Trigonal Phase Research Articles

Transport properties and electronic phase transitions in two-dimensional tellurium at high pressure

Utilizing in situ Raman spectroscopy, resistivity, and Hall-effect measurements, we conducted an extensive investigation on the continuous electronic phase transitions and transport properties of two-dimensional (2D) tellurium (Te) under high pressure at room and low temperature (80–300 K). The distinguishable decrease in the A1 Raman mode's full width at half maximum in the trigonal phase (Te-I) indicated an electronic phase transition at 2.2 GPa. The following Hall-effect experiments located the Lifshitz transition and the semiconductor-semimetal transition at 0.9 and 1.9 GPa, respectively, and the semiconductor-semimetal transition was also confirmed by resistivity variation through temperature. The charge carrier types of the Te changed from hole to electron during the phase transition from Te-I to Te-II (triclinic phase) at low temperature, while the transport parameters remained almost unchanged during the phase transition from Te-II to Te-III (monoclinic phase). The results offered complete and thorough electronic phase transitions and transport characteristics of 2D Te, hence great advancing the potential application of Te in electronic devices.

Temperature-dependent failure of atomically thin MoTe2.

In this study, we investigated the mechanical responses of molybdenum ditelluride (MoTe2) using molecular dynamics (MD) simulations. Our key focus was on the tensile behavior of MoTe2 with trigonal prismatic phase (2H-MoTe2) which was investigated under uniaxial tensile stress for both armchair and zigzag directions. Crack formation and propagation were examined to understand the fracture behavior of such material for varying temperatures. Additionally, the study also assesses the impact of temperature on Young's modulus and fracture stress-strain of a monolayer of 2H-MoTe2. The investigation was done using molecular dynamics (MD) simulations using Stillinger-Weber (SW) potentials. The tensile behavior was simulated for temperature for 10K and then from 100 to 600K with a 100-K interval. The crack propagation and formation of 10K and 300K 2H-MoTe2 for both directions at different strain rates was analyzed using Ovito visualizer. All the simulations were conducted using a strain rate of 10-4ps-1. The results show that the fracture strength of 2H-MoTe2 in the armchair and zigzag direction at 10K is 16.33 GPa (11.43 N/m) and 13.71429 GPa (9.46 N/m) under a 24% and 18% fracture strain, respectively. The fracture strength of 2H-MoTe2 in the armchair and zigzag direction at 600K is 10.81 GPa (7.56 N/m) and 10.13 GPa (7.09 N/m) under a 12.5% and 12.47% fracture strain, respectively.

Thickness‐Dependent Bandgap and Atomic Structure in Elemental Tellurium Films

Elemental tellurium electrical switch, relying on a transient crystal–liquid–crystal phase transition, has recently been proposed as a promising selector candidate for the next‐generation 3D high‐density memory, bridging performance gap in today's computer. Further miniaturization of the switch cell to increase memory density strongly depends on the scalability of the tellurium film, which, however, has not been experimentally studied. Herein, the tellurium films are prepared with the thickness downscaled from 400 to 2 nm and a significant increase is found in the bandgap from 0.29 to 0.91 eV, as predicted by ab initio molecular dynamics. Interestingly, the as‐deposited tellurium films with a thickness above 3 nm are in the crystalline trigonal phase, whereas 2 nm thick film suddenly becomes amorphous, observed by both Raman and transmission electron microscopies. In this finding, since the leakage current of the elemental tellurium switch is determined by both the Schottky barrier between tellurium/electrode interface and the bandgap of the tellurium film, a reduction in leakage current is predicted with further miniaturization.

