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1.
The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO3 crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange‐correlation density functional theory (DFT) functionals for four stable phases of BaTiO3. A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO3. The comparative phonon symmetry analysis in BaTiO3 four phases has been made basing on the site symmetry and irreducible representation indexes for the first time. © 2012 Wiley Periodicals, Inc. 相似文献
2.
《Journal of computational chemistry》2017,38(24):2088-2099
Hybrid density functional theory calculations were performed for the first time on structure, stability, phonon frequencies, and thermodynamic functions of hafnia‐based single‐wall nanotubes. The nanotubes were rolled up from the thin free layers of cubic and tetragonal phases of HfO2. It was shown that the most stable HfO2 single‐wall nanotubes can be obtained from hexagonal (111) layer of the cubic phase. Phonon frequencies have been calculated for different HfO2 nanolayers and nanotubes to prove the local stability and to find the thermal contributions to their thermodynamic functions. The role of phonons in stability of nanotubes seems to be negligible for the internal energy and noticeable for the Helmholtz free energy. Zone folding approach has been applied to estimate the connection between phonon modes of the layer and nanotubes and to approximate the nanotube thermodynamic properties. It is found that the zone‐folding approximation is sufficiently accurate for heat capacity, but less accurate for entropy. The comparison has been done between the properties of TiO2, ZrO2, and HfO2. © 2017 Wiley Periodicals, Inc. 相似文献
3.
Saumya Tiwari P. C. Mishra S. Suhai 《International journal of quantum chemistry》2008,108(5):1004-1016
Geometries of the normal (N) and zwitterionic (Z) forms of glycine (gly) and their complexes gly.(H2O)n, n = 0–2, were fully optimized in gas phase and aqueous media, and transition states located between the corresponding N and Z forms. The geometry was also optimized and vibrational spectra calculated for the gly.(H2O)3 complex of Z glycine. Density functional theory at the B3LYP/AUG‐cc‐pVDZ level was employed for the geometry optimization calculations in gas phase and aqueous media while single point energy calculations were performed at the MP2/AUG‐cc‐pVDZ level in each case. Solvation in bulk water was treated using the polarizable continuum model (PCM). Zero‐point energy correction to total energy and thermal energy correction to enthalpy were obtained at the B3LYP/AUG‐cc‐pVDZ level of theory in both gas phase and bulk aqueous media and these corrections were also considered to be valid for the corresponding single point energy calculations performed at the MP2/AUG‐cc‐pVDZ level of theory. When geometries of the complexes of glycine with water molecules are optimized in aqueous media, the calculated properties are found to be appreciably modified with respect to those obtained by gas phase geometry optimization followed by solvation in aqueous media. For several vibrational frequencies, the agreement between the calculated and experimentally observed results is improved appreciably when both the specific and bulk solvent effects are considered in combination with full geometry optimization in aqueous media. For certain vibrational frequencies, mode assignments have also been modified. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
4.
Robert A. Evarestov Andrei V. Bandura Dmitrii D. Kuruch 《Journal of computational chemistry》2013,34(3):175-186
The first‐principles calculations using hybrid exchange‐correlation functional and localized atomic basis set are performed for BaTiO3 (BTO) nanolayers and nanotubes (NTs) with the structure optimization. Both the cubic and the ferroelectric BTO phases are used for the nanolayers and NTs modeling. It follows from the calculations that nanolayers of the different ferroelectric BTO phases have the practically identical surface energies and are more stable than nanolayers of the cubic phase. Thin nanosheets composed of three or more dense layers of (0 1 0) and (0 1 ) faces preserve the ferroelectric displacements inherent to the initial bulk phase. The structure and stability of BTO single‐wall NTs depends on the original bulk crystal phase and a wall thickness. The majority of the considered NTs with the low formation and strain energies has the mirror plane perpendicular to the tube axis and therefore cannot exhibit ferroelectricity. The NTs folded from (0 1 ) layers may show antiferroelectric arrangement of Ti? O bonds. Comparison of stability of the BTO‐based and SrTiO3‐based NTs shows that the former are more stable than the latter. © 2012 Wiley Periodicals, Inc. 相似文献
5.
