Lattice Constant Measurements Research Articles

Optical reflectivity studies of radiation-induced trace disorder in silicon

For the first time, the effect of randomly distributed volume defects, induced by fast neutrons, on the reflectivity spectrum of crystalline Si has been studied. Reflectivity ( R) measurements were performed at 300 K in the range 3.7–11 eV. The influence of surface preparation on the quality of an R spectrum was checked. Proper surface treatment allowed additional features to be revealed of the reflectivity spectrum. It has been found that neutron irradiation tends to reduce the reflectivity of Si similarly as ion implantation does. Analysis of the reflectivity drop (Δ R), considering the defect structure of neutron-irradiated Si, allowed a correlation between Δ R and the concentration of the main defect species to be found. Precise measurements of the Si lattice constant have shown no changes of the single-crystal structure after neutron irradiation. The paper proves a very high sensitivity of optical reflection spectroscopy to the trace perturbation of the single crystalline lattice of silicon.

Synthesis of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Using a Carbon Dioxide Laser

The synthesis and the structure of silicon carbide‐silicon nitride (SiC─Si3N4) composite ultrafine particles have been studied. SiC─Si3N4 composite ultrafine particles were prepared by irradiating a SiH4, C2H4, and NH3 gas mixture with a CO2 laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β‐SiC structure. As the nitrogen con‐ tent increased, SiC decreased and amorphous phase, Si3N4, Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles.

A 109high-pressure cell for X-ray and optical measurements

The construction of a new high-pressure cell is presented. It is a piston-cylinder type of apparatus. The entrance and exit of X-rays or light are possible through two parallel diamond-plate windows placed on V-shaped slits covering almost the whole range of reflection angles. This makes the cell particularly suitable for X-ray diffraction examinations of monocrystals. The potential accuracy of absolute-bulk-modulus determination by lattice-constant measurements using the Bond method [Bond (1960). Acta Cryst. 13, 814–816] at pressures of 108–109 Pa can be estimated at 1–2%. The cell enables the simultaneous examination of two samples, which makes possible the comparison of their compressibilities with an accuracy of 0.01–0.1%. As examples, the results of compressibility measurements on GaAs and GaN are given.

X-ray examination of GaN single crystals grown at high hydrostatic pressure

Gallium nitride single crystals grown at temperatures 1200–1600°C and pressures 12–20 kbar were examined with X-ray diffractometry. The narrow (about 20 arc sec) peaks of the (00.4) reflection obtained with a non-dispersive double crystal arrangement proved the high crystallographic perfection of the plate-like crystals. This enabled the measurement of lattice constants using the highly accurate Bond method. The analysis of a set of symmetrical and asymmetrical reflections gave the following values of GaN lattice constants: a = 3.1879 ± 0.0003 A ̊ and c = 5.1856 ± 0.0001 A ̊ .

Low-temperature X-ray powder diffraction of Bi2Sr2CaCu2Oxsuperconductor

Abstract A low-temperature X-ray powder diffractometer has been developed and applied to the measurement of lattice constants of Bi2Sr2CaCu2O x superconductor at 80 K, only 3 K higher than the critical temperature. The relationship between the lattice constants and electrical resistivity was studied. The Bi2Sr2CaCu2O x sample was prepared by solid-state reaction and sintered by a hot-press system at 750°C. Lattice constants of the Bi2Sr2CaCu2C x were measured at 293 to 80 K. The electrical resistivity of the sample, measured by the standard four-probe method, reached 0 Ω cm at 77 K. The resistivity decreased rapidly along with rapid shrinkage of the c-axial length.

