Evolution Of Lattice Structure Research Articles

High temperature lattice structure evolution of C-axis preferred orientation AlN thin films and its application in temperature measurement

In order to measure the surface temperature of aerospace hot-end components accurately, AlN thin film temperature measurement technology was explored. In this research, C-axis preferred orientation AlN thin film was deposited on Ni-based superalloy substrates by medium frequency (MF) reaction magnetron sputtering. Effect of temperature on the lattice structure of AlN thin film was studied. X-ray diffraction results show that the diffraction angles (2 θ ) of AlN thin films shift to the left side monotonously with the increase of annealing temperature and annealing time. Based on this phenomenon, the maximum temperature experienced by the film can be deduced according to 2 θ values. A temperature interpretation algorithm equation was established with MATLAB. The algorithm is a binary linear equation, whose dependent variable is 2 θ and the independent variables are annealing temperature and annealing time. Then, temperature interpretation software was developed with Visual Studio 2019. The temperature interpretation range is 700–1200 °C and the relative interpretation error is less than 4.26%.

Structural evolution and bandgap modulation of layered β-GeSe2 single crystal under high pressure

Germanium diselenide (GeSe2) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of β-GeSe2 at high pressure is still uncertain. Here we prepared high-quality β-GeSe2 single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of β-GeSe2 under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of β-GeSe2 turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of β-GeSe2 reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of β-GeSe2 and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material.

Effect of lattice structure evolution and stacking fault energy on the properties of Cu–ZrO2/GNP nanocomposites

A hybrid nanocomposite comprising nanosized ZrO2 and graphene nanoplatelet (GNP)-reinforced Cu matrix was synthesised via powder metallurgy. The influence of sintering temperature and GNP content on the electrical and mechanical behaviour of the Cu–ZrO2/GNP nanocomposite was investigated. The ZrO2 concentration was fixed at 10% for all the composites. Upon increasing the GNP concentration up to 0.5%, a significant improvement was observed in the compressive strength, microhardness, and electrical conductivity of the composite. Furthermore, the properties were significantly improved by increasing the sintering temperature from 900 to 1000 °C. The compressive strength, hardness, and electrical conductivity of Cu–10%ZrO2/0.5%GNP were higher than those of the Cu–ZrO2 nanocomposite by 60, 21, and 23.8%, respectively. This improvement in the mechanical properties is because of the decrease in the crystallite size and dislocation spacing, which increases the dislocation density, thereby increasing the impedance towards dislocation movement. The lower stacking fault energy of the hybrid nanocomposites enables easier electron transfer within and between the Cu grains, resulting in an improved electrical conductivity. The enhancement in strength and electrical conductivity were aided by the GNPs and ZrO2 nanoparticles that were dispersed widely in the Cu matrix.

Effect of lattice structure evolution on the thermal and mechanical properties of Cu–Al2O3/GNPs nanocomposites

In this study, high-energy ball milling accompanied by compaction and sintering were employed for manufacturing Cu-based hybrid nanocomposite reinforced by Al2O3 and GNPs. This hybrid nanocomposite is proposed to meet the specification of heat sink applications, where excellent mechanical and thermal performance is demanding. Different processing parameters were experimentally considered such as sintering temperature and weight percentage of GNPs, 0, 0.25, 0.50, 0.75, and 1 wt %. The weight percentage of Al2O3 was fixed at 10%. The results demonstrated that the mechanical and thermal performance of the fabricated nanocomposites were superior for nanocomposite containing 0.5% GNPs and sintered at 1000 °C. The hardness, the thermal conductivity and the coefficient of thermal expansion (CTE) were improved by 21%, 16.7%, and 55.2%, respectively, compared to composite without GNPs addition. The improved mechanical and thermal properties were attributed to the low stacking fault energy, small crystallite size, high dislocation density, and low lattice strain of the composite prepared at this composition. Moreover, the better dispersion of the nano-particles of GNPs and Al2O3 inside the matrix helped for the strength and thermal conductivity improvement while maintaining low CTE.

