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The search for hard refractory materials has recently been attractive in the field of material science. The structural stability, electronic structure, and mechanical properties of noble metal carbides M2C and MC2 (M = Os, Ir, Pt) are investigated in tetragonal (P4/mbm), fluorite/antifluorite (Fm3m), orthorhombic (Pnnm), pyrite (Pa-3) and hexagonal (P6/mmm) phases for their potential ability and use as hard materials, by the first principles calculation based on density functional theory. It is found that M2C are most stable in anti-fluorite structure, while MC2 are stable in hexagonal structure. In Os2C and Pt2C, structural phase transition is predicted from antifluorite to pyrite whereas antifluorite to hexagonal in Ir2C and hexagonal to tetragonal in OsC2 and PtC2 under high pressure. Born-Huang criteria for mechanical stability are satisfied by the elastic constants of M2C and MC2. The bulk modulus of these materials is found to be high, which indicates that these materials are super hard materials.

A phenomenological Landau-Devonshire theory is applied to construct the thermodynamic potential of (110) oriented Ba(Zr0.08Ti0.92)O3 thin film and investigate the phase transition, ferroelectric, dielectric and piezoelectric properties. Three ferroelectric phases, such as tetragonal a1 phase, orthorhombic a2c and triclinic γ phase are stable in “misfit strain-temperature” phase diagram. Two triple points are found in the phase diagram and 90° polarization switching can occur directly between tetragonal a1 phase and orthorhombic a2c phase. Complicated phase transitions are induced by the electric field in triclinic γ phase due to the nonlinear coupling terms appeared in the thermodynamic potential. The longitudinal piezoelectric coefficient of (110) oriented Ba(Zr0.08Ti0.92)O3 thin film is smaller than that of (001) oriented film. Moreover, negative longitudinal piezoelectric coefficient can be obtained in triclinic γ phase.

Thermoelectric materials are useful for conversion of waste heat to electrical energy. Doping effects on electronic structure and transport properties of the orthorhombic and tetragonal phases of BaCu 2 S 2 has been studied using a combination of density functional theory and semi-classical Boltzmann transport theory. Al, Ga, In and Tl from Group 13 and Sb and As from Group 15 were used as a dopant. Amongst the dopants considered in this study the Group 13 elements introduce resonant states at the bottom of the conduction band of the orthorhombic phase. From the transport property calculations we predict Ga to be the most effective dopant that results in the largest enhancement of the Seebeck coefficient and power factor. However, taking into account the electronic contribution to thermal conductivity, we observe that Tl doping results in best value of electronic Z T .

Selected structural and elastic properties of an orthorhombic SnSe at an ambient pressure and under high pressures were investigated using first-principles calculations. At ambient pressure, the calculated structural parameters and elastic constants show a good agreement with previously reported values. Effects of pressure on structural and elastic properties were presented and discussed in detail. Moreover, the pressure dependence of selected structural and elastic properties, which relate to phase transition from an orthorhombic phase to the high-pressure phase, was analyzed. We suggested that the phase transition is related to the compression along the c- and b-axis which correspond to C33 and C22, respectively.

Pressure is a useful tool to profoundly modify the volume and electronic structure of materials, resulting in the formation of new structures with exotic physical and chemical properties. The high-symmetry cubic barium fluoride (BaF2) with a space group of Fm-3m (Z = 4) is the prototypical fluorite-type compounds at ambient condition, which is shared with many alkaline-earth fluorides. The study of high-pressure evolution of the BaF2 phase is of fundamental importance in helping to understand the structural sequence and principles of crystallography. In this work, we here have systematically investigated the high-pressure structural transition of BaF2 up to 200 GPa using an effective CALYPSO methodology. Strikingly, two thermodynamically favored phases with orthorhombic Pnma and hexagonal P63/mmc symmetry are found at 3.6 and 19.2 GPa, respectively. Distinguishingly, P63/mmc phase remains stable up to 90.5 GPa, and then transform to Pnma structure. Further electronic calculations indicate that BaF2 maintains insulating feature until 200 GPa. Our current results have broad implications for other AB2-type compounds that may harbor similar novel structured evolution behavior at high pressure.

