Lattice Vibrational Properties Research Articles

Preparation of highly tunable ZnO/Al2O3-bst50 composite ceramics via defect engineering and composite effect

A series of new x (yZnO/Al2O3)-(1-x)Ba0·5Sr0·5TiO3 (x = 10, 20, 50 wt%, y = 1, 1.3, 1.5 mol) ceramics were prepared by solid-phase method. The effects of ion diffusion and compound effect on the lattice vibration and dielectric properties of Ba0·5Sr0·5TiO3 were studied. When ZnO and Al2O3 are equimolar, the two react to form ZnAl2O4. Under the composite effect, the dielectric permittivity of Ba0·5Sr0·5TiO3 is effectively reduced, Tc moves to high temperature, and the tunability gradually increases. When ZnO is in excess, Tc remains basically unchanged, proving the unique role of the spinel structure. Because ZnO can fully diffuse into Ba0·5Sr0·5TiO3, extremely high tunability is achieved through defect engineering. 50 wt% (ZnO/Al2O3)-50 wt%Ba0·5Sr0·5TiO3 achieved excellent microwave dielectric properties, with dielectric permittivity, tunability and Q value of 201, 23.6 % and 368, respectively. In addition, ZnAl2O4–Ba0.5Sr0·5TiO3 composite ceramics were successfully prepared by directly compounding Ba0·5Sr0·5TiO3 with oxides, which greatly reduced energy loss.

Effects of W6+ on the microstructure, sinterability, lattice vibration, and dielectric properties of Pr2Zr3(Mo1˗xWxO4)9 ceramics at microwave/terahertz/infrared regions

In this article, a series of Pr2Zr3(Mo1−xWxO4)9 ceramics were prepared using the solid-state reaction method and investigated in terms of phase compositions, lattice stress, lattice vibrations, and dielectric properties at microwave, terahertz, and infrared regions. X-ray diffraction (XRD) analysis revealed that all ceramics possess a trigonal structure (R-3c space group) with no discernible second-phase presence. Moreover, the ceramics exhibit oriented growth along the (0,0,18) crystal plane. The densification of all ceramics occurred within the range of 800–825 °C. Raman spectroscopy exhibited a minor blue shift in the predominant peak as the x value increased. The complex permittivity (ε′ and ε″) were evaluated using both infrared reflectance spectrum and terahertz time-domain (THz-TD) spectroscopy. Interestingly, the THz-TD spectral data exhibited a closer agreement with the measured values, which was attributed to a significant relaxation polarization mechanism. Specifically, the peaks below 400 cm−1 contributed significantly to the dielectric parameters, accounting for 88.4% and 95.7% of ε′ and ε″, respectively. As a result of these findings, it is suggested that Pr2Zr3(Mo0.94W0.06O4)9 (εr = 9.82, Qf = 81,892 GHz, τf = −17.90 ppm/°C) ceramics synthesized at 825 °C hold promise as potential materials for high-frequency communication circuits.

AY2Al4GeO12 (A = Ca, Mg) ceramics: Phase composition, microstructure, lattice vibration, bond characteristics, and microwave dielectric properties

In this work, cubic garnet-type AY2Al4GeO12 (A = Ca, Mg) ceramics were synthesized by a solid-state reaction method. XRD detected that CYAG was a single-phase, and the secondary phase existed in the MYAG. SEM, density, and dielectric properties results indicate that the optimum sintering temperature of CYAG and MYAG ceramics is 1550 °C, the CYAG and MYAG ceramics exhibited the best microwave dielectric properties of εr = 8.94, Q×f = 93805 GHz, τf = −48 ppm/°C and εr = 7.06, Q×f = 30549 GHz, τf = −26.55 ppm/°C, respectively. Rietveld refinement, Raman and XPS confirmed that the significant difference in dielectric properties is related to the secondary phase, structural disorder and oxygen vacancy. The relationship between the Q×f and lattice vibration are discussed. τf is explained by oxygen bond valence. The influence of bond characteristics on dielectric properties was analyzed. The reported microwave ceramics are expected to be used as substrate materials in the millimeter wave band.

