. 41° C and 52° C) promoted co-crystallization giving rise to orthorhombic polymorph structures. Narrow crystal size distribution was reported at low water recovery factor (initial growth) for all temperatures. However, the particle size distribution broadened as the recovery factor increased. The crystal sizes ranged from 3.91 ± 0.97 µm to 14.04 ± 3.31. Remarkably, crystal growth rate increased with an increase in feed inlet temperature. These findings open a research direction towards economic recovery of mineral and water to supplement the existing shortages. With a myriad of crystals obtained from the MDC process, an additional operational unit is required to selectively recover high economic minerals.

Insights to the production of SnS-cubic thin films by vacuum thermal evaporation for photovoltaics

Thin films of SnS-CUB with a lattice constant of 11.6 Å, 32 units of SnS per cell and an optical bandgap (E g) of 1.7 eV (direct), are mostly produced by chemical techniques. This cubic polymorph is distinct from its orthorhombic polymorph (SnS-ORT) with an E g of 1.1 eV. This work is on the deposition of SnS-CUB thin films of 100–300 nm in thickness by thermal evaporation at substrate temperatures of 400 °C–475 °C on glass or on a chemically deposited SnS-CUB thin film (100 nm). Under a slow deposition rate (3 nm min−1) from a SnS powder source at 900 °C, the thin film formed on a SnS-CUB film or glass substrate at 450 °C is SnS-CUB. At a substrate temperatures of 200 °C–350 °C, the thin film is of SnS-ORT. A low atomic flux and a higher substrate temperature favor the growth of SnS-CUB thin film. The E g of the SnS-CUB film is nearly 1.7 eV (direct gap), and that of the SnS-CUB film is 1.2 eV (indirect gap). The electrical conductivity (σ) of SnS-CUB and SnS-ORT films are 10–7 and 0.01 Ω–1 cm−1, respectively. A proof-of-concept solar cell of the SnS-CUB thin film showed an open circuit voltage of 0.478 V, compared with 0.283 V for the SnS-ORT solar cell. The insights to the deposition of SnS-CUB and SnS0.45Se0.55-CUB (E g, 1.57 eV; σ, 0.02 Ω−1 cm−1) thin films by vacuum thermal evaporation offer new outlook for their applications.

Downsizing FeNb11O29 anode material through ultrafast solid-state microwave-assisted synthesis for enhanced electrochemical performance

Wadsley-Roth oxide FeNb11O29 powder samples are successfully prepared using a simple, cost-effective, and ultrafast microwave-assisted solid-state synthesis for the first time. While conventional solid-state route in furnace requires hours of high-temperature treatment, both monoclinic and orthorhombic polymorphs of FeNb11O29 were obtained in minutes under microwave heating. Combining such short heat treatment with submicrometric oxide precursors enables to limit particle growth during the synthesis. The electrochemical benchmark clearly shows that FeNb11O29 powder samples obtained rapidly from submicrometric oxide precursors exhibit enhanced cycling performance. For example, the monoclinic polymorph prepared in only 5 min offers a high capacity of 179 mAh g-1 (90 % retention) after 500 cycles at 2 A g-1, approximately 20 % more than with conventional synthesis protocol. Electrochemical analysis demonstrates that the extra capacity is gained at low voltage and is probably induced by an easier ionic diffusion occurring in smaller particles. This work confirms the interest of solid-state microwave heating to design of electrode materials with limited particle growth and better cycling performance.

Hypervalent hydridosilicate in the Na-Si-H system.