Glycine Nitrate Process (GNP) was used to obtain orthoferrites YFeO3 (YFO) nanoparticles. The structural phase formation of compound was confirmed by using XRD and Raman spectroscopy. Morphological, thermal, ferroelectric and magnetic properties at room temperature have been systematically studied via TEM, TG-DSC, Mossbauer, PE loop, and SQUID. Single phase YFeO3 nano-crystals with orthorhombic Pnma space group were successfully derived from GNP with average crystallite size 50–60 nm. The magnetic hysteresis loops indicates Fe spins orders antiferromagnetically with weak ferromagnetism due to the superexchange and Dzyaloshinski-Moriya (DM) antisymmetric exchange mechanism. The vibrational properties were characterized by Raman spectroscopy, in which 12 active modes were observed out of 24 Raman active modes. Spin-exchange striction is considered as a microscopic origin of ferroelectric polarization. The evidence for the ferroelectric character of the samples is observed in the saturation polarization loops at room temperature. Mossbauer spectra and XPS show that the Fe3+ is dominated in the compound.

The structural and magnetic properties of Pr1-xLaxMnO3 (0 ≤ x ≤ 1) polycrystalline powders are investigated. A structural phase transition from a large Jahn-Teller (J-T) distorted orthorhombic structure to a small J-T distorted orthorhombic phase is found at x = 0.70, while the LaMnO3 is showed to have a rhombohedral structure. All the samples exhibit ferromagnetic ordering, and meanwhile, a reentrant spin glass behavior at low temperature. The relationship between J-T distortions and the ferromagnetic order is discussed.

Orientation dependence of phase diagrams and physical properties of Ba0.6Sr0.4TiO3 films are investigated by using a phenomenological Landau-Devonshire theory. New ferroelectric phases, such as the tetragonal a 1 phase and the orthorhombic a 2 c phase in (110) oriented film and the monoclinic M A phase in (111) oriented film, appear in the “misfit strain-temperature” phase diagrams as compared with (001) oriented film. Moreover, the phase diagrams of (110) and (111) oriented films are more complex than that of (001) oriented film due to the nonlinear coupling terms appeared in the thermodynamic potential. The dielectric and piezoelectric properties largely depend on the misfit strain and orientation. (111) oriented film has the better piezoelectric property than (110) oriented film. Furthermore, the compressive misfit strain is prone to induce the larger piezoelectric property than tensile misfit strain.

The structural, electrical, magnetic, and thermal properties of electron beam (EB) irradiated PrMnO3 manganites were investigated in the present communication. X-ray diffraction data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). Furthermore, the diffracted data are analyzed in detail using Rietveld refinement technique. It is observed that the EB dosage feebly disturbs the MnO6 octahedra. The electrical resistivity of all the samples exhibits semiconducting behavior. Small polaron hopping model is conveniently employed to investigate the semiconducting nature of the pristine as well as EB irradiated samples. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit large positive values at lower temperatures, signifying holes as the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism assists the thermoelectric transport property in the high temperature region. The magnetic measurements confirm the existence of paramagnetic (PM) to ferromagnetic (FM) behavior for the pristine and irradiated samples. In the lower temperature regime, coexistence of FM clusters and AFM matrix is dominating. Thus, the complex magnetic behavior of the compound has been explained in terms of rearrangement of antiferromagnetically coupled ionic moments.

The structure of La doped BiFeO3, prepared by the conventional hydrothermal method, were investigated at room temperature using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy. The XAFS spectra showed that La in fact substitute the Bi site of secondary nanosized particles with orthorhombic symmetry instead of the long-believed rhombohedral R3c phase at low-content doping. The pressure-induced phase-transition sequences of La-doped BiFeO3, which mixed nanoscale orthorhombic symmetry in the R3c crystal structure were investigated using synchrotron radiation X-ray diffraction up to 27.3 GPa. Our experimental data clearly showed that rohombohedral (R3c) phase first transforms to monoclinic (C2/m) phase at 6.5 GPa, then to orthorhombic (Pnma) phase at 13.5 GPa, and the coexistence of multiple intermediate phases are observed before two transitions, revealing that the doping-induced nanoparticles with orthorhombic structure did drive the change in symmetry and transition pressure.