Computational study on the structural, electronic, lattice vibration, and magnetism in Zn(1−x)FexSeyTe(1−y) quaternary materials

In this article, we studied the structural, electrical, lattice vibrational, and magnetic properties of the quaternary compound Zn(1−x)FexSeyTe(1−y) using density functional theory. All the calculations have been performed based on first-principles calculations using Perdew–Zunger [local-density approximation (LDA)] and Hubbard parameter correction (LDA+U) functionals as employed in the Quantum Espresso package. The computed equilibrium lattice parameter for ZnTe is 6.01 Å, and the energy bandgap, Eg, is 1.362 eV, which is consistent with the experimental values as well as the previous reports, respectively. The influence of the co-doping of iron and selenium on electrical and magnetic properties in a ZnTe system is discussed in detail. The co-doping of iron and selenium affects metallic behavior in these systems by forming localized states between the conduction and valance bands. The presence of localized states is related to the metallic properties of the iron atom, specifically iron 3d orbitals. The spin-polarized density of state and band structure computations also confirmed that the iron and selenium co-doped ZnTe system exhibits significant half-metal ferromagnetic and dilute magnetic semiconductor features at room temperature. Furthermore, the phonon calculation of these systems indicated that the systems are dynamically stable and that localized frequency states are created at higher frequencies due to the presence of iron atoms. As a result, the iron and selenium co-doped ZnTe systems can be considered for magnetic and spintronic device applications at room temperature, pending further experimental research.

Topological data analysis of TEM-based structural features affecting the thermal conductivity of amorphous Ge

Compared to crystalline materials, amorphous materials lack periodicity and exhibit distinct thermal and lattice vibration properties. Hence, analyzing atomic networks in the transmission electron microscopy (TEM) images of amorphous materials is challenging. In this study, we employ topological data analysis (TDA) and principal component analysis (PCA) to extract structural features from the TEM images of amorphous germanium (a-Ge) and analyze its atomic networks. Our findings demonstrate that the thermal conductivity of a-Ge is influenced by larger atomic rings with more vertices, which facilitates the heat transfer through longer atomic chains and results in a higher thermal conductivity. A comparison of the experimental and simulation data confirms the non-random nature of the atomic arrangements in a-Ge. We propose herein an approach that employs the TDA to identify and analyze the atomic networks in amorphous materials, establishing connections to their thermal properties. This study enhances our understanding of amorphous materials and paves a way for tailored material design and engineering to achieve the desired thermal properties.

Many Body Aspects on the Lattice Vibrational Properties of Germanene and Silicene along Highly Symmetry Directions

The investigation of lattice vibrational properties in monolayer two-dimensional honeycomb lattices comprising 2D group-IV semiconductor materials such as Germanene and Silicene (Low Buckled structure) holds immense significance in the realm of research, owing to their potential integration into the forthcoming electronic sector for information technology. The ductile nature of 2D group-IV semiconductor materials enables seamless integration with existing semiconductor technology on substrates, setting them apart from Graphene. Our primary objective revolves around comprehending the lattice vibrational properties of Germanene and Silicene (LB) through the examination of their honeycomb and buckled lattice structures. We use the Adiabatic Bond Charge Model with a Python program to derive vibrational frequencies at the Г points along highly symmetrical directions. Moreover, we extensively analyze the acoustical and optical contributions to the lattice vibrational frequencies. We anticipate that the phonon frequencies along the Г‒M direction for 2D atomically thin Germanene and Silicene will yield reasonably similar outcomes to those other research groups achieve.