The growth and characterization of Si1−yCy alloys on Si(001) substrate

We have prepared Si1−yCy alloy layers on Si (001) substrates using solid-source molecular-beam epitaxy. The lattice mismatch between diamond and Si is about 50%. Thus, a Si1−yCy (y=0.02) alloy has a mismatch of about 1% with respect to Si assuming Vegard’s law. Transmission electron microscopy (TEM) shows the layers to be pseudomorphic. Growth temperatures between Tg=500–550 °C are suitable for Si1−yCy layers with y≤0.05 for a growth rate of about 0.2 nm/s. Raman spectra show a distinct phonon mode at 600 cm−1, which is characteristic of substitutional carbon in Si. The Raman spectra show no evidence of silicon carbide precipitates, nor are precipitates observed in the cross-sectional TEM micrographs. This is consistent with the lattice constant measurements by x-ray diffraction. Amorphous growth occurs for lower substrate temperatures or significantly higher carbon concentration. That means, with increasing y in the Si1−yCy alloy layer the substrate temperature must be increased moderately. We have also studied the thermal stability of Si1−yCy strained-layer superlattices and find that the layers are stable to about 800 °C (for y=0.015). The ability to grow high-quality Si1−yCy alloy layers and Si1−yCy/Si superlattices adds a new dimension to Si-based band-gap engineering with the possibility for integration of a potential wide band-gap semiconductor into Si technology.

Predominant defects in semiconductor isovalent solid solutions: Pb1 –y(SexTe1 –x)y, Pb1 –y(SxTe1 –x)yand Pb1 –y(SxSe1 –x)y

Isovalent ternary solid solutions of AIVBVI materials such as Pb1 –y(SxSe1 –x)y, Pb1 –y(SxTe1 –x)y, and Pb1 –y(SexTe1 –x)y can been used as lattice-matched heterostructures for IR lasers and detectors. The solid/vapour equilibrium has been studied by the method of rapid quenching of crystals of solid solutions prepared by three-zone furnace annealing at fixed T, PPb and PPbX. Hall-coefficient and lattice-constant measurements on quenched samples were analysed as functions of T and PPb. The curves of n, p as functions of T and PPb were used to determine the degree of ionization of defects and to calculate the constants of Frenkel disordering in the form: K=K0 exp(–ΔH/kBT).

X-ray Diffraction Analysis of Graphite Materials

The procedure for the measurement of lattice constants and crystallite sizes of artificial graphite materials was proposed by the 117th Committee (Carbon Materials) in Japan Society for the Promotion of Science and called “Gakushin method”. It has been used in many companies in Japan since 1963. As a part of activity of New Carbon Forum, its usage in companies was explored by sending questionnaires. The several factors affecting on X-ray diffraction profiles, selection of slit system, mixing ratio of inner standard silicon, compaction of sample powder, etc., were studied.

Magnetic, magneto-optic, and transport properties of Tb-doped EuS films

Films of EuS have been doped with up to 34-at. % Tb by coevaporation. From lattice constant measurements we conclude that the films are defect rocksalt structure solid solutions with the general formula Eu1−xTbxS1−y⧠y, where ⧠ represents a vacancy. The magnetic properties change drastically between undoped films and the Tb substituted samples. The Curie point increases from 20 to about 135 K and the coercivity increases from 60 Oe to about 4 kOe in the x=0.34 sample. Our measurements indicate an increase in RKKY exchange because of the higher carrier concentration caused by Tb doping. The increased carrier density causes a decrease in resistivity of at least two orders of magnitude to about 10−3 Ω cm, the same order of magnitude as reported for bulk solid solutions of EuS-GdS. The peaks in the magneto-optic Kerr spectrum of EuS at about 2 eV are decreased in amplitude, broadened and shifted in energy with Tb doping.

Isotopic dependence of the lattice constant of diamond.

We report measurements of lattice constants of single-crystal synthetic diamonds that cover the range of isotopic compositions from almost-pure $^{12}\mathrm{C}$ to almost-pure $^{13}\mathrm{C}$. These provide a demonstration of an effect of isotopic composition on the lattice constant of this material. The results are consistent with a linear dependence ${\mathit{a}}_{0}$(C,25 \ifmmode^\circ\else\textdegree\fi{}C,x)=3.567 15-0.000 53x \AA{}, where x is the atom fraction of $^{13}\mathrm{C}$. This corresponds to a fractional change between the end compositions of \ensuremath{\Delta}${\mathit{a}}_{0}$/${\mathit{a}}_{0}$=-1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, which is less than the smallest value in a range of theoretical estimates that have been published previously. The synthetic diamonds yielded (400) Bragg peaks with widths in the range 12--17 arc sec that are not perceptibly dependent on the isotopic composition.