This paper aims to study spectroscopy, thermal, dielectric, and photoluminescence properties of [C6H5NH3]3BiCl6·3H2O, which was investigated elswehere [Orthorhombic system P212121 (Z = 4)]. Indeed, the simulated crystal morphology made with the Bravais, Friedel, Donnay and Harker (BFDH) method is very close to the experimental observation taken under scanning electronic microscopy (SEM). The Raman spectrum (50-3400 cm−1) at ambient temperature is interpreted considering the D2 factor group, in which the BiCl63− anions occupied C1 (2) symmetry sites. The Infrared spectra, recorded at ambient temperature and 140 °C, are studied to confirmed the removing of water molecules above the compound dehydratation. The dehydratation-decomposition behaviour of [C6H5NH3]3BiCl6·3H2O is studied by the differential scanning calorimetry (DSC) analyses (5 °C.min−1), which shows that the title compound is decomposed immediately above the dehydration process at 130 °C. The thermal behaviour study is supported by the dielectric analyses, performed in the (20–150 °C) temperature domain and (50 kHz - 1 MHz) frequencies. So, three dielectric permittivity (er) anomalies (T1 = 85 °C, T2 = 115 °C, T3 = 126 °C) are shown in agreement with the DSC analyses; the (er) dispersion across the dehydratation process implied the appearance of electric conductivity. The variation of the dielectric dissipation tgδ versus temperature at (50 kHz - 1 MHz) is studied. The fluorescence excitation and emission spectra show that the compound undergoes indigo-blue photoluminescence (PL) with two emission signals at 414 nm (2.991 eV) and 424 nm (2.921 eV), when it was excited at 400 nm (3.096 eV) (λmax excitation). This suggests potential applications for this compound as UV detection and optical materials.

The single-phase Nd1-xSrxNiO3 (x = 0–0.3) polycrystalline samples were successfully synthesized, and the structure, resistivity, and magnetic property were investigated. All of samples were well indexed to an orthorhombic structure with Pnma space group. With increasing Sr concentration x, the lattice parameter a decreased, the lattice parameter b and c increased, the obtained unit-cell volume systematically increased due to the larger ion radius of Sr2+ than Nd3+. Sr partial substitution for Nd suppressed the metal-insulator and antiferromagnetic transition until x = 0.2. However, as the Sr content increased to 0.3, some abnormal phenomena were observed. The present work shows that physical properties are correlated with the evolution of perovskite tolerance factor in Nd1-xSrxNiO3 system.

Pressure effect on lattice parameters, elastic moduli, Poisson's ratio, Cauchy pressure, elastic anisotropy, and Vickers hardness of orthorhombic MgSiN2 by means of first-principles calculations based on density functional theory (DFT) by generalized gradient approximation (GGA) in the functional form by Perdew, Bruke, and Ernzerhof (PBE) of the exchange-correlation were presented. The structural properties, elastic moduli, B0/G, Poisson's ratio (ν) and Cauchy pressure under pressure up to 10 GPa were calculated. The optimized structural and ground state properties under ambient pressure were in agreement with the available experiments and other calculations. The orthorhombic MgSiN2 was mechanically stable under pressure up to 10 GPa by the elastic stability criteria investigation. Under pressure, the relationship of elasticity in length was C33 > C11 > C22, indicating that it is easier to compress along the b-axis than along the a-axis and c-axis, respectively. The calculated bulk modulus, shear modulus, Young's modulus and Poison's ratio index all increased with an increase in the pressure. The B0/G, Poisson's ratio (ν) and Cauchy pressure analyses implied that orthorhombic MgSiN2 was single crystal, and a critical pressure for brittle-to-ductile transition was found to be 2 GPa. The Cauchy pressure of {100} plane, {010} plane and {001} plane, Vickers hardness (Hv) and the shear anisotropy as a function of pressure were investigated from the calculation.

Lead free KNN (K0·5Na0·5NbO3) ceramics was obtained via the conventional solid state sintering technique. The ceramics synthesized was characterized for their phase transition analysis, crystal structure, morphology and electrical properties. The powder X-ray diffraction (XRD) patterns confirmed single phase of KNN with orthorhombic crystal system at room temperature. Scanning electron microscopy (SEM) of the sintered KNN revealed the existence of densification and comparable size of the grains. Two phase transitions were observed in ϵr-T graph: orthorhombic to tetragonal at TO-T (~236 °C) and tetragonal to cubic at TT-C (~440 °C) for 1 kHz frequency. The decrease in the net polarization of the material with the increase in frequency leads to the decrease in the value of ϵr and tanδ. Three characteristic Raman peaks observed at (~262 cm−1, ~617 cm−1 and ~858 cm−1) correlate the structure and ferroelectric properties of KNN materials. These promising outcomes demonstrate that KNN-based lead-free ceramic composition is potential candidate to substitute lead-based materials for various applications.