The lattice vibration, mechanical anisotropy, stress-strain behavior and electronic properties of ZrxCuySiz intermetallics: A first-principles study

In recent years, ternary metal silicides have attracted more and more interests because of their excellent physical and chemical properties. The mechanical properties, electronic structures and thermal properties of ZrCuSi, ZrCuSi2, Zr3Cu4Si2, Zr3Cu4Si4 and Zr6Cu8Si12 ternary silicide were calculated by first-principles methods. The formation enthalpies, phonon dispersions and single-crystal elastic constants reveal that ZrCuSi, ZrCuSi2, Zr3Cu4Si2, Zr3Cu4Si4 and Zr6Cu8Si12 are thermodynamically, dynamically and mechanically stable. According to the analysis of the enthalpy of formation, ZrCuSi is the most thermodynamically stable intermetallics. Besides, Push's ratio (BH/GH), Poisson's ratio v, hardness and elastic anisotropic were investigated. The results indicated that ZrxCuySiz intermetallics show brittle properties and elastic anisotropy. Cu–Si bonds can be formed in ZrxCuySiz intermetallics due to the strong hybridization between Cu-3d and Si-3s states. The analysis of the electronic properties confirms that ZrxCuySiz intermetallics show the metallic behavior. The stability and mechanical properties are further explained by Debye temperature and electronic properties.

Primitive to conventional geometry projection for efficient phonon transport calculations

The primitive Wigner-Seitz cell and corresponding first Brillouin zone (FBZ) are typically used in calculations of lattice vibrational and transport properties as they contain the smallest number of degrees of freedom and thus have the cheapest computational cost. However, in complex materials, the FBZ can take on irregular shapes where lattice symmetries are not apparent. Thus, conventional cells (with more atoms and regular shapes) are often used to describe materials, though dynamical and transport calculations are more expensive. Here we discuss an efficient anharmonic lattice dynamic method that maps conventional cell dynamics to primitive cell dynamics based on translational symmetries. Such symmetries have not been utilized in typical lattice dynamical calculations. This leads to phase interference conditions that act like conserved quantum numbers and a conservation rule for phonon scattering that is hidden in conventional dynamics which significantly reduces the computational cost. We demonstrate this method for phonon transport in a variety of materials with inputs from first-principles calculations and attribute its efficiency to reduced scattering phase space and fewer summations in scattering matrix element calculations.

Vibrations and Phase Stability in Mixed Valence Antimony Oxide.

α-Sb2O4 (cervantite) and β-Sb2O4 (clinocervantite) are mixed valence compounds with equal proportions of SbIII and SbV as represented in the formula SbIIISbVO4. Their structure and properties can be difficult to calculate owing to the SbIII lone-pair electrons. Here, we present a study of the lattice dynamics and vibrational properties using a combination of inelastic neutron scattering, Mössbauer spectroscopy, nuclear inelastic scattering, and density functional theory (DFT) calculations. DFT calculations that account for lone-pair electrons match the experimental densities of phonon states. Mössbauer spectroscopy reveals the β phase to be significantly harder than the α phase. Calculations with O vacancies reveal the possibility for nonstoichiometric proportions of SbIII and SbV in both phases. An open question is what drives the stability of the α phase over the β phase, as the latter shows pronounced kinetic stability and lower symmetry despite being in the high-temperature phase. Since the vibrational entropy difference is small, it is unlikely to stabilize the α phase. Our results suggest that the α phase is more stable only because the material is not fully stoichiometric.

Lattice vibration and dielectric properties of CaNb2O6

The lattice vibration and dielectric properties of CaNb2O6 have been studied using density functional perturbation theory. The complete set of the zone center optical phonon modes and frequency dependent dielectric function of the CaNb2O6 have been determined. The assignment of mode vibrations to all of the optical phonon frequencies was made by analyzing the eigen displacements. We find that the highest frequency mode of all the Raman active symmetry species is due to NbO6 stretching vibration. Our calculated dielectric functions and quality factor are in very good agreement with the corresponding experimental results.