Preparation and photoluminescence study of rare-earth-free red emitting La3Ga5SiO14:Mn4+phosphors

Given the growing interest in eco-friendly lighting solutions, the use of high-quality phosphors has become integral to the advancement of all-solid white light-emitting diodes (WLEDs). One novel phosphor, La3Ga5SiO[Formula: see text]:Mn[Formula: see text] (LGS), has been successfully synthesized via a high-temperature solid-state reaction. The crystal structure of LGS is classified as belonging to the trigonal phase, with a space group P321. The excitation spectrum exhibits a wide peak within the wavelength range of 280–440 nm. It emits a highly intense red light, with a peak emission occurring at 715 nm within the spectral range of 670–740 nm is attributed to the transition of Mn[Formula: see text] from 4A[Formula: see text] to 4T[Formula: see text] LGS:Mn[Formula: see text] demonstrates a favorable quantum efficiency of 16% when doped with a concentration of 0.25 mol% Mn. The decay curve of LGS:Mn[Formula: see text] exhibits a pattern of decreasing lifetime as the dopant concentration increases. Additionally, the LGS:Mn[Formula: see text] products demonstrate a CIE chromaticity of (0.688, 0.2644), which is located within the deep red light region. All the aforementioned findings support the potential application of LGS:Mn[Formula: see text] specimens in WLEDs, thereby contributing to the progress of environmentally friendly and energy-efficient lighting.

Effect of the roughness on the photoinduced growth of crystalline tellurium on MoTe2 matrix

In this work, a series of 5 nm thick films of molybdenum oxide (MoO3) were synthesized on SiO2/Si substrates by magnetron sputtering of molybdenum in low vacuum conditions. We used closed-space sublimation (CSS) to tellurize the Mo oxide and to produce pure-phase 1 T′-MoTe2 films by controlling the temperature inside the CSS reactor. Surface analyses showed that tellurium spreads over the surface of the as-grown films, forming localized crystalline precipitates whose distribution depends on the tellularization time. From Raman spectroscopy investigations, we observed that the exposure of these films to visible light leads to a growth of a highly-ordered trigonal phase of tellurium. The intensity evolution of the vibrational modes related to the crystalline phase of tellurium allows us to perform a quantitative analysis of the crystallization. Our results indicate that this process is consistent with the Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the overall crystallization process. By the characteristic growth exponent, we introduce a more specific model which takes into account the diffusion and the dissociation of tellurium chains, which is used to probe how the effective growth rate is affected by the roughness of the samples.

Sliding-mediated ferroelectric phase transition in CuInP2S6 under pressure

Interlayer stacking order has recently emerged as a unique degree of freedom to control crystal symmetry and physical properties in two-dimensional van der Waals (vdW) materials and heterostructures. By tuning the layer stacking pattern, symmetry-breaking and electric polarization can be created in otherwise non-polar crystals, whose polarization reversal depends on the interlayer sliding motion. Herein, we demonstrate that in a vdW layered ferroelectric, its existing polarization is closely coupled to the interlayer sliding driven by hydrostatic pressure. Through combined structural, electrical, vibrational characterizations, and theoretical calculations, we clearly map out the structural evolution of CuInP2S6 under pressure. A tendency toward a high polarization state is observed in the low-pressure region, followed by an interlayer-sliding-mediated phase transition from a monoclinic to a trigonal phase. Along the transformation pathway, the displacive-instable Cu ion serves as a pivot point that regulates the interlayer interaction in response to external pressure. The rich phase diagram of CuInP2S6, which is enabled by stacking orders, sheds light on the physics of vdW ferroelectricity and opens an alternative route to tailoring long-range order in vdW layered crystals.

Optimizing solid electrolytes with 3d transition metal doped Li3YCl6 for Li-ion batteries

Li3YCl6 is a promising candidate for solid electrolytes (SEs) in all-solid-state Li-ion batteries due to its high ionic conductivity, electrochemical stability, and compatibility with metal-oxide electrodes. The monoclinic and trigonal crystal structures of Li3YCl6 with space groups C2/c and P-3m1 have been studied extensively, while little attention has been given to the trigonal P-3c1 phase (space group no. 165). Additionally, Li-ion diffusion mechanism in 3d transition metal (TM) substituted compounds along with their structural stability are interesting to study. Therefore, we investigate the Li diffusion mechanism in Li3YCl6 and TM substituted Li3YCl6 in the P-3c1 phase using first-principles calculations. We have found that all the substituted compounds are thermodynamically stable at room temperature and show high oxidation stability. Li3Y0.875Co0.125Cl6 exhibits the lowest activation energy (0.11 eV) for Li-ion diffusion and the highest Li-ion mobility (σ = 0.39 mS cm−1 at room temperature), which is strongly anisotropic. We used the Crystal Orbital Hamilton Population method to analyze the bonding characteristics of Li3YCl6 and 3d TM substituted Li3YCl6 and found that the Co–Cl bond is weaker than the Cr–Cl bond. This may explain the lower activation energy observed for Li3Y0.875Co0.125Cl6. Our results provide insights into the substitution effect in Li3YCl6 superionic conductors, which could guide the design and development of high-performance SEs for Li-ion batteries.