Magnetic and structural properties of Fe in single crystals of YBa2Cu3-xFexO7- delta.

Magnetization and lattice-constant measurements were done on four single crystals of YBa{sub 2}Cu{sub 3{minus}{ital x}}Fe{sub {ital x}}O{sub 7{minus}{delta}} with Fe concentrations of {ital x}=0.06, 0.09, 0.15, and 0.24 to determine the structural and normal-state properties. Measurements of magnetization as a function of temperature were done in a temperature range between 90 and 300 K and analyzed using a Curie-Weiss law with a temperature-independent background. The effective magnetic moment obtained corresponds to a low spin state of Fe{sup 3+} with a magnitude of 2.18{mu}{sub {ital B}}. Magnetic anisotropy between the {ital ab} plane and the {ital c} direction is only present for the concentration of {ital x}=0.06 and is attributed to the various oxygen environments surrounding the iron. For concentrations larger than {ital x}=0.06, the moment on Fe is isotropic and Curie-Weiss fits predict uniform antiferromagnetic ordering. Structural measurements exhibit an orthorhombic-tetragonal transition at an Fe concentration of {ital x}=0.15, similar to that observed in the polycrystalline material.

Synthesis, structure, and properties of LaSrCuGaO5

AbstractThe new brownmillerite‐related compound, LaSrCuGaO5, has been synthesized and characterized. It crystallizes in the orthorhombic non‐centrosymmetric space group Ima2. The unit cell dimensions are a = 16.383(1) Å, b = 5.5293(7) Å, c = 5.3275(6) Å. The structure is related to perovskite but contains ordered oxygen vacancies within the two‐dimensional gallium oxygen layers resulting in tetrahedral coordination of the gallium cations. Other important structural features include buckled copper‐oxygen planes, and disorder of the lanthanum and strontium cations over the A‐site. Accurate lattice constant measurements reveal an a‐axis expansion of 0.17 Å when doped with strontium La1–xSr1+xCuGaO5 (xmax = 0.13). Magnetic susceptibility measurements demonstrate that the compound remains paramagnetic to 4 K.

The effect of oxygen on the thermal stability of Si1−xGex strained layers

The thermal stability of Si1−xGex strained layers containing 2×1020 oxygen atoms/cm3 is compared with that of similar layers (same Ge fraction and film thickness) containing more than two orders of magnitude less oxygen. For the layers with high oxygen levels, no misfit dislocations were found in films as thick as two times the theoretical equilibrium critical thickness, after annealing at 850 °C for 4 min. In contrast, dislocations were found in the layers with low oxygen levels at thicknesses very near the equilibrium critical thickness after the same anneal. X-ray measurements of lattice constants in high and low oxygen films of similar Ge content indicate that oxygen does not substantially change the amount of strain in the layers. Oxygen appears to impede the kinetics of dislocation formation.

Synthesis, crystal structure, and properties of metallic PrNiO 3: Comparison with metallic NdNiO 3 and semiconducting SmNiO 3

The compound PrNiO 3 has been prepared for the first time. Using only moderate oxygen pressure, PrNiO 3, NdNiO 3, and SmNiO 3 were made and found to crystallize in the GdFeO 3—type orthorhombically distored perovskite structure. Structural refinements for all three compounds reveal NiO 6 octahedra with an average NiO distance of 1.94–1.95 Å, about the same as in the more distorted HoNiO 3. The electrical conductivity of PrNiO 3 is metallic at room temperature, but undergoes a transition at 130 K to an insulating state. Examination of the conductivities of the corresponding Sm, Nd, and La compounds reveals a monotonic pattern of behavior: as the rare earth radius is increased, the compounds become more conducting because the metal-insulator transition temperature decreases from 400 K(Sm) to 200 K(Nd) to 130 K(Pr) to none for La. From DSC and lattice constant measurements, this transition is shown to be first order, with a ∼0.2% contraction upon heating into the metallic state. Low temperature neutron measurements in the insulating phase reveal new diffraction peaks, probably related to magnetic ordering of Ni and/or RE moments.