Lattice Vibration, Optical and Mechanical Properties of AlP Semiconductor under the Influence of Pressure

The lattice vibrations, optical, and mechanical properties of zinc-blende AlP semiconductor have been investigated. Research has been carried out to determine how pressure affects various properties, including the refractive index, optical and static dielectric constants, longitudinal and transverse sound velocities, reflectivity, susceptibility, phonon frequencies, ionicity, transverse effective charge, and micro-hardness. The pseudo-potential method (EPM) was used to perform the computations in this article. A fair degree of agreement is seen when comparisons are made with the available experiment and other theoretical calculations.

First-principles study on the lattice vibration, anisotropy, tensile strength and electronic properties of CuxHfySiz intermetallics

The stability, lattice vibrations, anisotropy in elasticity and stress–strain behavior of the CuxHfySiz ternary silicide were calculated by first-principles methods. According to the formation enthalpy and lattice vibration frequency, the CuxHfySiz phase is confirmed to be stable. The elastic constants show that these ternary borides are mechanically stable. Based on the BH/GH rule, CuHfSi is 1.788 and more significant than 1.75, which should be ductile. The elastic hardness indicates that CuHfSi2 shows the largest hardness among CuxHfySiz phases, which is 18.9 GPa. It is speculated that CuHfSi2 may be the most muscular hardness in these four types of intermetallics. The size of anisotropy expressed by anisotropy and elastic modulus three-dimensional diagram is Cu4Hf3Si4 > Cu4Hf3Si2 > CuHfSi > CuHfSi2. The structural stability, hardness and chemical bonds were further explained by electronic structures.

Vibrational and dielectric properties of InN in orthorhombic Pnma phase

We have determined the lattice vibrational and dielectric properties of the newly predicted orthorhombic Pnma-InN, using the density functional perturbation theory. The origin of the observed phonon band gap separating optical modes is discussed. The full set zone center phonon modes and the longitudinal-transverse (LO-TO) splitting are presented and discussed. The LO-TO splitting is found to be largest for B2u mode at 471.33 cm−1 which is dominated by in-phase displacements of nitrogen atoms. The structural and dielectric properties of the orthorhombic Pnma-InN are compared to those of wurtzite and zinc blende phases of InN.

Lattice vibration, optical, and mechanical properties of aluminum phosphide (AlP) compound under the influence of temperature

Lattice vibration, optical, and mechanical properties of aluminum phosphide (AlP) compound under the influence of temperature

Development of a machine-learning interatomic potential for uranium under the moment tensor potential framework

Uranium is attracting growing interest across fundamental science and nuclear research, where atomistic simulations remain challenging. In this study, we developed a novel uranium interatomic potential based on a machine-learning approach embedded in the moment tensor potential package. An active learning framework was utilized in the potential training, using density-functional theory plus Hubbard U (DFT+U) modified data. The potential accurately reproduced the lattice parameters, cohesive energy, elastic, vibrational, and thermodynamic properties of α-U compared to DFT+U calculations and experimental results. The basic properties of other phases, including β, γ, HCP, and FCC phases, were also validated. In addition, molecular dynamics simulations were used to reproduce the temperature-induced allotropic transformation from α-U to γ-U, which agrees with experimental observations. Our potential provides a computationally efficient means to study the physical behavior of uranium with nearly DFT accuracy.

Nanoarhitectonics of Inorganic-Organic Silica-Benzil Composites: Synthesis, Nanocrystal Morphology and Micro-Raman Analysis.

The synthesis of nanosized organic benzil (C6H5CO)2 crystals within the mesoporous SiO2 host matrix was investigated via X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and ab initio lattice dynamics analysis. Combining these methods, we have proved that the main structural properties of benzil nanocrystals embedded into SiO2 host membranes with pore diameters of 6.0, 7.8, 9.4, and 13.0 nm are preserved compared to a bulk benzil crystal. Space confinement has an insignificant impact on the lattice vibrational properties of benzil crystals implanted into the host matrices. The ab initio lattice dynamics calculation of the phonon spectrum in the Brillouin zone center shows the mechanical and dynamical stability of benzil lattice, revealing very low optical frequency of 11 cm-1 at point Γ.