An ab initio study of electronic, mechanical, and piezoelectric properties of the trigonal, tetragonal and cubic phases of lead-free perovskite SnBO3 (B = Ti, Zr, Hf)

This study offers a comprehensive ab initio analysis of the structural, electronic, and mechanical properties of the trigonal (R3̅), tetragonal (P4mm) and cubic (Pm3̅m) phases of SnBO3 (BTi, Zr, Hf) oxide perovskite compounds using various functionals namely GGA-PBE, PBE0, HSE06, and B3LYP. From formation energy calculation, trigonal symmetry has been found to be the most stable phase. In the structure optimization, B3LYP estimates the largest volume under trigonal and tetragonal symmetry. However, for the cubic system of SnBO3, SnTiO3 possess the largest volume when using PBE-GGA, while B3LYP estimates the largest in SnZrO3 and both PBE-GGA and B3LYP estimates the same magnitude in SnHfO3. When Ti atom is replaced with either Zr or Hf, a notable shift in the second oxygen atomic coordinate was observed in the tetragonal phase along the z-direction, which impacts the lattice parameters leading to an expansion along the a-axis but with contraction along the c-axis. Structural changes have been found to correspond with electronic transitions. While the electronic transition in SnTiO3 takes place along X→Γ, the transitions in both SnZrO3 and SnHfO3 occurs along X→Z in k space. In the cubic system, SnTiO3 showed an indirect X→Z transition, whereas SnZrO3 and SnHfO3 demonstrated a direct X→X transition. Density of states calculations have revealed that contribution from the B-site atom in the energy states around the conduction band edge is reduced as Ti atom is substituted with Zr atom and subsequently with Hf atom for all the crystal phases. Mechanical stability was consistent across all the compounds in all the calculations with various exchange-correlation functionals considered. Analysis of the mechanical parameters of the trigonal phase of SnBO3 has deduced that only SnTiO3 using hybrid functionals shows brittleness. While only SnHfO3 consistently exhibited a ductile nature throughout the functionals considered in the tetragonal phase, all compounds in the cubic phase were ductile. Interestingly, while the bulk modulus increased sequentially from Ti to Zr and then to Hf when B site atom is substituted in tetragonal structures, SnTiO3 emerged as the most robust system in the cubic phase. In the tetragonal system, when Ti atom in SnBO3 is replaced with either Zr or Hf, the piezoelectric response exhibits massive increase associated with the change in atomic position of the second oxygen atom along the c-axis and the response is also predicted to be highest in SnHfO3.

Unlocking the key role of bentonite fungal isolates in tellurium and selenium bioremediation and biorecovery: Implications in the safety of radioactive waste disposal