Perovskite-type materials have been attracted due to their relevant applications in memory devices, tunable microwave displays, oxygen-permeable membranes, sensors, and capacitors. An attempt has been made here to analyze the structure of (Ba0.5Sr0.5)(Fe1-xCex)O3-ẟ (x = 0–1.0) oxides by Rietveld refinement under different space groups. It possesses cubic (space group Pm3m, Z = 1), cubic with orthorhombic, and orthorhombic (space group Pnma, Z = 4) structures for the composition x = 0, 0.10–0.60, and 0.80–1.0, respectively. The amount of cubic phase decreases from 100% to 24% with cerium content (x) = 0–0.60 and complete transformation to the orthorhombic phase occurred at x = 0.80. Moreover, single – dual - single structural phase transitions have been observed. The average bond length decreases with cerium content. The bond angles along O–B–O and B–O–B are deviated significantly due to the tilting and rotation of (Ce,Fe)O6 octahedra. The presence of distortion/oxygen vacancies makes the compound useful in industrial applications.

Magnetic properties and magnetocaloric effect of Ho2PtSi3, a new ternary intermetallic compound with the orthorhombic Ba2LiSi3-type structure, are studied by dc magnetization, ac susceptibility, magnetic relaxation, specific heat, and magnetic memory effect measurements. The experimental results indicate that this system undergoes a magnetic phase transition from a paramagnetic state to a ferromagnetic cluster state at a temperature TC ~ 6.5 K followed by a cluster glass transition at Tf ~ 5.8 K. The typical cluster glass features observed below Tf for Ho2PtSi3 include (1) broad peak in specific heat curve, (2) frequency dependent cusp in ac susceptibility curve, (3) evident irreversible magnetism, (4) long-time magnetic relaxation behavior, and (5) zero-field-cooling magnetic memory effect. On the other hand, the large values of magnetic entropy change, relative cooling power and adiabatic temperature change are estimated near TC under a field change. These results suggest that Ho2PtSi3 can be classified as a huge ferromagnetic cluster glass system with large magnetocaloric effect.

To understand the structural changes with respect to the CH 3 NH 3 groups during the phase transitions in (CH 3 NH 3 ) 2 MnCl 4 , 1 H magic-angle spinning nuclear magnetic resonance (MAS NMR) experiments were performed. The two types of protons in CH 3 NH 3 were distinguished by 1 H MAS NMR. The 1 H chemical shift of NH 3 exhibited a larger variation with temperature than that of CH 3 . The Mn 2+ in (CH 3 NH 3 ) 2 MnCl 4 was bonded to the Cl atom H-bonded to NH 3 and was paramagnetic, directly affecting the environment of 1 H in NH 3 . The larger C‒H and shorter N‒H bond lengths in CH 3 NH 3 gave rise to a larger (T 1ρ ( l )) and shorter (T 1ρ ( s )) spin-lattice relaxation times of the corresponding proton. The phase transitions were not governed by structural changes in CH 3 NH 3 , whereas the ferroelastic domain-wall structures for phases II and III were found to be the main reason for the occurrence of phase transitions.

The effect of Cu substitution on the martensitic transition and magnetocaloric properties of arc-melted Ni 50−x Cu x Mn 39 Sn 11 (x = 6 and 7) Heusler alloys are investigated by differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy and magnetic measurements. According to XRD patterns, while Ni 44 Cu 6 Mn 39 Sn 11 alloy exhibit orthorhombic structure, Ni 43 Cu 7 Mn 39 Sn 11 alloy crystallize cubic L2 1 structure at room temperature. The substitution of Cu for Ni leads to decreasing on the martensitic transition temperatures to lower values. The magnetic entropy changes calculated from M(T) curves, for avoiding hysteresis losses in the vicinity of the martensitic transition region, by using Maxwell relation. The maximum magnetic entropy change, Δ S M is found 11.0 J kg −1 K −1 for Ni 43 Cu 7 Mn 39 Sn 11 alloy around the martensitic transition region, which is nearly twice as large as the Ni 44 Cu 6 Mn 39 Sn 11 alloy under the magnetic field changing from 0 to 2 T.

A phenomenological Landau-Devonshire theory is applied to investigate the phase diagrams and physical properties of (110) oriented Ba x Sr 1 − x TiO 3 films. New ferroelectric phases, such as the tetragonal a 1 phase and the orthorhombic a 2 c phase, appear in the “misfit strain-temperature” phase diagrams for (110) oriented films compared with that of (001) oriented films. Moreover, the orthorhombic a 2 c phase, and the tetragonal c phase and the triclinic γ phase are stable at low temperature for x = 0.5 and x = 0.7 , respectively. The ferroelectric, dielectric, and piezoelectric properties strongly depend on the misfit strain and electric field. (110) oriented Ba 0.7 Sr 0.3 TiO 3 film has the larger ferroelectric polarization and piezoelectric coefficient than that of Ba 0.5 Sr 0.5 TiO 3 film. The giant piezoelectric coefficient of 340 pm / V is obtained at the electric field of 50 KV / cm in (110) oriented Ba 0.7 Sr 0.3 TiO 3 film, which is comparable with the values of Pb ( Zr 1 − x Ti x ) O 3 and ( 1 − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 − xPbTiO 3 films. It makes (110) oriented Ba x Sr 1 − x TiO 3 films suitable for applications in electromechanical devices.

