Reduction In Lattice Parameter Research Articles

Structure, microstructure, ferroelectric/electromechanical properties and retention characteristics of [Bi1−x Nb x ]FeO3 thin films

In this work, we report the structure, microstructure, ferroelectric/electromechanical properties, and retention characteristics of [Bi1−xNbx]FeO3 (BNFO) thin films [x=0,0.025,0.05, and 0.1] prepared by the polymeric precursor method. X-ray patterns analyses and Rietveld refinement data confirmed that BNFO thin films have a rhombohedral structure and can be obtained at 773 K for 2 h in static air. However, a small quantity of deleterious phase related to Bi2Fe4O9 was observed with the addition of niobium (Nb). Structural refinement data indicated that the substitution of bismuth (Bi) by Nb in the A-site leads to a reduction in lattice parameters and the unit cell volume. Supercell models representing the [BiO6],[NbO6], and [FeO6] clusters which are present in the rhombohedral lattice are shown here. Atomic force microscopy images showed a reduction in the average grain size of films with the substitution of Bi by Nb. Ferroelectric and electromechanical properties were confirmed by hysteresis loops and piezoresponse force microscopy. Ferroelectric/electromechanical properties and retention characteristics indicated that the BNFO films with x=0.1 have a large remnant polarization, a low coercive field, a piezoelectric coefficient (d33≈38 pm/V), and good retention resistance.

Role of beryllium doping in strain changes in II-type InAs/GaSb superlattice investigated by high resolution X-ray diffraction method

We have studied the influence of the beryllium doping on strain in the II-type InAs/GaSb superlattices (SLs) by means of high-resolution X-ray diffraction (HRXRD). Three analyzed superlattices were grown by molecular beam epitaxy. One of the examined superlattices was undoped. Two others structures, called doped SLs, composed of two superlattices: Be-doped and undoped which were grown one on the top of each other. The doping concentration was determined by secondary ion mass spectroscopy. The doping level was 1×1017 cm−3 and 2×1019 cm−3. For doped superlattices, the HRXRD measurements showed splitting of satellite (ST) peaks. Furthermore, the separation of ST peaks increase with doping level. In contrast, for undoped superlattice, the splitting of the ST peaks was not observed. Sometimes the separation of ST peaks can be caused by change of thickness period of superlattice or partial relaxation of the structure. However, we claim that in our experiment the splitting is caused by another mechanism: The presence of Be atoms in SL causes the change of average lattice constant of the superlattice. The influence of Be dopant on lattice parameter of superlattice was confirmed by theoretical simulations. Furthermore, the change of the lattice constant (Δa/a) of the GaSb:Be buffer was examined. The reduction of lattice parameter of GaSb was noticed. It was caused by the presence of Be doping and unintentionally incorporated As-atoms in the GaSb layer. It is very important to know that even very small Be concentration (1×1017 cm−3) causes the change of average lattice parameter of SL.

Observation of high pressure o-GeTe phase at ambient pressure in Si-Te-Ge glasses

Te-rich Si15Te85-xGex (1 ≤ x ≤ 11) glasses are found to exhibit an anomalous phase separations with germanium composition. The structural transformation of o-GeTe crystalline phase from o-GeTe with a = 11.76 Å, b = 16.59 Å, c = 17.44 Å, to high pressure o-GeTe with a new reduced lattice parameters a = 10.95 Å, b = 4.03 Å, c = 4.45 Å, is observed at Tc3 in the composition range 6 ≤ x ≤ 11. Raman studies support the possible existence of high pressure o-GeTe phase which is observed in X-ray diffraction experiments.