Research on eco-friendly bioremediation strategies for mitigating the environmental impact of toxic metals has gained attention in the last years. Among all promising solutions, bentonite clays, to be used as artificial barriers to isolate radioactive wastes within the deep geological repository (DGR) concept, have emerged as effective reservoir of microorganisms with remarkable bioremediation potential. The present study aims to investigate the impact of bentonite fungi in the speciation and mobility of selenium (Se) and tellurium (Te), as natural analogues 79Se and 132Te present in radioactive waste, to screen for those strains with bioremediation potential within the context of DGR. For this purpose, a multidisciplinary approach combining microbiology, biochemistry, and microscopy was performed. Notably, Aspergillus sp. 3A demonstrated a high tolerance to Te(IV) and Se(IV), as evidenced by minimal inhibitory concentrations of >16 and >32 mM, respectively, along with high tolerance indexes. The high metalloid tolerance of Aspergillus sp. 3A is mediated by its capability to reduce these mobile and toxic elements to their elemental less soluble forms [Te(0) and Se(0)], forming nanostructures of various morphologies. Advanced electron microscopy techniques revealed intracellular Te(0) manifesting as amorphous needle-like nanoparticles and extracellular Te(0) forming substantial microspheres and irregular accumulations, characterized by a trigonal crystalline phase. Similarly, Se(0) exhibited a diverse array of morphologies, including hexagonal, irregular, and needle-shaped structures, accompanied by a monoclinic crystalline phase. The formation of less mobile Te(0) and Se(0) nanostructures through novel and environmentally friendly processes by Aspergillus sp. 3A suggests it would be an excellent candidate for bioremediation in contaminated environments, such as the vicinity of deep geological repositories. It moreover holds immense potential for the recovery and synthesis of Te and Se nanostructures for use in numerous biotechnological and biomedical applications.

Sampling the Materials Space for Conventional Superconducting Compounds.

A large scale study of conventional superconducting materials using a machine-learning accelerated high-throughput workflow is performed, starting by creating a comprehensive dataset of around 7000 electron-phonon calculations performed with reasonable convergence parameters. This dataset is then used to train a robust machine learning model capable of predicting the electron-phonon and superconducting properties based on structural, compositional, and electronic ground-state properties. Using this machine, the transition temperatures (Tc ) of approximately 200000 metallic compounds are evaluated, all of which are on the convex hull of thermodynamic stability (or close to it) to maximize the probability of synthesizability. Compounds predicted to have Tc values exceeding 5K are further validated using density-functional perturbation theory. As a result, 541 compounds with Tc values surpassing 10K, encompassing a variety of crystal structures and chemical compositions, are identified. This work is complemented with a detailed examination of several interesting materials, including nitrides, hydrides, and intermetallic compounds. Particularly noteworthy is LiMoN2 , which is predicted to be superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38K. LiMoN2 has previously been synthesized in this phase, further heightening its potential for practicalapplications.

Structural, electrochemical, biological, and mechanical assessment of functionally graded Cr-based multilayers for enhanced metal-ceramic bond strength in dental restorations

The failures of metal-ceramic dental restorations happen due to the initiation of a corrosive process that leads to the deterioration of restorations from a mechanical and aesthetic point of view, by releasing ions and corrosion products, causing patient hypersensitivity, as well as by detaching the ceramic from the metal support. The purpose of this study was to improve the metal-ceramic adhesion of dental prosthetic frameworks by covering their metallic components with biocompatible inorganic coatings, resistant to corrosion in the oral cavity environment. Different coating architectures based on chromium oxynitrides were obtained by cathodic arc method on CoCr alloy substrate. GDOES results confirmed the proposed configuration of the multilayers, and (O + N)/(Cr + Si) ratio calculated for each component layer (ranging from 0.7 to 2.7) emphasized the gradual transition from a metallic character towards a ceramic character of the CrSiON outer layer. XRD analysis proved the stability of the coating structure when a ceramic sintering treatment was applied, the Cr2O3 trigonal phases formed as a result of heat treatment, having a beneficial effect on the metal-ceramic bond strength. After 12h immersion in artificial saliva (pH = 5), an increased protection efficiency was observed for all the proposed multilayers. Among them, the best behaviour was exhibited by CrSiN/CrSiON coating, as pointed out by electrochemical impedance spectroscopy. Even after 72h of immersion, the mentioned design proved the highest pore resistance, result ascribed to a more defect free structure, which acted as a corrosion barrier to the electrolyte ingress. However, biological assessment revealed that the best proliferating and metabolic support for human gingival fibroblasts was showed by Cr/CrSi/CrSiN/CrSiON coating. Similar results were obtained by mechanical characterization of the new CoCr-multilayers-ceramic systems (tests performed based on the requirements specified in ISO 9693:2012 standard), indicating that the coating with the highest number of interfaces had also the highest surface roughness and lower contact angles, and therefore, the best bond strength value.