Using the first-principles calculations, we have computed the structural parameters, band structures, elastic, dielectric and optical properties of TiSiO 4 in orthorhombic CrVO 4 -type ( Cmcm ), tetragonal zircon-type ( I 4 1 / amd ) and scheelite-type ( I 4 1 / a ) phases. The obtained structural parameters of three phases were in agreement with previous results. The band structures, density of states and bond populations have been given to analyze the electronic properties and chemical bondings. The independent elastic constants of three phases have been calculated, showing that all of them were mechanically stable. The CrVO 4 phase showed a brittle manner and the others behaved in a ductile manner. Moreover, the permittivity, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function and optical conductivity of three phases have been obtained and analyzed.

It has been well established that LaCrO3 exhibits an orthorhombic structure (Pnma) and undergoes a structural phase transition to rhombohedral (R-3c) when submitted to physical or chemical pressure. The doping-induced structural phase transition in the LaCr1-xAlxO3 solid solution is carefully investigated by Raman Spectroscopy in this communication. Spectral band analysis of the experimental results strongly indicates that solid solution with low Al-content (x = 0.0 and 0.05) displays an orthorhombic structure characterized by the Ag, B1g, B2g, and B3g vibrational modes, whereas the solid solution with high Al-content (x = 0.5 and 0.95) displays a rhombohedral structure with A1g and Eg vibrational modes. Particularly, the decrease of intensity and the displacement of some vibrational modes with increasing of Al-content indicates that the structural phase transition from orthorhombic to rhombohedral in the LaCr1-xAlxO3 solid solution is accompanied by a freezing of the (Cr/Al)O6 octahedron vibrations. It is therefore postulated that the Al-doping in LaCrO3 above a threshold leads to instability and structural distortions that induce a structural phase transition.

The manuscript presents a systematic study of ferroelectric, piezoelectric and conduction behaviour of Sm, Na substituted Strontium Bismuth Titanate ceramics, prepared by solid-state reaction method. The structural analysis of Bismuth layer structured ferroelectrics (BLSF) of Sr1-2xSmxNaxBi4Ti4O15 (SSNBTi) ceramics was done by X-ray Diffraction technique and it showed single-phase formation and peak shifting towards the higher angles. Scanning Electron Microscopy confirmed orthorhombic sheet-like grain structure with random orientation of grains. P-E study and Piezoelectric studies were done at room temperature (RT); improved remnant polarization (Pr = 1.95 μC/cm2), Piezoelectric charge coefficient (d33 = 21.1 pC/N) and electromechanical coupling factor (kp = 0.71) were achieved by substitution of Sm, Na (x = 0.4) in Sr of SBTi ceramics. The AC conductivity was studied from RT to 600 °C in the frequency range of 1 kHz–100 kHz. The trends shown by Activation energies obtained from Arrhenius plots suggests that the mechanism of conduction is through short-range oxygen vacancies hopping. The combination of improved ferroelectric properties and high piezoelectric constant (kp = 0.71) make the SSNBTi ceramics suitable for a wide range of sensor, actuator, and transducer applications.

In this work, we investigated the apparent coexistence of superconductivity and magnetism in polycrystalline Bi 3 Ni 1− x Fe x samples for low concentrations of iron ( 0 ≤ x ≤ 0.10 ). The compound was synthesized by the solid-state reaction method and characterized by X-ray diffraction and magnetic measurements. From X-ray, it was observed that the main phase corresponds to an orthorhombic structure with space group Pnma and shows no dependence on the Fe concentration. From magnetic measurements, it was observed that the critical temperature was not affected by iron doping and that ferromagnetism and superconductivity coexist apparently in an interesting interplay.