Perovskites belong to the great group of the inorganic pigments and thanks to their excellent properties they have been widely
used in an industry. CaTiO3, BaTiO3 and SrTiO3 with the perovskite structure were prepared in this work. These compounds were synthesized with using the solid state reaction
by calcination in temperature region 1000–1200°C. The thermal analysis was used for characterization of thermal behaviour
and formation of tested perovskites. The main aim of this work was studied the influence of calcination temperature on colour
properties of perovskites. Colour properties of powdered compounds and samples applied into ceramic transparent glaze P 07491
were also studied. The tested compounds can be described by different light colour hues and that depending on calcining temperature.
The structures of the powdered compounds were studied by X-ray diffraction analysis. 相似文献
6.
High dielectric constant is highly desirable in capacitors and memory devices. In this work, oleic acid (OA)‐capped BaTiO3 nanocrystals were synthesized by a two‐phase approach. Polyimide (PI)/BaTiO3‐nanocrystal composite thin films with high dielectric constant have been successfully fabricated. The morphologies and dielectric properties of the hybrid films were exploited. The results showed that BaTiO3 nanocrystals can be uniformly dispersed in the PI thin films owing to the surface modification of OA‐capped BaTiO3 nanocrystals. It was found that the dielectric constant of composite film varies with the volume fraction of BaTiO3 nanocrystals and sintering temperatures and reaches a maximum value of 44.1, which is around 13 times higher than that of pristine PI thin film (3.2). These results demonstrated that PI/BaTiO3‐nanocrystal composite films have considerable application potential in microelectronic fields. 相似文献
7.
《International journal of quantum chemistry》2018,118(12)
Hydroxylapatite is an important calcium phosphate phase whose knowledge is useful in different fields, for instance in bone biology, development of biomaterials and even cultural heritage. In this work, the equation of state of this mineral was calculated by using the quasi‐harmonic approximation, also including for the first time the temperature effect. In athermal conditions (0 K), we found that the pressure dependence of the hydroxylapatite unit cell volume is well described by a third‐order Birch–Murnaghan formulation, with parameters K0 = 115.9(1), K' = 4.47(6), and V0 = 524.323(27). The inclusion of temperature led to a lower bulk modulus, for example, KT0 = 109.55 GPa at 300 K. The thermal expansion coefficient between 0 and 1000 K was also reported. The results are in good agreement with the few available experimental data reported in literature and further extend the knowledge of the mechanical and thermal behavior of this important mineral. 相似文献
8.
1N‐Phenyl‐3‐(2,4‐dichlorophenyl)‐5‐(4‐chlorophenyl)‐2‐pyrazoline has been synthesized and characterized by elemental analysis, IR, UV‐Vis and X‐ray single crystal diffraction. Density functional calculations have been carried out for the title compound by using the B3LYP method with a 6‐311G** basis set. The calculated results show that the predicted geometry can reproduce well the structural parameters. The electronic absorption spectra calculated in the gas phase are better than those calculated in EtOH solvent to model the experimental electronic spectra. Natural Bond Orbital (NBO) analyses suggest that the above electronic transitions are mainly assigned to π → π* transitions. On the basis of vibrational analyses, the thermodynamic properties of the compound at different temperatures have been calculated, revealing the correlations between C0p, m, S0m, H0m and temperature. 相似文献
9.