Design and Synthesis of Cubic K3-2 x Bax SbSe4 Solid Electrolytes for K-O2 Batteries.

Developing K-ion conducting solid-state electrolytes (SSEs) plays a critical role in the safe implementation of potassium batteries. In this work, a chalcogenide-based potassium ion SSE is reported, K3 SbSe4 , which adopts a trigonal structure at room temperature. Single-crystal structural analysis reveals a trigonal-to-cubic phase transition at the low temperature of 50 °C, which is the lowest among similar compounds and thus provides easy access to the cubic phase. The substitution of barium for potassium in K3 SbSe4 leads to the creation of potassium vacancies, expansion of lattice parameters, and a transformation from a trigonal phase to a cubic phase. As a result, the maximum conductivity of K3-2 x Bax SbSe4 reaches around 0.1 mS cm-1 at 40 °C for K2.2 Ba0.4 SbSe4 , which is over two orders of magnitude higher than that of undoped K3 SbSe4 . This novel SSE is successfully employed in a K-O2 battery operating at room temperature where a polymer-laminated K2.2 Ba0.4 SbSe4 pellet serves as a separator between the oxygen cathode and the potassium metal anode. Effective protection of the K metal anode against corrosion caused by O2 is demonstrated.

Mechanistic Insight into the Defect-Engineered White Light Emission from the Single-Phase Orthovanadate Phosphor Synthesized by a Facile Rapid Microwave-Assisted Synthesis.

The synthesis of single-phase barium orthovanadate phosphors by a one-pot microwave-assisted hydrothermal approach has been reported, wherein the homogeneous thermal zone generated at the molecular level by microwave radiation gives rise to tunable distortion in the tetrahedral VO4-3 and oxygen vacancies, eventually enabling intrinsic white light emission with CIE of 0.31,0.38, high photoluminescence internal quantum efficiency of 35%, and external quantum efficiency of 28% whereas phosphor synthesized by the hydrothermal route exhibits only bluish-green emission (PLQE: 0.5%). The Rietveld refinement confirms the formation of a single trigonal phase having dissimilar V-O bond lengths and bond angles, implying the formation of a distorted phosphor under optimized conditions, and corroborates with Raman and Fourier transform infrared analyses. The X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis reveal that the origin of white light emission is due to short- and long-range defects, in particular the oxygen vacancies, which eventually form an intermediate energy level in the forbidden region between the valence and conduction bands. Lifetime spectra show triexponential fitting, corresponding to two charge transfer blue and green emission bands (3T2, 3T1 to 1A1) and one oxygen vacancy-related red emission at RT. Furthermore, these phosphors are thermally stable, as no change in the structure or emission characteristics are observed. A prototype fabricated using a 365 nm chip exhibits white-light-emission CIE of 0.353,0.392, correlated color temperature of 4867 K, color rendering index of 85, and high luminous efficacy of 102 lm/W at 140 mA operating current, portentous for practical applications.

Photoluminescence and Raman study of the high-pressure behavior of monoclinic (Eu1-xYbx)2O3 solid solution

The high-pressure behavior of (Eu1-xYbx)2O3 solid solution with Yb3+ content (x) between 0 and 0.2 and monoclinic (B-type) crystalline structure has been studied by means of Raman and photoluminescence spectroscopies up to 15 GPa. A reversible phase transition from the monoclinic (B) to trigonal (A) phase has been observed for all compositions by Raman, with the transition pressure linearly increasing with x. The same conclusion was reached using the Eu3+ photoluminescence as a local probe. The fraction of B and A phases as a function of pressure has been estimated through the integrated intensity of the Eu3+ 5D0-7F0 electronic transition. The possibility of using the evolution of the spectral distribution of the 5D0-7F2 transition to estimate the fraction of each phase with pressure has been also discussed. Moreover, the spectral shifts of the 5D0-7F0 and 5D0-7F1 transitions with pressure have been used to evaluate the effect of pressure on the spin-orbit coupling constant ξ4f.

Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3

NiPSe3 is regarded as a bandwidth-controlled Mott insulator, distinct from the widely studied Mott insulating magnetic graphene MPSe3 (M = Mn and Fe) family. By employing high-pressure synchrotron X-ray diffraction, we observe two structural transitions as a function of pressure. With the help of first-principles calculations, we discover the antiferromagnetic (AFM) moment directions of NiPSe3 switch from out-of-plane to in-plane and the honeycomb layers slide relative to each other at the first structural transition. The in-plane AFM order persists until the second structural transition, whereupon the two-dimensional (2D) structure assumes a more three-dimensional (3D) character. A bandwidth-controlled Mott insulator-metal transition (IMT) occurs between the two structural transitions at Pc ~ 8.0 GPa, concomitant with the emergence of superconductivity with Tc ~ 4.8 K. The superconductivity in NiPSe3 emerging in the 2D monoclinic phase coexists with the in-plane AFM order and continues into the 3D trigonal phase. Our electronic structure calculations reveal that the IMT and superconductivity in NiPSe3 are both related to the enhanced Se2− 4p and Ni2+3d electronic hybridizations under pressure. From these results, we construct a temperature-pressure electronic phase diagram of NiPSe3, revealing interesting relationships between magnetism and superconductivity.

Crystal Phase Refinement and Optical Features of Highly Efficient Green Light Radiating Ca9Y(VO4)7: Er3+ Nanophosphors for Emerging Solid-state Lighting Applications.

Ca9Y(VO4)7 phosphor activated with Er3+ ions have been developed by the urea-aided solution combustion technique. XRD profiles assisted with Rietveld refinement executed over-developed Er3+-activated Ca9Y(VO4)7 powder, revealed a trigonal phase with the R3c space group. The electron microscope techniques namely TEM and SEM characterize the size and surface-linked qualities of the developed nanopowder, respectively. The uniform distribution of various elements in the nanocrystalline sample is authenticated by an energy-dispersive spectroscopy (EDS) system. The Eg (band gap) value of 3.64eV for Ca9Y0.9Er0.1(VO4)7 and 3.74eV for Ca9Y(VO4)7 has been estimated. Upon 382nm excitation, Er3+: Ca9Y(VO4)7 phosphor gives rise to the bright green emission owing to the 4S3/2 → 4I15/2 transition. The concentration quenching after 10mol% composition of trivalent erbium ions is attributed to dipole-dipole interlinkages in accordance with Dexter's theory. The radiative lifetime (1.1083 ms), non-radiative rates (0.2079 ms- 1), quantum efficiency (79%), along with colorimetric parameters i.e. CIE x (= 0.2577), y (= 0.4566), and CCT quantities offer Ca9Y0.9Er0.1(VO4)7 as a proficient green radiating nanomaterial for RGB phosphors in solid-state applications.

Phase-Selective Epitaxy of Trigonal and Orthorhombic Bismuth Thin Films on Si (111).

Over the past three decades, the growth of Bi thin films has been extensively explored due to their potential applications in various fields such as thermoelectrics, ferroelectrics, and recently for topological and neuromorphic applications, too. Despite significant research efforts in these areas, achieving reliable and controllable growth of high-quality Bi thin-film allotropes has remained a challenge. Previous studies have reported the growth of trigonal and orthorhombic phases on various substrates yielding low-quality epilayers characterized by surface morphology. In this study, we present a systematic growth investigation, enabling the high-quality growth of Bi epilayers on Bi-terminated Si (111) 1 × 1 surfaces using molecular beam epitaxy. Our work yields a phase map that demonstrates the realization of trigonal, orthorhombic, and pseudocubic thin-film allotropes of Bi. In-depth characterization through X-ray diffraction (XRD) techniques and scanning transmission electron microscopy (STEM) analysis provides a comprehensive understanding of phase segregation, phase stability, phase transformation, and phase-dependent thickness limitations in various Bi thin-film allotropes. Our study provides recipes for the realization of high-quality Bi thin films with desired phases, offering opportunities for the scalable refinement of Bi into quantum and neuromorphic devices and for revisiting technological proposals for this versatile material platform from the past 30 years.