The phase diagram and pyroelectric effect of (110) oriented Pb ( Zr 1 − x Ti x ) O 3 thin films with different Ti composition are investigated by a phenomenological Landau–Dovenshire theory. The tetragonal ( a 1 ) phase, the orthorhombic ( a 2 c ) phase, and the triclinic (γ) phase are stable. The compressive misfit strain favors the orthorhombic ( a 2 c ) phase, whereas the tensile misfit strain makes the triclinic (γ) phase and the tetragonal ( a 1 ) phase stable. At room temperature, the misfit strain induces the first order phase transition from the orthorhombic a 2 c phase to the triclinic γ phase in the Pb ( Zr 1 − x Ti x ) O 3 (x=0.4, 0.5, 0.6) thin films. Moreover, even in the γ phase of Pb ( Zr 1 − x Ti x ) O 3 (x=0.4, 0.5) thin films, the first order γ1–γ2 phase transition may happen with increasing the tensile misfit strain. The Pb ( Zr 0.5 Ti 0.5 ) O 3 thin film with the Ti composition around the morphotropic phase boundary has the largest dielectric and pyroelectric properties, which is in agreement with the experimental result. A critical electric field exists and results in the non-monotonic variation of dielectric and pyroelectric properties with the misfit strain in Pb ( Zr 0.5 Ti 0.5 ) O 3 thin film. The positive pyroelectric coefficient is obtained in the γ2 phase of Pb ( Zr 1 − x Ti x ) O 3 (x=0.4, 0.5, 0.6) thin films.

The full-potential linearized augmented plane wave (FPLAPW) method based on the density functional theory within the GGA and GGA+U, is used to investigate the structural, magnetic and half-metallic properties of the Pnma orthorhombic Cerium orthoferrite (CeFeO 3 ) and Cerium orthochromite (CeCrO3). The calculated densities of states presented in this study identify the metallic behavior CeFeO3 when we use the GGA scheme, whereas when we use the GGA+U, we see that its exhibits half-metallic character with an integer magnetic moment of 24 μB per formula unit at its equilibrium volume. CeCrO3 is half-metallic for both approaches and of n type conductivity for GGA but p type conductivity for GGA+U. It is found that the majority of the magnetic moments of both compounds originate from the cerium sites since the f states of Ce are spin polarized. From the band structure and the densities of states analysis, we find that CeCrO3 and CeFeO3 are strong candidates for spintronic applications.

The effects of Al content on microstructure, phase transformation and activation energy of Ti–12V-xAl (x = 2, 4 and 6 wt %) alloys produced by using the arc-melting technique have been investigated in the present study. These features of the alloys were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The XRD and SEM measurements showed that the alloys had simple of single orthorhombic α martensitic phase. In the DSC analysis, it was observed that the martensitic transformation temperature decreased depending on the heating rate in the alloys. The highest transformation temperature occured in the Ti–12V–4Al alloy. In TEM images, it was noteworthy that there were martensite structures arranged side by side in the structure of the alloys. The activation energies of the alloys were estimated using the Kissenger and Osawa method using the data obtained from DSC. Activation energies determined by these two methods were similar.

The magnetocaloric effect in orthorhombic MnCoGe1−xCux (x = 0.0–0.35) alloys are investigated by combining density functional theory (DFT) and Monte-Carlo simulation. The long-range interactions of the magnetic exchange coupling constants evaluated by the DFT calculations are considered for the Monte-Carlo simulation. The magnetic phase transition temperature is estimated by the divergence of the specific heat, and the isothermal entropy change is computed by integrating the isothermal magnetization curves with the Maxwell relation. The magnetic exchange coupling constants of the Mn-Mn pairs is decreased significantly with increasing of the concentration of Cu from 0.0 to 0.35, resulting in the rapid decrease of the Curie temperature from 618 K to 28 K. Not only the Curie temperature of the MnCoGe alloy is controllable by changing the concentration of Cu at Ge site, but also the magnetocaloric properties such as isothermal magnetic entropy change and relative cooling power are strongly dependent on the concentration of Cu.

We investigated the crystal structure, electronic structure, elastic stiffness constants, responses to tensile and shear deformations, lattice vibrational modes as well as vibration heat capacity and vibration entropy of the orthorhombic YSi compound using ab initio approach. The relaxed ground-state lattice constants a, b and c of YSi exhibit fair agreement with the available experimental and theoretical data. Nine independent elastic stiffness constants have been computed by increasingly varying minute strains based on “energy-strain” approach, which confirm that the orthorhombic YSi is mechanically stable. Some polycrystalline moduli involving bulk modulus, Young's modulus and shear modulus, Poisson's ratio, brittle/ductile characteristic have also been systematically derived, and YSi can be classified as brittle compound. Both three-directional Young's modulus anisotropy and bulk modulus anisotropy are calculated in detail, and the calculations indicate that the orthorhombic YSi takes on significant elastic anisotropy. We further studied the theoretical tensile and shear strengths under different loads. Also, the phonon spectra, total and partial phonon densities of states are researched by employing Density Functional Perturbation Theory (DFPT) and the finite-displacement method, and the infrared-active and Raman active vibration modes at the center of Brillouin zone are classified using the group theory. Moreover, we predicted the constant volume heat capacity of YSi under high temperature relying on the calculated phonon densities of states as well as quasi-harmonic approximation (QHA) and Debye model.