Yoichi Yamaguchi 《International journal of quantum chemistry》2011,111(12):3230-3238
Transport properties, temperature‐dependent phonon‐limited electrical and thermal resistivities in the normal state of two‐dimensionally (2D) infinite‐fused zinc porphyrin with a directly meso‐meso‐, β‐β‐, and β‐β‐linked array structure ZnP ∞ were theoretically calculated using linear‐response approach based on density functional theory (DFT). The calculated transport electron–phonon coupling (EPC) constant using the density functional perturbation theory (DFPT) shows almost equal to the superconducting EPC constant, which is the similar situation within a difference by ca. 10% between them for the transition metals. The calculated electrical and thermal resistivities at 300 K obtained by solving the Boltzmann equation within the lowest‐order variational approximation (LOVA) are only larger by one digit than those of the reference metal Al, expecting to become a fantastic 2D synthetic metal without an injection of conductive carriers from outside, e.g., by doping. The calculated results for the 2D infinite‐fused lithium porphyrin LiP ∞ with the same ground state as the one‐electron oxidative state of ZnP ∞ were also discussed for comparison. This simple approach using the first applied plane‐wave ultrasoft pseudopotentials (US‐PPs) is a usable technique for the prediction of the transport properties of simple metallic materials within the practical temperature range. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
10.
BaTiO3/bismaleimide/epoxy/glass fiber reinforced composites were prepared using E-glass fiber (E-GF) and silane coated E-glass fiber (SC-EGF) separately as reinforcement. BaTiO3 nanoparticles were prepared by hydrothermal method. Results show that the addition of BaTiO3 nanoparticles has significant effects on the mechanical and dielectric properties of the composite. Both E-GF and SC-EGF reinforced BaTiO3/bismaleimide/epoxy composites with 2 wt percentages of BaTiO3 nanoparticles showed improved tensile strength, flexural strength and dielectric constant and those with 3% showed high dielectric strength indicating this composition is more adaptable for high voltage insulating applications. Dielectric constants and dielectric loss of the fabricated nanocomposites have been obtained at higher frequencies (in GHz) by using Vector Network Analyser at room temperature and was found to be highest for the BMI-Epoxy nanocomposite with 1% weight nanofiller. 相似文献
11.
Zhongfeng Jia Shengyu Feng Enfeng Song Wenyan Sun Lixiao Cong 《International journal of quantum chemistry》2009,109(2):342-348
The thermal rearrangement mechanisms of 2‐silylethylacetate H3SiCH2CH2OOCCH3 were investigated by ab initio molecular orbital theory for the first time. All structures of reactant, transition states, and products were located and fully optimized at the B3LYP/6‐311+G(d, p) levels, and harmonic vibrational frequencies for the involved stationary points on the potential energy surface were obtained. The reaction pathways were analyzed and confirmed by intrinsic reaction coordinate (IRC) calculations. Furthermore, atomic charges were determined by using the natural bond orbital (NBO) analysis. The calculational results show that H3SiCH2CH2OOCCH3 can rearrange thermally in two ways. One is [1,3] rearrangement (Reaction A), in which silyl group transfers from carbon to oxygen(in C? O? C) via a four‐membered ring transition state, forming silyl acetate and ethylene, the other way, [1,5] rearrangement (Reaction B), happens with transferring of silyl group from carbon to oxygen (in C?O) via a six‐membered ring transition state, forming the same products as in Reaction A. The energy barriers of the Reactions A and B were calculated to be 188.9 and 191.6 kJ/mol at the B3LYP/6‐311+G(d,p) levels, respectively. Changes in thermodynamic functions (ΔS, ΔH, and ΔG), equilibrium constant K(T), as well as preexponential factor A(T), and reaction rate constant k(T) in Eyring transition state theory were calculated over a temperature range of 200–1600 K, and then thermodynamic and kinetic properties of the reactions were analyzed. It can be suggested that Reactions A and B are noncompetitive, and both happen only at elevated temperature. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
12.
《无机化学与普通化学杂志》2018,644(4):253-259
The thermal expansion behavior of Li3AsW7O25 has been studied. The temperature‐dependent development of crystal structural parameters was obtained from Rietveld refinement using neutron time of flight powder diffraction data. Modeling of the lattice thermal expansion was carried out using a Grüneisen first‐order approximation for the zero‐pressure equation of state, where the temperature‐dependent vibrational energy was calculated taking the Debye‐Einstein‐Anharmonicity approach. Temperature‐dependent Raman spectra shed light on some selective modes with unusual anharmonicity. Debye temperatures were calculated using three different theoretical approaches, namely, thermal expansion, mean‐squared isotropic atomic displacement parameter and heat capacity. Similarities as well as discrepancies between the numerical values obtained from different theoretical approaches are discussed. 相似文献
13.