Improved High‐Q Microwave Dielectric Ceramics in CuO‐Doped BaTi4O9–BaZn2Ti4O11 System

To improve the microwave dielectric properties, CuO was doped into composite ceramics BaTi4O9–BaZn2Ti4O11 by the solid‐state reaction. CuO worked as flux former and caused the liquid‐phase sintering mechanism, which effectively improved the densification process and lowered the sintering temperature by nearly 100°C. Moreover, Cu2+ substituted for Zn2+ sites in BaZn2Ti4O11 phase, which led to the increase of BaZn2Ti4O11 phase and the reduction of lattice parameters of BaZn2Ti4O11 phase, and both these two results had the positive effect on the dielectric properties, especially the Q × f value. As increasing CuO content from 0.0 to 3.0 wt%, the dielectric constant (εr) increased from 35.5 to 36.5, the Q × f value increased first from 49 100 GHz to the peak value 62 600 GHz (1.0 wt% CuO) and thereafter decreased to 31 900 GHz, and the temperature coefficient of resonant frequency (τf) kept in a low value as <2.0 wt% CuO was added. At last, 0.85BaTi4O9–0.15BaZn2Ti4O11 ceramics with 1.0 wt% CuO sintered at 1150°C for 3 h showed excellent microwave dielectric properties: the high εr = 36.4, the high Q × f= 62 600 GHz and the near‐zero τf = +0.2 ppm/°C.

Atomic Layer Deposition of Al-doped ZnO Films: Effect of Grain Orientation on Conductivity

Al-doped ZnO (AZO) films were deposited by atomic layer deposition (ALD) on borosilicate glass and sapphire(0001) substrates. The Al composition of the films was varied from 1% to 4% by controlling the ratio of Zn:Al pulses. Film resistivity was measured as a function of Al content and the substrate temperature used for ALD deposition. X-ray diffraction (XRD) was performed on the films, showing a reduction in lattice parameter, as a function of Al concentration, indicating that Al3+ ions occupy substitutional sites in the ZnO lattice. The resistivity of films deposited on sapphire substrates (7.7 × 10−4 Ω cm) was lower than that on glass (3.0 × 10−3 Ω cm), because of the formation of textured grains with the c-axis aligned with respect to the sapphire surface, as confirmed by XRD. The surface morphology of the films on glass and sapphire was compared using scanning tunneling microscopy (STM) and scanning electron microscopy (SEM), which showed similar grain sizes on each substrate, suggesting that the dif...

Structure and Phase Transformations in the Titanosilicate, Sitinakite. The Importance of Water

Synchrotron X-ray diffraction and neutron diffraction have been used to investigate the phase changes that the titanosilicate mineral sitinakite undergoes when dehydrated. Refinements of the powder diffraction data of the material before and after heating to 573K indicate a phase change from space group P42/mcm to P42/mbc. Upon exposure to normal atmospheric conditions for an extended period the material transforms back to P42/mcm with a reduced lattice parameter. If the material is heated in a sealed capillary, it is possible to get the two phases coexisting. The coexistence of these two phases in sealed system suggests that it is only the loss of H2O that is driving the reversible phase transformation.

FT-IR and XRD investigations on sintered fluoridated hydroxyapatite composites

Sintered fluoridated hydroxyapatite (FHA) composites were synthesized by calcination at 700 °C for 2 h. The phase changes of the sintered FHA composites have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The effects of the calcination temperature and the presence of calcium fluoride (CaF 2) on the sintered FHA composites were examined. The expanded (300) XRD reflections of sintered FHA composites were significantly different from the uncalcined hydroxyapatite (HA). The XRD reflection peaks of sintered FHA composites gradually shifted to a higher-angle direction when CaF 2 increased. The shift of peaks indicates the a-axis lattice parameter reduction as a result of the calcination process and the substitution of OH by F. The uncalcined composite materials were stable in OH vibrational groups and showed neither OH·F·OH nor OH·F hydrogen bonds. The sintered FHA composites showed FHA phase. With the increase of CaF 2 wt.%, the OH·F·OH and then OH·F hydrogen bonds of sintered FHA composites were forming.