Thermal transport characteristics of diamond under stress

Diamond exhibits extremely high hardness and thermal conductivity, which makes it widely used in industrial fields such as diamond cutting tools and piezoelectric materials. At the same time, during the diamond applications, the internal characteristics and thermal transport properties of diamond will change under high stress, which has an important impact on its service life and device accuracy. However, the internal properties and thermal transport response of diamond under high stress have not been systematically studied. This paper employed first-principles software to investigate the reaction of the diamond lattice structure, electronic properties, lattice vibration properties, thermodynamic properties, lattice thermal conductivity, phonon group velocity, and phonon free path when subjected to uniaxial compressive stress, shear stress, and hydrostatic pressure. The results show that at a stress of 120 GPa, the response of diamond exhibited distinct anisotropic properties in three kinds of stress states. Changes occur in the position of the carbon atoms, CC bond length, and CC bond angle within the diamond structure when subject to the three kinds of stress fields. The main reason for the above phenomenon is that the stress caused the redistribution of charges around the C atoms in the diamond. Furthermore, the symmetry of the diamond crystal was broken, and the diamond lattice vibration properties undergone alteration, leading to a state of dynamic instability. The thermodynamic properties and phonon group characteristics of diamond changed, and the lattice thermal conductivity of diamond is 2380, 99, and 806 W·m-1K-1, respectively. This theoretical study offers valuable insights into the impact of stress fields on the heat transfer properties of diamonds, providing practical guidance for their use in high-stress environments.

Effects of Li substitution on the sintering behavior, lattice vibration, bond covalence and dielectric properties of SrMgGe2O6 ceramics

Effects of Li substitution on the sintering behavior, lattice vibration, bond covalence and dielectric properties of SrMgGe2O6 ceramics

Thermodynamic and thermoelectric properties of FeCrTiZ (Z = Si, Ge) quaternary Heusler compounds

The objective of this work is to find the possible applications of the compounds as thermoelectric materials or alternate energy materials. In this regard, FeCrTiZ (Z = Si, Ge) quaternary Heusler compounds have been analyzed via investigating their stable structure and other physical properties by using comprehensive density functional theory executed in the WIEN2k package. The optimized lattice constants and other ground state parameters are found to be concurrent with the existing data. The spin-embraced electronic properties lead to the half-metallic character of the compounds on account of different behavior of the two spins. The obtained total magnetic moment ideally follows the Pauling-Slater rule and is also congruent to the available data. Furthermore, to study the lattice vibrational properties, the dependence of unit cell volume, bulk modulus, Debye temperature, and Gruneisen constant has been estimated within a certain temperature and pressure range by employing a Debye model of quasi-harmonic approximation. The thermoelectric parameters have also been estimated by employing the BoltzTrap code which gives significant values of the figure of merit for both compounds.

Microwave dielectric properties of ternary molybdate NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics for LTCC applications

Two kinds of scheelite-structure microwave dielectric ceramics with I41/a space group were prepared by the conventional solid-phase reaction method. The effects of different sintering temperatures on the crystal structure, lattice vibration and microwave dielectric properties of NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics were investigated. XRD and Rietveld refinement results show that NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics belong to tetragonal scheelite structure with I41/a space group. The lattice vibration mode was analyzed by Raman spectroscopy, and the correlation between the dielectric performances and structure was established. The NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics have high density (>97%) and excellent microwave dielectric properties of εr = 10.47, Qf = 38951 GHz, τf = −48.43 ppm/°C for NaSrNd(MoO4)3 sintered at 775 °C and εr = 9.55, Qf = 41081 GHz, τf = −44.92 ppm/°C for NaSrSm(MoO4)3 sintered at 800 °C. In addition, NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics have excellent chemical compatibility with Ag electrodes, which means that the ceramic could be used in LTCC microwave devices.