The detailed mechanism of the NO2+CH4 reaction has been computationally investigated at the M06‐2X/MG3S, B3LYP/6‐311G(2d,d,p), and MP2/6‐311+G(2df,p) levels. The direct dynamics calculations were preformed using canonical transition state theory with tunneling correction and scaled generalized normal‐mode frequencies including anharmonic torsion. The calculated results indicate that the NO2+CH4 reaction proceeds by three distinct channels simultaneously, leading to the formation of trans‐HONO (1a), cis‐HONO (1b), and HNO2 (1c), and each channel involves the formation of intermediate having lower energy than the final product. The anti‐Hammond behavior observed in channel 1a is well analyzed. Proper treatment of anharmonic torsions about the C···H···O (or N) axis in the transition structures greatly improves the accuracy of kinetics predictions. The activation energy for each channel increases substantially with temperature, but is not strictly a linear function of temperature. Therefore, the thermal rate constants are fitted to the four‐parameter expression recommended for this case over the wide temperature range 400–4000 K. © 2012 Wiley Periodicals, Inc. 相似文献
14.
The crystal compound [N (CH3)4]2PdCl4 was crystallized in the orthogonal system and the space group is P4/mmm and the refined unit cell parameters are a = b = 8.831 Å, c = 11.415 Å. The structure, vibrational spectra and optical properties have been investigated. DSC studies indicate the presence of two phase transitions at higher temperature which confirm the thermal stability of the palladium-based compound. These transitions have been studied by Raman scattering on single crystals as a function of temperature which confirmed their nature. The assignment of the observed bands is discussed based in the theoretical calculated frequencies by the density functional theory (DFT) method using B3LYP/LanL2DZ basis in the GAUSSIAN-09 package of programs. The optical properties in the UV–visible region have been deduced and the energy gap has been determined which is equal to 3.11 eV. 相似文献
15.
Tozaki K. Masuda R. Matsuda S. Tokitomo C. Hayashi H. Inaba H. Yoshimura Y. Kimura T. 《Journal of Thermal Analysis and Calorimetry》2001,64(1):331-339
A new method to measure heat flux and thermal expansion simultaneously with a temperature resolution of milli-Kelvin is presented
to observe the multistage transitions. At least six thermal anomalies are observed between 402 and 403 K in BaTiO3 simultaneously in heat flux and thermal expansion in the cooling process. The correspondence of the anomalies observed in
the two physical properties is excellent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Mehrnoosh Atashfaraz Mojtaba Shariaty-Niassar Satoshi Ohara Kimitaka Minami Mitsuo Umetsu Takashi Naka Tadafumi Adschiri 《Fluid Phase Equilibria》2007
Fine BaTiO3 nanoparticles were prepared by hydrothermal synthesis under supercritical condition (400 °C and 30 MPa) from mixture of barium hydroxide and titanium dioxide as starting precursors. First, conditions for synthesizing BaTiO3 were examined by using batch reactors. High pH condition, pH > 13, is necessary to obtain phase pure BaTiO3. The reason was discussed based on the solubility of titanium dioxide, which that dissolution–recrystallization process is essential for the synthesis of BaTiO3 nanoparticles. Rapid heating of the starting precursors by mixing with high temperature water in a flow reactor is effective to synthesize smaller size and narrower particle size distribution for the BaTiO3 nanoparticles, compared with the case of slow heating with a batch reactor. 相似文献
17.