A new superhard carbon allotrope oC48 is uncovered. The mechanical and electronic properties of oC48 were studied by using first principles calculations. The calculated results of elastic constants and phonon dispersion show that oC48 is mechanically and dynamically stable. The hardness of oC48 is predicted to be 73.3 GPa, which indicates the superhardness of oC48. The elastic anisotropy of oC48 were also analyzed in detail. The band structure of oC48 shows that it is an indirect band gap semiconductor with a band gap of 1.464 eV.

Coupling effects among spin, charge, and lattice in a strongly correlated system are critical for next generation spintronic and data storage devices. However, the complex effects are elusive and difficult to distinguish their contributions to polarization modulation. Here we tailored the polarization by co-doping of non-magnetic Y and Eu at A-sites in DyMn2O5. The structure, specific heat, magnetism, and ferroelectricity of the polycrystalline Dy1-x(Eu0.24Y0.76)xMn2O5 ceramics were comprehensively explored. Interestingly, the co-doping does not cause lattice distortion of DyMn2O5, and all the ceramics are orthorhombic structures, while the independent Dy3+ spin order and the Dy3+-Mn3+ coupling can be suppressed. With increasing the co-doping content x, the spins related properties associated with the Dy3+-Mn4+-Dy3+ sub-lattice are progressively inhibited, while they keep less disturbance in the Mn3+-Mn4+-Mn3+ block. Moreover, the spin coupling of Dy3+-Mn3+ ions is stronger again the magnetic field than that of Dy3+-Mn3+. Our results enhance the understanding of ferrielectricity in DyMn2O5, and provide a method for controlling the polarization in the multiferroic manganite coexisting 3d and 4f elements.

The Ba1-xCaxTi1-ySnyO3 (abbreviated as BCxTSy, x = 0.01, y = 0.01; x = 0.03, y = 0.015; x = 0.05, y = 0.02; and x = 0.07, y = 0.025 mol.) electroceramics were synthesized by solid-state reaction method and investigated their structural, dielectric, ferroelectric and piezoelectric properties. Rietveld refinement of X-ray diffraction data for the composition x = 0.03, y = 0.015 reveals the phase co-existence of two non-centrosymmetric orthorhombic (Amm2) (7.71%) + tetragonal (P4mm) (92.29%) lattice symmetries near room temperature which is also evidenced by temperature-dependent Raman and dielectric studies. All compositions reveal the dense microstructure having relative density ~92%–96% and average grain size ~10.7–22.5 μm. The phase diagram based on dielectric study suggests that the composition x = 0.03, y = 0.015 reveals T(R–O) ~ − 60 °C, T(O-T) ~ 19 °C and TC ~ 126 °C with Pr = 11.80 μC/cm2, Ec = 3.5 kV/cm, Pmax = 21.92 μC/cm2, d33* = 505.5 pm/V, d33 = 287 pC/N and electrostrictive coefficient (Q33) = 0.036 m4/C2 properties which could be useful for developing the piezoelectric AC devices. Here, we have achieved the phase-coexistence of two non-centrosymmetric lattice symmetries near room temperature to invoke the reliable ferroelectric and piezoelectric properties and discussed the results with the structure-property-composition relation.

A first-principles based atomistic scheme is used to investigate the dielectric and piezoelectric properties of BiFeO3. The atomistic model fitted from first-principles calculations reproduces very well the structural and polar properties of the material at finite temperature, predicting a direct transition from a lowerature R3c ferroelectric phase to a Pbnm orthorhombic phase in agreement with experiments. We use this theoretical approach to calculate intrinsic single crystal properties, which are difficult to obtain from experiments due to decomposition and leakage problems. The whole set of dielectric and piezoelectric coefficients for BiFeO3 is computed as a function of temperature, together with the orientation dependence of the longitudinal coefficient d33∗. Fil: Graf, Mónica Elisabet. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Sepliarsky, Marcelo Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Machado, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Stachiotti, Marcelo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina

Using the full potential linear augmented plane wave (FPLAPW) method based on density functional theory (DFT), we have studied the structural, electronic, optical and magnetic properties of the orthorhombic perovskite oxide NdMnO 3, with both generalized gradient approximation (GGA) and GGA+ U approaches, where U is on-site Coulomb interaction correction. We have analyzed the structural parameters, total and partial densities of states. The results show a half-metallic ferromagnetic ground state for NdMnO3 in GGA+ U due to the strong hybridization effect between Mn 3d and Nd 4 f states The integer value of the total magnetic moment is one of the significance of the half metallic nature of this material. Furthermore, we have computed optical properties of NdMnO 3 ; we found pronounced peaks occurring in different parts of the spectrum. The results obtained, make the orthorhombic NdMnO 3 a promising candidate for application in spintronics and opto-electronics.