Hydrogenation reactions at gigapascal pressures can yield hydrogen-rich materials with properties relating to superconductivity, ion conductivity, and hydrogen storage. Here, we investigated the ternary Na-Si-H system by computational structure prediction and in situ synchrotron diffraction studies of reaction mixtures NaH-Si-H2 at 5-10GPa. Structure prediction indicated the existence of various hypervalent hydridosilicate phases with compositions NamSiH(4+m) (m = 1-3) at comparatively low pressures, 0-20GPa. These ternary Na-Si-H phases share, as a common structural feature, octahedral SiH6 2- complexes which are condensed into chains for m = 1 and occur as isolated species for m = 2, 3. In situ studies demonstrated the formation of the double salt Na3[SiH6]H (Na3SiH7, m = 3) containing both octahedral SiH6 2- moieties and hydridic H-. Upon formation at elevated temperatures (>500°C), Na3SiH7 attains a tetragonal structure (P4/mbm, Z = 2) which, during cooling, transforms to an orthorhombic polymorph (Pbam, Z = 4). Upon decompression, Pbam-Na3SiH7 was retained to approx. 4.5GPa, below which a further transition into a yet unknown polymorph occurred. Na3SiH7 is a new representative of yet elusive hydridosilicate compounds. Its double salt nature and polymorphism are strongly reminiscent of fluorosilicates and germanates.

Structural insight into the cooperativity of spin crossover compounds.

Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia)2(NCS)2 (PM = N-2'-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π-π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter-Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.

Polymorphism and up-conversion photoluminescence properties of Y2WO6 doped with Yb3+/Er3+ under excitation at 975 nm

This article reports the synthesis and luminescent properties (up-conversion and down-shifting) of the tetragonal and orthorhombic polymorphs of Y2WO6 doped with Erbium (Er3+) and Ytterbium (Yb3+) cations. The syntheses were carried out by a high temperature solid state reaction. The orthorhombic phase was prepared by pressing the parent compounds into pellets of 13 mm diameter. The samples were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Luminescence up-conversion measurements were analyzed using a tunable continuous wave (CW) Ti:sapphire laser system tuned at 975 nm. The results show that the green up-conversion emission is more intense than the red one in both polymorphs. To gain further clarity on this matter, we have also conducted a study on down-shifting emission spectra measured at 378 nm, where only the strong green emission is observed. The pump power dependence and the decay curves of the (4S3/2 → 4I15/2) transition were also evaluated.

Carbonates of alkaline earth metals: Impact of the cation size on strengths of interionic interactions and polymorphic preferences

The energies of all types of pair-wise interionic interactions between atoms of the representative (MCO3)13 clusters sampled from X-ray structures of rhombohedral magnesite (M = Mg) and calcite (M = Ca), on one hand, and orthorhombic aragonite (M = Ca) and cerussite (M = Pb), on the other hand, are evaluated theoretically to ascertain how the size of a divalent metal cation governs the preferable existence of rhombohedral or (and) orthorhombic polymorph (polymorphs) at ambient temperature and pressure. The carbonates studied and their clusters are considered as those consisting of (i) columns of carbonate anions (CAs) separated by trios of cations, (ii) ribbons and layers of CAs, and (iii) rods and layers of cations. For each cluster, coordination energies of six CAs by a cation and six cations by a CA are evaluated. Energies of interactions of C and O atoms of columns and ribbons with cations and energies of inter-anionic C···O, O···O, and C···C interactions in column and ribbons of clusters are compared. Strengths of cation – cation repulsions are also evaluated. Analyses of the interaction energies, interionic distances in the carbonates studied, and thermodynamic properties of carbonates of alkaline earth metals allow one to understand how the size of a particular divalent metal cation affects relative thermodynamic stabilities and the very existence of its rhombohedral or (and) orthorhombic crystalline phase (phases).