Synthesis–dependent structural and optoelectronic properties of semicrystalline LiNbO3:SiO2 hybrid silicates

Polycrystalline ceramics of lithium niobate (LNO) were prepared via standard hydrothermal and solid–state chemistry reactions, and by the sol–gel method implementing acrylamide polymerization. Congruent LiNbO3 trigonal perovskite phases crystallized in the R3c (161) space group [3 m (C3v) polar point group] were obtained in all cases. Depending on the implemented synthetic route, the average grain and crystallite sizes were estimated to 127–895 nm and 35–40 nm, respectively. As prepared LNO powders were embedded in a–SiO2 mesoporous sonogel networks at different doping rates to conform LiNbO3:SiO2 semicrystalline hybrid silicates with differentiated structural and optoelectronic (OE) properties. Intensive morphological, structural, spectroscopic, and nonlinear optical (NLO) characterizations were performed to explore these novel composites’ structural and photophysical properties for lead–free ferroelectric and optical applications. Results show that the massive porosity of the sonogel glasses and related defective bonding environment promote generalized host–guest molecular interactions influencing the oxidation states and radiative transitions of the dopant compounds via surface–assisted mechanisms and chemical charge–transfers. Additionally, due to the ferroelectric nature of LNO and average macroscopic alignment attained along the polycondensation stage of the solid solutions, SHG activity was observed from the hybrid sonogel (HSG) phases. Bulk NLO susceptibilities and molecular hyperpolarizabilities were estimated within the 9.62 × 10−11 and 10−23 esu range, respectively. Finally, depending on the synthesis methodology and in–gap hybridized levels, energy gap (Eg) narrowing was also observed for all LNO/HSG glasses, showing Eg values as low as 3.05 eV.

A new ternary derivative of the Laves phases in the Mg-Co-Ga system.

Crystal structures of MgCoGa, Mg0.74CoGa0.52 and Mg0.49CoGa0.15 phases from the Mg-Co-Ga system were investigated using single-crystal diffraction. These structures belong to the family of so-called Laves phases. Hexagonal MgCoGa crystallizes as a disordered phase within the MgZn2 structure type. The orthorhombic structure of Mg0.74CoGa0.52 is a distortion variant of MgZn2 and URe2 structure type, and the structural relation is demonstrated in terms of a Bärnighausen formalism group-subgroup transformation scheme. The structure of trigonal phase Mg0.49CoGa0.15 is strongly disordered, as is shown by the presence of adjacent atomic sites which cannot be occupied simultaneously. In Mg0.49CoGa0.15, two subcells (A and B) were obtained in a ratio of 9:1. Subcell A is closely related to MgZn2-type.

Thermal annealing induced linear/nonlinear properties of Ag2S/As2Se3 heterojunction films for optoelectronic applications

The present study reports the annealing induced structural as well as optical properties of Ag2S/As2Se3 heterostructure film at different annealing temperatures. The trigonal AgAsSe2 phase formation was confirmed from the X-ray diffraction (XRD) and selective area electron diffraction (SAED) study. The bandgap of as-prepared Ag2S/As2Se3 film decreased on annealing. The reduction in bandgap increased the static refractive index with annealing. The Urbach energy increased from 422±3 meV to 464±2 meV whereas the optical density and extinction coefficient increased by annealing due to the formation of AgS–AsSe solid solution. The dispersion energy increased and consequently increased the oscillator wavelength and oscillator strength upon annealing. The carrier concentration and optical conductivity increased whereas the optical electronegativity decreased with annealing. The 3rd order nonlinear susceptibility (χ(3)) increased from 2.804x10−11 esu (as-prepared Ag2S/As2Se3) to 5.132 x10−11 esu upon annealing at 200 °C. The n2 value increased upon annealing which increased the nonlinear absorption coefficient but decreased the figure-of-merit. The contact angle value decreased (93°–47.6°) that shows the transformation of hydrophobicity to hydrophilic nature which is good for sensor applications like biological sensor. The surface roughness decreased upon annealing. The change in optical parameters upon annealing makes them the appropriate candidate for optoelectronics, dielectric and nonlinear optical applications such as memory devices, optical switch, etc.