First-principles calculations are performed to simulate hydrostatic pressure and misfit strain effect on PbNiO 3 (PNO) material. Significant difference between hydrostatic pressure and misfit strain effect is discovered. That is (1) a hydrostatic-pressure-induced phase transition from a rhombohedral R 3 c phase to an orthorhombic Pnma phase emerges around 6 GPa; and (2) an epitaxial-strain-induced phase transition from a monoclinic Cc phase (the sequel to a monoclinic distortion from R 3 c ) to an orthorhombic Pbnm phase occurs about −3.3% misfit strain. Besides, the behaviors of oxygen octahedra tilting, polarization and the magnetic ordering temperature T N have been found to be strikingly affected by the variation of hydrostatic pressure and misfit strain, respectively. Finally, origins of the induced phase transitions are revealed.

Vanadium doped barium germanate microrods have been prepared by a facile hydrothermal process. The obtained vanadium doped barium germanate microrods are proved to be hexagonal BaGe 4 O 9 and orthorhombic Ba 2 V 2 O 7 phases by X-ray diffraction. Scanning electron microscopy shows that the vanadium doped barium germanate products consist of microrods with the diameter of microscale size. The diameter of the mirorods decreases from 800 nm to 150 nm with the vanadium doping mass percentage increasing from 1% to 10%. Solid UV–vis diffuse reflectance spectra show that the band gap of the vanadium doped barium germanate is smaller than that of the undoped barium germanate. The photocatalytic activity has been greatly enhanced by the vanadium doping. The vanadium doped barium germanate microrods exhibit great application potential for the photocatalytic degradation of methylene blue under solar light irradiation.

In this paper, the surface properties of the (001) surface in PrMnO3 are investigated using the projector augmented plane wave (PAW) methods within the spin-polarization generalized gradient approximation (GGA+U), where U is on-site Coulomb interaction correction. The result of the total density of states shows a half-metallic ground state for PrMnO3 in GGA+U treatment. The optimized structure parameters of both cubic and orthorhombic bulk phases are obtained. The electronic properties of the cubic PrMnO3 (001) surface with PrO- and MnO2-terminations are discussed. Based on the results of the calculated surface energies, we predict the surface energies of three low-index surfaces follows the sequence of (001)

Using first-principles theoretical techniques within density functional theory and many-body perturbation theory we investigated the structural and electronic properties of two LiInSe2 crystal modifications, orthorhombic (β-NaFeO2-type) and tetragonal (CuFeS2-type), focusing on the interband transitions and band gaps. It is found that the Tran-Blaha (TB09) functional predicts LiInSe2 to be a direct-gap semiconductor with a significantly larger band gap as compared with that from common local-density and gradient-corrected functionals. The most accurate values of the fundamental energy gaps are calculated within quasiparticle GW approximation and found to be 2.95 eV for the orthorhombic phase and 2.85 eV for the tetragonal one, with equal pressure coefficients of 63 meV/GPa. Our theoretical results eliminate the uncertainty in the band gap of LiInSe2. Moreover, the data obtained define the upper limit of the band gap of solid solutions (Cu,Li)InSe2 and (Ag,Li)InSe2, which can be of interest for applications in optoelectronics.

We have studied the critical behavior around the ferromagnetic–paramagnetic (FM–PM) phase transition (the Curie temperature, TC) of a polycrystalline manganite Pr0.7Ca0.15Ba0.15MnO3. The assessments based on Banejee׳s criteria reveals the sample undergoing a second-order magnetic phase transition. The use of the modified Arrott and Kouvel–Fisher methods determined the values of critical parameters TC≈117 K, β=0.403±0.024 and γ=1.242±0.033. With these values, magnetic-field dependences of magnetization at temperatures around TC (M–H–T curves) can be well described by the universal function of M ( H , e ) = | e | β f ± ( H / | e | β + γ ) , where e=(T−TC)/TC, and f+ and f− are regular functions for T>TC and T