Magnetotransport and magnetoelastic effects in Co-doped La0.7Sr0.3MnO3 nanocrystalline perovskites

La 0.7 Sr 0.3 Mn 1− x Co x O 3 ( x =0, 0.05, 0.1) nanoparticles, prepared by sol–gel method, were studied by means of X-ray diffraction, transmission electron microscopy , resistivity , magnetoresistance , thermal expansion and magnetostriction measurements. Results show that partial substitution of Mn by Co leads to a reduction in lattice parameters , enhancement of resistivity and room temperature magnetoresistance MR, decrease of metal-insulator transition temperature T MI and T C , an increase in thermal expansion coefficient, volume magnetostriction and anisotropic magnetostriction. The latter increases about one order of magnitude with 10% Co substitution. In comparison with Mn ions, the Co ions possess higher anisotropy energy, larger magnetostriction effect, smaller ionic size and spin state transitions with increase in temperature and magnetic field; this suggests that Co substitution leads to double-exchange interaction weakening, resulting in suppression of ferromagnetic long-range order and metallic state and increase of magnetic anisotropy . Furthermore, our samples have a relatively lower T MI and T C , higher resistivity and MR, compared with the reported values for similar compounds with larger particle sizes. This is attributed to the nanometric grain size and spin-polarized tunneling between neighboring grains.

Vacancy effects on Tc in superconducting LaPt1−xSi (0 ⩽ x ⩽ 0.2)

As revealed in the powder X-ray diffraction and crystallographic data, the parent compound LaPtSi, which crystallizes in the LaPtSi-type structure (I41md), admits considerable vacancies up to 20% on the Pt sublattice while still retaining its tetragonal symmetry. The refined lattice parameters show that both the a-axis and the volume of the unit cell v contract clearly, though the c-axis exhibits less percentage change due to the existence of vacancies in the compound. These results are consonant with what one would expect from a chemical pressure effect. Magnetic and heat-capacity measurements demonstrate that the change in Tc with x is similar to the change in the reduced lattice parameters a and v. It is found that the Tc change rate dTc/dx=−9.6±0.6K and dTc/dv=1.5±0.3K/Å3.

Magnetic and Magnetotransport Properties of Diluted Magnetic Semiconductor (Ga,Mn)Sb Crystals

We report the magnetic and magnetotransport properties of Ga1−x Mn x Sb crystals grown with different Mn doping concentrations (x=0.01, 0.02, 0.03 and 0.04) by the horizontal Bridgman technique. A systematic reduction in lattice parameter with increase in Mn concentration is observed through X-ray diffraction studies. The crystals show negative magnetoresistance and anomalous Hall effect below 10 K. Anomalous Hall coefficient is negative and decreases with increasing Mn concentration. Temperature dependence on magnetization measurement shows a magnetic ordering below 10 K which could arise from GaMnSb alloy formation. Also, ferromagnetism is observed till room temperature due to the presence of MnSb clusters. Existence of MnSb clusters is verified through scanning electron microscopy. The carrier concentration increases with Mn doping and this results in decrease of resistivity. The observed magnetic and transport properties indicate the presence of ferromagnetic phase below 10 K in the studied system.

Creep resistance of cast and aged Al–0.1Zr and Al–0.1Zr–0.1Ti (at.%) alloys at 300–400 °C

Cast and aged Al–0.1Zr and Al–0.1Zr–0.1Ti (at.%) alloys, upon compressive creep deformation at 300–400 °C, exhibit threshold stresses attributable to climb-controlled bypass of coherent Al3Zr and Al3(Zr1−xTix) precipitates. Al–0.1Zr–0.1Ti exhibits a smaller threshold stress than Al–0.1Zr, which is attributed principally to a reduced lattice parameter mismatch between the Al3(Zr1−xTix) precipitates and the matrix. The present alloys are less creep resistant than Al–Sc and Al–Sc–Zr/Ti alloys with similar precipitate radii and volume fractions.