The Effect of Y Doping on Monoclinic, Orthorhombic, and Cubic Polymorphs of HfO2: A First Principles Study

The Effect of Y Doping on Monoclinic, Orthorhombic, and Cubic Polymorphs of HfO2: A First Principles Study

Synthesis, Crystal Structure, Hirshfeld Surfaces Analysis, Interaction with DNA and Comparation of Different Bases in Hirshfeld Atom Refinement of New Polymorph of Chlorido(η6-p-cymene)(diclofenac)Ruthenium(II) Organometallic Compound

A new polymorph of the ruthenium(II) diclofenac complex with formula [Ru(p-cymene)(diclo)Cl] was synthesized, and its crystal structure was solved by single crystal X-ray diffraction. The structure was refined by HAR, using five different relativistic bases sets (x2c-SVP, jorge-DZP-DKH, jorge-TZP-DKH, x2c-TZVP, and x2c-TZVPP) and three effective core potential basis sets (ECP-def2-SVP, ECP-def2-TZVP, and ECP-def2-TZVPP). Their influence on the structure parameters was compared. The analysis of the supramolecular structure of the HAR/non-HAR structures, as well as of the orthorhombic polymorph, was supported by the calculation and analysis of the Hirshfeld surfaces. The best results were observed for HAR using triple-zeta-based sets. No significant effect of base choice on Hirshfeld surfaces was observed. A study of the ability of the complex to interact with ct-DNA was also performed. The complex was shown to interact with ct-DNA, but the mode of interaction is not fully elucidated.

Kilogram scale synthesis of C3A polymorphs and their hydration reactions

Studies on the properties of pure C3A phases are often limited to methods requiring small sample amounts due to the lack of a convenient laboratory synthesis yielding sample amounts exceeding 100 g. Here, we report a simple and large scale lab method for the synthesis of C3A polymorphs with yields of up to 500 g per batch. Commercial calcium aluminate cement (CAC) was used to prepare cylindrical green bodies of CaCO3 and Al2O3 (and NaNO3 for orthorhombic and monoclinic polymorphs). The green bodies were sintered at 1300 °C and 1400 °C respectively. The chemical and mineralogical compositions of the obtained C3A polymorphs were analyzed by X-ray powder diffraction and X-ray fluorescence spectroscopy. The reactivities of these C3A polymorphs were compared to conventionally synthesized C3A (using mechanical powder compaction prior to sintering) via in-situ isothermal heat flow calorimetry. Additionally, we demonstrate that synthetic C3A retains its reactivity over one year if stored appropriately. As the new synthesis protocol yields hundreds of grams of C3A, it enables experimental methods such as slump flow testing with pure phases, which is also reported for all polymorphs.

Two Crystal Forms of 4′-Methyl-2,4-dinitrodiphenylamine: Polymorphism Governed by Conformational Flexibility of a Supramolecular Synthon

Single crystals of two polymorphic forms of 4′-methyl-2,4-dinitrodiphenylamine were obtained by crystallization and characterized by X-ray diffraction analysis. One of the forms is non-centrosymmetric (space group P21212), while the second is centrosymmetric (space group P¯1) and contains two crystallographically independent molecules in the asymmetric unit. In both forms, the same supramolecular synthon, a dimer linked by bonding N-H···O, O···O, and C-H···O interactions were found. Despite nearly the same connectivity of the bonding interactions, the conformation of the supramolecular synthon is different, including its unavoidably different symmetry in two polymorphs. The comparison of the crystal packing of the orthorhombic polymorph with that of the related 2,4-dinitrodiphenylamine (space group P21/n) shows the quasi-isostructurality of the fragments, infinite π-stacks joined by weak non-directional intermolecular interactions. However, the fragments are linked by the supramolecular synthons via either a two-fold axis or an inversion center, which lead to only the partial isostructurality of the crystals.

High-Pressure X-ray Diffraction Study of Orthorhombic Ca2Zr5Ti2O16.

The orthorhombic polymorph of Ca2Zr5Ti2O16 (space group Pbca) has been studied by powder X-ray diffraction under high pressures up to 30 GPa using synchrotron radiation. We have found evidence of a structural phase transition at 12-13 GPa. The phase transition causes an enhancement of the crystal symmetry. The high-pressure phase is tetragonal, being described by space group I41/acd. The space groups of the high- and low-pressure phases have a group/subgroup relationship. However, the phase transition is accompanied by a discontinuous change in the unit-cell volume, indicating that the phase transition can be classified as first order. We have also performed density functional theory calculations. These simulations support the occurrence of the orthorhombic-to-tetragonal transition. The pressure-volume equation of state and axial compressibilities have been determined for both polymorphs. The results are compared with previous studies in related oxides.