Evolution of microstructure, defect, optoelectronic and magnetic properties of Cu1-xCaxFeO2 ceramics

Microstructures, defect characteristics, optoelectronic, and magnetic properties of polycrystalline delafossite Cu1-xCaxFeO2 (x = 0.00–0.08) samples have been systemically investigated. Our investigation results distinctly show that divalent Ca2+ ions can successfully substitute partial Cu+ ions and prompt the grain size and induce the partial Fe3+ valence variation to Fe2+. The positron annihilation lifetime spectra signifies that the cation vacancy clusters exist in all samples, the size and concentration of vacancy defects are redistributed with increasing Ca2+ ions content, while the overall defect environment of CuFeO2 system is not changed. The Hall-effect measurement results indicate the transition of semiconductor type from p-type to n-type. The UV–Visible absorption spectroscopy results indicate that the calculated band gap of the prepared samples is estimated to be 3.42–3.58 eV, indicating the series can be applied to the transparent conductive oxide materials. The magnetic measurements reveal that the transition temperature TN1 and TN2 are independent of Ca2+ content x, while the coexistence of antiferromagnetism and weak ferromagnetism for all the doped samples are observed. A moderate Ca2+ content, i.e. x = 0.02, can distinctly promote weak ferromagnetism. The above internal mechanism is probably relevant to the evolution of lattice structure and defect characteristics caused by Ca2+ ions doping.

The S-content-dependent lattice structure evolution and bandgap modulation in quaternary MgZnOS alloy films

Bandgap engineering of ZnO by alloy formation is of great importance for its application in modern optoelectronic devices. Herein, Mg and S co-substituted quaternary Mg0.12Zn0.88O1−y S y (MgZnOS) alloy films with various S content were grown on c-plane sapphire by pulsed laser deposition using a Mg0.12Zn0.88O0.18S0.82 ceramic target under various O2 partial pressures. The S-content-dependent phase structure evolution and S solubility limits in single-phase MgZnOS alloys were determined, and the correlation of lattice constants and band gap with the S content of the single-phase MgZnOS was quantitatively established. It turns out that the MgZnOS films grow quasi-epitaxially on c-sapphire with a wurtzite structure, which evolves intricately with varying S content. The S-rich MgZnOS films assume both lattice constants and in-plane orientation similar to those of ZnS. With decreasing S content, the alloy lattice first contracts along the out-of-plane direction, then shrinks in-plane, and partly re-orients by 30° in-plane, eventually approaching ZnO for the O-rich MgZnOS films. S content (y S) achieved in the single-phase O-rich and S-rich Mg0.12Zn0.88O1−y S y films is y S ⩽ 0.33 and y S ⩾ 0.67, respectively, far beyond the S solubility limits in the counterpart ternary ZnOS. While phase separation of MgZnO and MgZnS takes place in the films with S content between 0.34–0.65, in-plane domain separation with mutual rotation by 30° occurs in the O-rich single-phase MgZnOS films with y S ⩽ 0.08. Moreover, for the O-rich single-phase MgZnOS films, the lattice constant c expands linearly while a remains almost invariant with increasing S content. The band gap of MgZnOS is nonlinearly adjustable in the range of 3.13–3.66 eV, with a bowing parameter (∼1.89 eV) smaller than that of ZnOS (∼3.0 eV). The S-content-dependent evolutions of both lattice constants and band gap of MgZnOS differ distinctly from those of ZnOS, indicating bright prospects for synergistic Mg and S co-substitution in the effective modulation of both structure and band gap of ZnO to meet specific applications.

Reversible synthesis of GO: Role of differential bond structure transformation in fine-tuning photodetector response

The controlled modification of graphene’s electronic band structure poses serious challenges. In the present work, we study the effect of sp 2 cluster size variation on the electronic band gap and photoconductive properties of reduced graphene oxide (RGO). This is achieved by performing reversible functionalization of RGO with oxygen species. The reversible functionalization of RGO results in its partial transformation to graphene oxide (GO) so that the size of the sp 2 clusters within the sp 3 matrix varies, thereby affecting the π-π* band structure and photoconductive properties. The study reveals: (1) incremental creation/elimination of oxygenated surface bonds’ related energy states within the π-π* band; (2) customized tuning of the sp 2/sp 3 ratio; (3) the presence/absence of oxygenated states impacts the optical transition processes both from band-to-band and oxygenated states; and (4) the incremental addition/depletion of surface states in a tunable manner directly influences the carrier transport in the photoconductive device. Experiments show a two-stage transformation of RGO electronic properties with changing oxygen functionalities: oxidation (Stage I) and decomposition or erosion (Stage II). Sp 2 cluster size variation induced bandgap change was analyzed by Raman and photoluminescence studies, indicating the possibility for photodetection in a specific band encompassing NIR to UV, depending on the sp 2/sp 3 ratio. Energy-dispersive x-ray spectroscopy and Fourier transform infrared studies confirm the surface oxygenation/de-oxygenation during plasma treatment, and XRD confirms partial transformation of RGO to GO and its amorphization at higher plasma exposure times. In addition, the photodetector performance is optimized in terms of carrier generation-recombination and carrier-lattice scattering. Thus, manipulating better photoconductive response is possible through suitable handling of the parameters involved in the plasma treatment process. This is the first study on the influence of the sp 2/sp 3 ratio-induced lattice structure evolution on photodetection.