Synthesis and investigation of structural and electronic properties of Pr 1−xCa xFeO 3 (0⩽ x⩽0.2) compounds

Single-phase powder compounds of Pr 1− x Ca x FeO 3 ( x = 0 , 0.1 and 0.2) have been synthesized by combustion method using as starting material the corresponding metal nitrates and glycine. The compounds were characterized by X-ray diffraction (XRD), Fe K-edge X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) of core level of Pr 3d, Fe 2p, Ca 2p and O 1s. Rietveld profile refinement technique was employed to analyze the powder diffraction data. All the three compounds showed orthorhombic structure with systematic reduction in lattice parameters. The distortion in FeO 6 octahedra also reduced as x increased. The chemical shift of Fe K-edge showed that the Fe is in 3 + state in PrFeO 3 and its effective charge increased on Ca doping. XPS studies revealed that the ionic state of Pr, Fe and Ca is close to the ionic state of these elements in Pr 2O 3, Fe 2O 3 and CaO, respectively. On substituting Ca for Pr, effective charge on Pr and Fe increased whereas that on O decreased. Change in exchange splitting consistent with the increased effective charge was also observed on Ca doping.

Ion beam characterization of GaAs 1− x− yN xBi y epitaxial layers

Incorporation of Bi in GaAs 1− x N x epitaxial layers represents a significant interest as Bi compensates the lattice parameter reduction caused by the N incorporation while contributing to the reduction of the band gap energy. GaAs 1− x− y N x Bi y epitaxial layers were grown on GaAs wafers by molecular beam epitaxy. The quality of the films as well as the concentration and lattice location of Bi and N were characterized by channeling Rutherford backscattering spectrometry and nuclear reaction analysis using 2 and 3.72 MeV He beams, respectively. The amount of nitrogen in the film was measured by means of the 14N(α, p) 17O endothermic nuclear reaction and elastic recoil detection. The results indicate that high quality epitaxial layers were obtained, with y=1.8% Bi incorporated into the layer. Angular scan along the main axes showed no strain in the film and indicated that most of Bi atoms are located at substitutional sites. Nitrogen lattice incorporation is more difficult to establish because of the presence of Bi in the layer, but we estimate the substitutional fraction to be 71 ± 6%.

Synthesis of nanocrystalline ceria by thermal decomposition and soft-chemistry methods

Nanocrystalline ceria synthesized by different methods have been characterized using TGA-EGA-MS, XRD and HR-TEM. All samples showed stable cubic fluorite structure down to 6 nm particle size. A reduction in lattice parameter with particle size was observed. Effects of synthesis conditions on nano-ceria and grain growth with annealing temperature are discussed.

N+BF 2 and N+C+BF 2 high-dose co-implantation in silicon

Nitrogen and boron BF2, and nitrogen, carbon, and boron BF2 high-dose (6×1016–3×1017 cm-2) co-implantation were performed at energies of about 21–77 keV. Subsequent high-temperature annealing processes (600, 850, and 1200 °C) lead to the formation of three and two surface layers respectively. The outer layer mainly consists of polycrystalline silicon and some amorphous material and Si3N4 inclusions. The inner layer is highly defective crystalline silicon, with some inclusions of Si3N4 too. In the N+B-implanted sample the intermediate layer is amorphous. Co-implantation of boron with nitrogen and with nitrogen and carbon prevents the excessive diffusivity of B and leads to a lattice-parameter reduction of 0.7–1.0%.

Structural and thermal investigations of a high-strength Cu-Zr-Ti-Co bulk metallic glass

Cu 55 Zr 30 Ti 10 Co 5 bulk metallic glass exhibits a high compressive fracture strength of 2.31 GPa and Young's modulus of 130 GPa, values that are higher than those of other Cu- and Zr-based metallic glasses. The addition of Co to the ternary Cu-Zr-Ti alloy stabilizes the supercooled liquid. On heating, the Cu 55 Zr 30 Ti 10 Co 5 metallic glass devitrified and formed an intermediate intermetallic compound prior to reaching equilibrium by diffusion-controlled growth at constant nucleation rate. In the fully annealed state the structure consists of the equilibrium Cu 10 Zr 7 phase with the slightly reduced lattice parameters a = 0.933 nm, b = 0.928 nm and c = 1.254 nm and a small fraction of an unidentified phase.