The Effect of Y Doping on Monoclinic, Orthorhombic, and Cubic Polymorphs of HfO2: A First Principles Study

HfO2 can assume different crystalline structures, such as monoclinic, orthorhombic, and cubic polymorphs, each one characterized by unical properties. The peculiarities of this material are also strongly related to the presence of doping elements in the unit cell. Thus, the present paper has the main purpose of studying and comparing twelve different systems characterized by diverse polymorphs and doping percentages. In particular, three different crystalline structures were considered: the monoclinic P21/c, the orthorhombic Pca21, and the cubic Fm3¯m phases of HfO2. Each one has been studied by using Y as a doping agent with three different contents: 0% Y:HfO2, 8% Y:HfO2, 12% Y:HfO2, and 16% Y:HfO2. For all the systems, density functional theory (DFT) methods based on PBE/GGA, and on the HSE hybrid functionals were used to optimize the geometry as well as to study their optical properties. Depending on the polymorphs, Y affects the formation energy in different ways and causes changes in the optical properties. When the percentage of Y did not exceed 12%, a stabilization of the cubic phase fraction and an increase of the dielectric constant was observed. Additionally, the calculated optical bandgap energies and the refractive index are examined to provide an overview of the systems and are compared with experimental data. The bandgaps obtained are in perfect agreement with the experimental values and show a slight increase as the doping percentage grows, while only minor differences are found between the three polymorphs in terms of both refractive index and optical band gap. The adopted first principles study generates a reasonable prediction of the physical-chemical properties of all the systems, thus identifying the effects of doping phenomena.

Synthesis and Crystal Structure of a New Orthorhombic Polytype of Potassium Ferricyanide

AbstractA new four‐layer orthorhombic polytype of potassium ferricyanide, K3Fe(CN)6, has been determined by single‐crystal X‐ray diffraction supported by powder X‐ray diffraction measurements. It crystallizes in the space group Pbcn with lattice parameters a = 10.3922(7) Å, b = 8.3508(5) Å, c = 26.838(2) Å and Z = 8, indicating a doubled orthorhombic cell along the c direction compared with the previously reported two‐layer orthorhombic polymorph. The structural relationship between these two forms is then discussed with the support of DFT calculations.

From Amorphous to Polycrystalline Rubrene: Charge Transport in Organic Semiconductors Paralleled with Silicon

AbstractWhile progress has been made in the design of organic semiconductors (OSCs) with improved transport properties, the understanding of the mechanisms involved is still limited, hindering further development. In this study, the interplay between structural order and transport considering one single OSC, analogous to past research on silicon is investigated. Rubrene (C42H28) is selected as it spans transport mechanisms from thermally activated hopping in its amorphous form to band‐like in highly ordered crystals in the orthorhombic polymorph. Transport characterizations including variable temperature conductivity, advanced Hall effect, and magnetoresistance measurements are performed on rubrene films with varying levels of order (polycrystalline vs amorphous), crystal phase (orthorhombic vs triclinic), and morphologies (platelet‐like vs spherulitic grains). A conductivity tuning range over four orders of magnitude between polycrystalline (platelet‐like) orthorhombic and amorphous films is reported. As observed in silicon, transport in polycrystalline orthorhombic rubrene is limited by energy barriers at grain boundaries. Additionally, a gradual transition from predominantly band‐like to predominantly hopping transport with increasing disorder, reminiscent of observations in silicon is shown. Nevertheless, OSCs differ from covalently bonded silicon by their weak intermolecular interaction. This study highlights that molecular packing must be optimized in OSCs to favor advantageous π‐orbital overlap and optimized transport properties.