120 MeV Ni10+ swift heavy ions irradiation on CdSe nanocrystals induces cubic to hexagonal phase transformation - A study of microstructural modification

In the present work, chemically synthesized cadmium selenide (CdSe) nanocrystals, which have a cubic lattice structure as per X-ray diffraction (XRD) analysis, has been irradiated with 120 MeV Ni10+ swift heavy ions (SHI) for the study of their structural modification. A significant change in the lattice structure has been found with different ion fluence of 120 MeV Ni10+ irradiation, which may be due to the high electronic energy loss of SHI. AFM analysis also shows changes in morphological properties with ion irradiation. The evolution of lattice structure with different fluence has been studied using double ion impact model. Further, SHI induced cubic to hexagonal transformation effect the microstructural parameters such as intrinsic strain, dislocation density of CdSe nanocrystals. SHI induced microstructural modifications have also been studied with the help of Variance model.

Influence of Al3+ dopant on structure and infrared emission properties of Er3+:Ca3NbGa3Si2O14 crystalline powder

A series of 1.0 at.% Er3+ doped Ca3Nb(Ga1-xAlx)3Si2O14 (CNGAS) powders with different Al3+ content (x = 0–0.7) were prepared through high-temperature solid-state reaction. The effect of replacing Ga3+ by Al3+ on the lattice structure evolution and the emission transition 4I13/2 → 4I15/2 of Er3+ were investigated in detail based on the X-ray powder diffractions, Rietveld refinements, fluorescence spectra and decay curves. It reveals that the Al3+ content in the range of 0–0.5 has little impact on structural integrity and degree of order of the Ca3NbGa3Si2O14 (CNGS) lattice, The Er3+:CNGAS with Al3+ substitution (x = 0.5) exhibits even enhanced fluorescence emission rather than that of the Er3+:CNGS. The results indicates that the strategy of Al3+ substitution is cost-saving and feasible, and Er3+ activated Ca3Nb(Ga0.5Al0.5)3Si2O14 crystal as a promising 1.55 μm laser gain medium would be comparable to that of the CNGS crystal.

Pressure-modulated lattice structural evolution in multilayer ZrS3

Recently, ZrS3, a group IV transition—metal trichalcogenides has attracted much attention due to its light—emission properties. Pressure engineering can effectively modify the photoelectric properties of crystals by tuning their atomic displacement. However, pressure-induced phase transitions in multilayer ZrS3 have not been fully elucidated. This work investigated the lattice structural evolution in compressed multilayer ZrS3 through high-pressure Raman spectroscopy and first-principle calculations. The lattice distorted at 2.5 GPa, as evidenced by a split of Raman mode I. Further compression led to a phase transition at 10.8 GPa, which was related to the rearrangement of dangling S–S pairs along the a-axis. Our study provides a foundation for exploring the potential of pseudo-1D material systems for applications such as electrical and thermal transport, and luminous performance.

Fatigue mechanisms of wheel rim steel under off-axis loading

High-speed railway wheels often experience harsh cyclic loadings in service. To date, plenty of works have been performed to investigate the on-axis high cycle fatigue (HCF) behavior of high-speed railway wheel rim steel. However, the effect of off-axis loading on the HCF behavior is generally not discussed in literature. In this work, a self-designed multi-axis fatigue test fixture was used to realize biaxial tension-bending/shear fatigue loading in the direction of 30° to the axis. For comparison, the on-axis HCF behavior is studied experimentally as well. Based on multiaxial mechanics analysis, a new composite elastic-plastic model for off-axis fatigue was presented. Under almost the same life, although the difference in equivalent stress was not significant between on-axis and off-axis fatigue, experiments found that there were some clear distinct damage mechanisms behind the two fatigue modes in different stress dimensions. Combining with fatigue tests, evolutionary characteristics of macro fracture surface deflection, micro fracture morphology, crack propagation path, dislocation and lattice microstructure beneath fracture critical region were analyzed in depth to make connections with each other, and it was vitally affected by lattice structural evolution, sub-/grains reconstruction, slips shearing at boundaries, and fracture toughness in various degrees. The present research would help us to better understand the law of micro-damage and its evolution of wheel steels under off-axis fatigue.