Rajendra A. Kalgaonkar Somnath Nandi Sanjeev S. Tambe Jyoti P. Jog 《Journal of Polymer Science.Polymer Physics》2004,42(14):2657-2666
The solid‐state viscoelastic properties are examined for intercalated nanocomposites based on a copolyester and (2‐ethyl‐hexyl)dimethyl hydrogenated‐tallow ammonium montmorillonite. The nanocomposites are prepared via the direct melt intercalation technique using a conventional twin‐screw extruder. Dynamic mechanical thermal analysis of the nanocomposites is conducted using two different test setups. The dynamic mechanical relaxation spectra show an increase in the storage modulus of the nanocomposite over the entire temperature range under study as compared to the pristine polymer (except in the transition region from 70 to 80 °C). These results are analyzed using the empirical Havriliak–Negami (HN) equation. The four temperature independent HN parameters (α, β, E0, and E∞) and one temperature dependent parameter (τ, the relaxation time) are determined by solving the HN equation for each temperature over the range of temperatures. The calculated moduli results fit well with the experimental values of the relaxation spectra for the nanocomposites. This study shows that the HN model can be applied to polymer layered silicate nanocomposites, and it can be used to predict their dynamic mechanical properties over a wide range of temperatures and frequencies a priori. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2657–2666, 2004 相似文献
18.
Silicon-containing polyimide/BaTiO3 nanocomposite films were prepared by the direct mixing of silicon-containing polyamic acid and BaTiO3 nanoparticles under ultrasonic wave irradiation, followed with thermal imidization. Structure and thermal properties were measured with FTIR, XPS, SEM, DSC and TGA. The results showed that the compatibility of BaTiO3 and a polyimide might be improved by the introduction of dimethylsilylene groups into the backbone of a polyimide; and BaTiO3 nanoparticles in the nanocomposites tended to form clusters. The clusters coalesced into a more uniform structure at a higher BaTiO3 filling than at a lower one.The interfacial interaction between BaTiO3 and the silicon-containing polyimide resulted in the increase of the glass transition and the thermal decomposition temperature. It was found that the nanocomposites exhibited lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value was related to the content of BaTiO3 in the nanocomposites. 相似文献
19.
《Journal of Polymer Science.Polymer Physics》2018,56(15):1101-1108
The aim of this study is to improve the dielectric and mechanical properties of HDPE/BaTiO3 composites by binary BaTiO3 particles, when the volume fraction of BaTiO3 is constant. In this study, it was found that the pack density of binary BaTiO3 particles in HDPE/BaTiO3 composite relies on particle ratio and volume fraction of small particles. It is found that the addition of 50 vol % 1600 nm BaTiO3 particles can boost the dielectric constant of HDPE control from 2 to 30 (14 times higher) at 40 Hz and 19 (8.5 times higher) at 40 MHz, respectively. When the particle ratio was 4, the substitution of 10 vol % 1600 nm BaTiO3 particles by 10 vol % 400 nm BaTiO3 particles can further enhance the dielectric constant of HDPE/L‐BT (10/10) from 30 to 50 (67% increase) at 40 Hz and from 19 to 42 (121% increase) at 40 MHz, respectively, without greatly influencing the volume resistivity of HDPE composites. In addition, the thermal conductivity of HDPE with binary BaTiO3 particles were all above 2.0 W/(m•K). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1101–1108 相似文献
20.
Low-temperature heat capacities of octahydrated barium dihydroxide, Ba(OH)2·8H2O(s), were measured by a precision automated adiabatic calorimeter in the temperature range from T=78 to 370 K. An obvious endothermic process took place in the temperature range of 345-356 K. The peak in the heat capacity curve was correspondent to the sum of both the fusion and the first thermal decomposition or dehydration. The experimental molar heat capacifies in the temperature ranges of 78-345 K and 356-369 K were fitted to two polynomials. The peak temperature, molar enthalpy and entropy of the phase change have been determined to be (355.007±0.076) K, (73.506±0.011) kJ·ol^-1 and (207.140±0.074) J·K^-1·mol^-1, respectively, by three series of repeated heat capacity measurements in the temperature region of 298-370 K. The thermodynamic functions, (Hr-H298.15 k )and (Sr-S298.15k), of the compound have been calculated by the numerical integral of the two heat-eapacity polynomials. In addition, DSC and TG-DTG techniques were used for the further study of thermal behavior of the compound. The latent heat of the phase change became into a value larger than that of the normal compound because the melfing process of the compound must be accompanied by the thermal decomposition or dehydration of 71-120. 相似文献