Preparation and lattice constant measurement of (Ca + Cd + Pb) hydroxylapatites

Preparation and lattice constant measurement of (Ca + Cd + Pb) hydroxylapatites

The hP1-type phases in alloys of cadmium, mercury, and indium with tin

The hP1-type phases in alloys of Cd, Hg, and In with Sn are stable in the valence electron concentration interval 3.80–3.95. Following a rule of Raynor, the axial ratioc/a decreases with increasing valence electron concentration,Nb/at. Using lattice constant measurements the rule is confirmed, and by using density measurements the absence of constitutional vacancies is verified. Thec/a→Nb/at relation of the hP1 phases is similar toc/a→Nb/at of InSnm (0<m<0.1) and In3Sn. A bonding-type proposal, explaining the stability of these structures and the dependence of their axial ratio on valence electron concentration, is derived.

Pressure-dependent phonon properties of III-V compound semiconductors.

Using a phenomenological lattice-dynamical theory in the quasiharmonic approximation, we present a comprehensive study to understand the effects of pressure on the vibrational properties of Ga-In pnictides that exhibit a sphalerite crystal structure. The existing pressure-induced Raman scattering data for phonon frequencies, the ultrasonic measurements of elastic and lattice constants, are used as constraints to stringently test the reliability of our rigid-ion model. The effects of high pressure on phonon dispersion curves are shown to lead to a softening in the transverse acoustic modes. At low temperatures this provides a possible driving mechanism for the decrease in the Debye temperature and the occurrence of a negative Gr\uneisen constant and thermal-expansion coefficient in semiconductors. With a few exceptions (InP, GaAs, and GaSb), our calculated values for several elemental and compound semiconductors have qualitatively satisfied the empirical linear relationship between the Gr\uneisen parameter ${\ensuremath{\gamma}}_{\mathrm{T}\mathrm{A}(\mathit{X})}$ and the transition pressure ${\mathit{P}}_{\mathit{t}}$. Numerical results for the lattice dynamics, one-phonon and two-phonon density of states, Debye temperature, Gr\uneisen constant, and linear thermal-expansion coefficient are all shown to be in reasonably good agreement with the existing experimental data.

ChemInform Abstract: Solid Solutions of Calcium‐Copper‐Zinc Hydroxylapatites: Preparation and IR and Lattice Constant Measurements.

AbstractHomogeneous solid solutions of hydroxylapatites Ca10‐(m+n)CumZnn(PO4)6(OH)2 with a fixed value of m = 1 are synthesized over the entire composition range using a new coprecipitation technique starting from aqueous NH4H2PO4 solution and solutions containing Ca‐, Cu‐, or Zn‐nitrate.

Substitution of 3d metals for Cu in Bi2(Sr0.6Ca0.4)3Cu2Oy.

The effect of the substitution of 3d metals (Fe, Co, Ni, and Zn) for Cu in a high-temperature superconductor ${\mathrm{Bi}}_{2}$(Sr,Ca${)}_{3}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{\mathit{y}}$ was investigated by measuring lattice constants, dc resistivity, Hall effect, and magnetic susceptibilities in normal and superconducting phases. For all kinds of impurities, within the composition range where the single-phase samples are synthesized, the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ was found to decrease with increasing impurity concentration. Even nonmagnetic Zn was found to decrease ${\mathit{T}}_{\mathit{c}}$, as well as, magnetic Fe, Co, and Ni, without changing the hole concentration. These behaviors cannot be explained by the Abrikosov-Gorkov theory for conventional BCS superconductors. Possible explanations are discussed.

Dispersion of ZrO2 grains in ZrO2-Al2O3 composite powders prepared from Zr-Al organometallic compound

ZrO2-Al2O3 composite powders have been prepared from a Zr-Al organometallic compound by thermal decomposition. X-ray diffraction patterns have indicated that the powders are amorphous below 800° C but tetragonal ZrO2 appears above 900° C and subsequently α-Al2O3and monoclinic ZrO2 appear above 1200°C. Transmission electron microscope analysis has shown that fine grains (5 to 20 nm in diameter) of ZrO2 are homogeneously dispersed in the ZrO2-Al2O3 composite particle and they grow in size with increase in the heating temperature. The measured lattice constants of α-Al2O3 phase have revealed that Zr atoms are practically insoluble (<0.2at%) in the α-Al2O3 phase.