Electron Transfer Governed Crystal Transformation of Tungsten Trioxide upon Li Ions Intercalation.

Reversible insertion/extraction of foreign ions into/from a host lattice constitutes the fundamental operating principle of rechargeable battery and electrochromic materials. The insertion of foreign ions is a far more commonly observed structural evolution of the host lattice, and for the most cases such a lattice evolution is subtle. However, it has not been clear what factors control such a lattice structural evolution. Based on the tungsten trioxide (WO3) model crystal, we use in situ transmission electron microscopy (TEM) combined with density functional theory calculations to explore the nature of Li ions intercalation induced crystal symmetry evolution of WO3. We discovered that Li insertion into the octahedral cavity of the WO3 lattice will lead to a low to high symmetry transition, featuring a sequential monoclinic → tetragonal → cubic phase transition. The density functional theory results reveal that the phase transition is essentially governed by the electron transfer from Li to the WO6 octahedrons, which effectively leads to the weakening the W-O bond and modifies system band structure, resulting in an insulator-to-metal transition. The observation of the electronic effect on crystal symmetry and conductivity is significant, providing deep insights on the intercalation reactions in secondary rechargeable ion batteries and the approach for tailoring the functionalities of material based on insertion of ions in the lattice.

Vanadium doped Sb2Te3 material with modified crystallization mechanism for phase-change memory application

In this paper, V0.21Sb2Te3 (VST) has been proposed for phase-change memory applications. With vanadium incorporating, VST has better thermal stability than Sb2Te3 and can maintain in amorphous phase at room temperature. Two resistance steps were observed in temperature dependent resistance measurements. By real-time observing the temperature dependent lattice structure evolution, VST presents as a homogenous phase throughout the whole thermal process. Combining Hall measurement and transmission electron microscopy results, we can ascribe the two resistance steps to the unique crystallization mechanism of VST material. Then, the amorphous thermal stability enhancement can also be rooted in the suppression of the fast growth crystallization mechanism. Furthermore, the applicability of VST is demonstrated by resistance-voltage measurement, and the phase transition of VST can be triggered by a 15 ns electric pulse. In addition, endurance up to 2.7×104 cycles makes VST a promising candidate for phase-change memory applications.

Effect of lattice defects on thermal conductivity of Ti-doped, Y2O3-stabilized ZrO2

The evolution of lattice structure and thermal conductivity has been studied systematically for a range of Ti-doped, Y2O3-stabilized ZrO2 (YSZ) solid solutions. The mechanism of reducing the thermal conductivity by Ti doping has been determined. Ti4+ mainly substitutes for Zr4+ below a critical composition factor (x⩽0.08), above which the interstitial Ti4+ need to be considered separately. The effect of lattice defects caused by mass and radius differences between Ti4+ and Zr4+ ions on the phonon scattering coefficient was discussed quantitatively. And the reduction of oxygen vacancy by interstitial Ti4+ ions which increases the thermal conductivity at high Ti doping content was also determined. Concerning the integrated phase stability and thermo-mechanical properties, Ti-doped YSZ is believed to be a promising candidate for thermal barrier coatings at higher temperature.

Structure and dynamics of pentacene on SiO2: From monolayer to bulk structure

We have used confocal micro Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction (XRD) to investigate pentacene films obtained by vacuum deposition on SiO${}_{2}$ substrates. These methods allow us to follow the evolution of lattice structure, vibrational dynamics, and crystal morphology during the growth from monolayer, to TF, and, finally, to bulk crystal. The Raman measurements, supported by the AFM and XRD data, indicate that the film morphology depends on the deposition rate. High deposition rates yield two-dimensional nucleation and quasi-layer-by-layer growth of the T-F form only. Low rates yield three-dimensional nucleation and growth, with phase mixing occurring in sufficiently thick films, where the T-F form is accompanied by the ``high-temperature'' bulk phase. Our general findings are consistent with those of previous work. However, the Raman measurements, supported by lattice dynamics calculations, provide additional insight into the nature of the TFs, showing that their characteristic spectra originate from a loss of dynamical correlation between adjacent layers.

