Room Temperature Lattice Constants Research Articles

Thermal Expansion of Oxyarsenides (LaO)TAs; T = Transition Metal

We have investigated the precise crystal structure and their temperature dependences of oxyarsenides (LaO)TAs; T = Mn, Fe, Co, as the Fe based superconductor’s parent material family using high energy synchrotron radiation x-ray powder diffraction. Lattice constants a and c decrease with decreasing temperature. Focusing the ratios of the changes normalized by room temperature lattice constants, we have found anisotropic shrinks for the superconductor’s parent material of (LaO)FeAs and the ferromagnetic metal (LaO)CoAs. The shrinkage of the lattice constant c along the stacking direction will be discussed by the temperature dependence of the divided three components of the LaO layer, TAs layer, and the interlayer distance.

Heat Capacity and Thermal Expansion of Uranium-Gadolinium Mixed Oxides

Uranium-gadolinium mixed oxides of four different compositions, (U1-y Gdy) O2±x (y = 0.1, 0.2, 0.5, and 0.8), were synthesized. Single-phase fluorite structure was observed for the compositions (U1-y Gdy) O2±x (y = 0.1, 0.2, and 0.5). The room temperature lattice constants measured for (U0.9 Gd0.1) O2.02, (U0.8 Gd0.2) O2.00, and (U0.5 Gd0.5) O1.98 are 0.5463, 0.5454, and 0.5433 nm, respectively. Heat capacity measurements in the temperature range 298 – 800 K were carried out using a differential scanning calorimetry. Considerable anomalous increases in the heat capacity values were observed for compositions (U1-y Gdy) O2±x with y = 0.1, 0.2, and 0.5. The heat capacity values of (U0.9 Gd0.1) O2.02, (U0.8 Gd0.2) O2.00, and (U0.5 Gd0.5) O1.98 at 298 K are 63.5, 61.1, and 65.7, respectively. Thermal expansion characteristics of (U0.9 Gd0.1) O2.02, (U0.8 Gd0.2) O2.00, and (U0.5 Gd0.5) O1.98 were studied using a high temperature X-ray diffraction in the temperature range 298 – 1973 K.

Synthesis, structure and properties of Li 2Rh 3B 2

Li 2Rh 3B 2 has been synthesized at 1000 °C from a stoichiometric mix of rhodium and boron and an excess of lithium. Li 2Rh 3B 2 crystallizes in the orthorhombic space group Pbam (no. 55, Z=2) with room temperature lattice constants a=5.7712(1) Å, b=9.4377(2) Å, c=2.8301(1) Å and cell volume 154.149(6) Å 3. The structure was solved from single crystal X-ray diffraction yielding the final R indices (all data) R1=2.8% and w R2=4.7%. The structure is a distortion of the CeCo 3B 2 structure type, containing a network of Rh 6B trigonal prisms and short Li–Li contacts of 2.28(2) Å. Li 2Rh 3B 2 is a diamagnetic metal with a room temperature resistivity of 19 μΩ cm, as determined by magnetic susceptibility and single crystal transport measurements. The measured diamagnetism and electronic structure calculations show that Li 2Rh 3B 2 contains rhodium in a d 10 configuration.

Lattice constants and anisotropic microstrain at low temperature in 242Pu–Ga alloys

We attempted to characterize by neutron powder diffraction the monoclinic α′ phase that is known to form at low temperatures in dilute Pu–Ga alloys. This attempt was unsuccessful, as we did not detect any transformation to the α′ phase, but instead observed a line-broadening effect in the fcc δ phase. This effect is large enough to be visible in the raw diffraction data and is highly anisotropic in crystal space. The onset temperature of the line broadening (150 K) coincides with previous observations of the δ–α′ transformation. Bulk α′ was not observed. We believe that the development of α′ nuclei creates a spatially inhomogeneous stress distribution in the δ matrix, which in turn exhibits an anisotropic response, governed by its elastic anisotropy. We have analysed this observation of anisotropic microstrains in terms of the fictive microstresses required to produce them by elastic deformation. During the course of this work, we found a pseudo-isotope effect in the room temperature lattice constants of Pu–Ga alloys. The alloys made from nominal 242Pu isotope show systematically higher lattice constants than the corresponding 239Pu alloys, and the size of the effect is proportional to the Ga concentration. We believe that this effect is associated with the higher levels of radiation damage from isotopic impurities in the 242Pu alloys.