X-ray reflectivity of ion-beam-deposited Ag/Al multilayers

Multilayer films with modulation wavelengths between 1.35 and 21.3 nm, and a total thickness of less than 1 μm were deposited using dual-ion-beam sputtering technique. X-ray reflectivity of the Ag/Al multilayers with 2, 4, 8 and 14, deposited on silicon substrates was measured using high-resolution diffractometer. From the analysis of the data, it has been shown that both the period and the refractive index can be obtained simultaneously from these measurements. In this formulation, Bragg equation corrected for the refractive index of the multilayer film is used. For short modulation wavelengths, less than 3.5 nm, an additional layer of intermetallic Ag 2Al was formed as determined by the X-ray diffraction peaks. The average lattice parameter was reduced for shorter modulation wavelengths and approached the bulk value for wavelengths above 5.0 nm. The reduced lattice parameter for shorter wavelengths is consistent with the recent results on the nanometer-sized particles of other materials and could be explained arising due to surface energy consideration.

Evidence of Be3P2 formation during growth of Be-doped phosphorus-based semiconductor compounds

In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (>1018 cm−3) and temperatures higher than 500 °C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general.

Carbon self-organization in the ternary Si1−x−yGexCy alloy

This article demonstrates for the first time the possible self-ordering of carbon in Si1−x−yGexCy thin films pseudomorphically grown on silicon. Germanium and carbon atomic distributions have been studied for a C-rich Si0.9−yGe0.1Cy heterostructure using high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction, Raman spectrometry, and secondary ion mass spectrometry (SIMS). HRTEM images show the spontaneous formation of carbon-rich tilted sublattices and local germanium fluctuations, despite constant growth parameters. X-ray diffraction confirms this thin sublayers formation. A complementary insight into local ordering effects around C is obtained by Raman spectroscopy. A new model for perpendicular lattice parameter reduction is proposed. It involves C atoms mostly in third-nearest-neighbor positions and the local formation of a distorted CSi3 graphitic arrangement. In these C-rich sublayers, the perpendicular lattice mismatch to silicon is as low as −0.014. This aperiodic structure remains highly distorted and a statistical description of these strain fluctuations is detailed. The atomistic configuration of these δ layers indicates the likely contribution of surface steps during the growth, while SIMS measurements hint at the probable involvement of carbon interstitials to explain this ordering. For technological applications, this self-organization of carbon is promising for the ultrashallow junction challenge. These carbon-rich embedded layers can be considered as quantum wells, etch stops or very thin barriers against transient enhanced diffusion.

The effect of substrate orientation on the properties of low temperature molecular beam epitaxial GaAs

GaAs and related materials, grown by molecular beam epitaxy at 200–300 °C under normal, group V-rich conditions are highly nonstoichiometric, with excess group V concentrations of up to 1021 cm−3, and the material properties are defect controlled. Here we report on comparative studies of low temperature growth of GaAs on (100) substrates and on (111)A, (111)B, (311)A, and (311)B surfaces. We show that material grown on both the (111) faces, under As-rich conditions, becomes polycrystalline almost immediately after commencement of growth. We attribute this to faceting of the surface creating regions of excessive As incorporation and either directly nucleating misorientated growth or producing areas of extreme localized strain resulting in the breakdown of crystallinity. Layers grown on (311)A and (311)B surfaces are of good crystalline quality but are highly nonstoichiometric in both cases, contrary to the anticipation that the (311)A surface, having fewer available forward Ga bonds than the (100) or (311)B surfaces might have a lower affinity for As incorporation. We also describe the reduction of excess As incorporation into layers grown on both (311) surfaces in the presence of Si or Be doping concentrations of 1×1019 cm−3 or greater, as we previously reported for layers grown on (100) substrates. This is evidenced by the reduced lattice parameter and lower absorption in the near-band-edge infrared region due to As antisite defects, compared to undoped material. Also, little or no hopping conduction is seen in Be doped layers although they are totally compensated. A proportion of donors are active in the Si doped layers and the conduction mechanism seems to be normal band conductivity. Electrical activation of the Si donors and Be acceptors can be increased, however, only after high temperature annealing.