In Situ Characterization of Lattice Structure Evolution during Phase Transformation of Zr‐2.5Nb

AbstractThe α–β phase transformation behavior of Zr‐2.5Nb (in mass%) has been characterized in real time during an in situ neutron diffraction experiment. The Zr‐2.5Nb material in the current study consists, at room temperature, of α‐Zr phase (hcp) and two β phases (bcc), a Nb rich β‐Nb phase and retained, Zr rich, β‐Zr(Nb) phase. It is suggested that this is related to a quench off the equilibrium solubility of Nb atoms in the Zr bcc unit cells. Vegard's law combined with thermal expansion is applied to calculate the composition of the β‐phase, which is compared with the phase diagram, revealing the system's kinetic behavior for approaching equilibrium.

The application of inverse Broyden’s algorithm for modeling of crack growth in iron crystals

In the present paper we demonstrate the use of inverse Broyden's algorithm (IBA) in the simulation of fracture in single iron crystals. The iron crystal structure is treated as a truss system, while the forces between the atoms situated at the nodes are defined by modified Morse inter-atomic potentials. The evolution of lattice structure is interpreted as a sequence of equilibrium states corresponding to the history of applied load/deformation, where each equilibrium state is found using an iterative procedure based on IBA. The results presented demonstrate the success of applying the IBA technique for modeling the mechanisms of elastic, plastic and fracture behavior of single iron crystals.

In-situ size control and structural characterization of barium titanate nanocrystal prepared by crystallization of amorphous phase

We examined the influence of nanocrystalline particle size on the cubic-to-tetragonal phase transition of barium titanate (BaTiO 3). In-situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used in combination with electron microscopy to study the evolution of lattice structure and phase-transformation behavior with heat treatment and particle growth for BaTiO 3. The lattice constants were obtained for various polycrystal orientations in the diameter size range 10–90 nm. In-situ XRD results during the crystallization of amorphous 4BaTiO 3-SiO 2 revealed a critical size of ∼25 nm for the cubic-to-tetragonal phase transition of BaTiO 3 at room temperature.

Crystal structure and orthorhombic–tetragonal phase transition of nanoscale (Li 0.06Na 0.47K 0.47)NbO 3

Lead-free nano (Li 0.06Na 0.47K 0.47)NbO 3 powders, with pure perovskite structure and various grain sizes between about 30 and 60 nm, have been successfully synthesized by a novel sol–gel method, in which Nb 2O 5 was used as the Nb source. The refining XRD and Raman spectra were used in combination with TEM to investigate the evolution of lattice structure and phase transformation behavior as a function of grain size. The results demonstrated that the growth process of grains has been divided into two stages, and the distortion of unit cell apparently decreases with decreasing grain size. At around 35 nm, the phase structure of (Li 0.06Na 0.47K 0.47)NbO 3 changed from orthorhombic to tetragonal. This phenomenon is related to a grain size-induced structural phase transition. For the well accepted wisdom that niobates get super piezoelectric properties in orthorhombic–tetragonal transition region, our results suggested a critical size for the application of (Li 0.06Na 0.47K 0.47)NbO 3 in nano piezoelectric devices.

Processing, Microstructure and Properties of Nanograin Barium Titanate Ceramics by Spark Plasma Sintering

Bulk dense nanocrystalline BaTiO3 ceramics ranging from 15 nm to 100 nm have been successfully prepared by the spark plasma sintering method. Raman spectra and X-ray diffraction were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with grain growth from nanoscale to micrometre scale for BaTiO3 ceramics. Scanning nonlinear dielectric microscopy measurements revealed temperature-dependent variations in contrast, which were attributed to domain rearrangements in BaTiO3 ceramics below 100 nm. Furthermore the piezoresponse hysteresis loops showed that the nanocrystalline BaTiO3 ceramics were switchable and ferroelectricity was retained at the high temperature of 290 oC, demonstrating the existence of nano ferroelectric domains and the ferroelectric phase still retained above Curie temperature, which confirmed the diffused phase transition character in nanograin BaTiO3 ceramics. The dielectric data also show a ferroelectric to paraelectric phase transition in nanograin BaTiO3 ceramics.