Growth and physical properties of epitaxial HfN layers on MgO(001)

Stoichiometric HfN layers, with N/Hf=1.0±0.03, were grown on MgO(001) substrates at 650 °C by ultrahigh-vacuum magnetically unbalanced magnetron sputter deposition in mixed N2/Ar discharges at 20 mTorr (2.67 Pa). High-resolution x-ray diffraction ω-2θ and azimuthal φ scans combined with cross-sectional transmission electron microscopy establish that HfN grows epitaxially with a cube-on-cube orientational relationship to the substrate: (001)HfN∥(001)MgO and [100]HfN∥[100]MgO. The layers are fully relaxed at the growth temperature and have a room-temperature bulk lattice constant of 0.4524 nm. Electronic transport measurements show that HfN is metallic with a room-temperature resistivity of 14.2 μΩ cm, an n-type carrier concentration of 4.8×1021 cm−3, and an electron mobility of 86 cm2 V−1 s−1. The resistivity ρ remains constant at 3.5 μΩ cm, limited by defect scattering, between 10 and 50 K, while at higher temperatures ρ increases linearly and is limited primarily by phonon scattering. HfN(001) is also superconducting with a critical temperature of 9.18 K. The hardness and elastic modulus of HfN(001) were determined from nanoindentation measurements to be 25.2±0.7 and 450±9 GPa, respectively.

Neutron Diffraction Study on Intermetallic Er<sub>5</sub>Mg<sub>24</sub> and Tm<sub>5</sub>Mg<sub>24</sub>

Neutron powder diffraction on the binary intermetallics Er5Mg24 and Tm5Mg24 confirms their isostructural and pure crystallization in the Ti5Re24-type structure (space group I 4 3m, Z = 2)with rare earths located in 2a(0,0,0) and 8c(x,x,x) and Mg in two different 24g(x,y,x) sites. Room temperature lattice constants are 11.263(2) Å and 11.215(1) Å for the Er and Tm compound, respectively. Atomic positions have been refined. Both compounds order ferromagnetically below Curie temperatures of 17.5(5) K and 7.5(5) K for Er5Mg24 and Tm5Mg24, respectively. The magnitudes of the Er moments at 4.2 K are 7.5(2) µB and 4.4(2)µB on the 2a and the 8c sites, respectively. The Tm moments which have been refined from 2 K measurements amount to 3.0(3)µB and 2.8(2) µB, respectively. The temperature dependencies of the magnetic Bragg intensities reveal distinct deviations from Brillouin curves for J = 15/2 (Er) and J = 6 (Tm) systems and indicate a complex magnetic exchange.

Hardness behaviour in B2 pseudo-binary systems

Room-temperature hardness data and lattice constants were assembled for a number of Ru and Ir-based ternary systems exhibiting continuous B2 (CsCl) phase fields between the binary compounds. Near-linear relationships were found to exist in the hardness profiles and lattice constants of the RuAlRuTi, RuAlCoAl, RuAlIrAl, IrAlNiAl and RuAlRu 2NbAl (L2 1) pseudo-binary series, suggesting a strong correlation of hardness with just one parameter. Pronounced solution hardening is reported for the RuAlNiAl, RuTiNiTi and RuZrPdZr series. In these cases, no clear correlations with the lattice parameters could be found, indicative of constitutional effects such as defects and ternary ordering. Volume size factors were examined as a basis for predicting lattice constants in these systems. Where such data exist, it was generally found that quantitative size factors yield errors commensurate with the precision of the available data.

The Néel temperature of Mn100−xRhx alloys in ordered and disordered states

The concentration dependence of the room-temperature lattice constant and the Néel temperature of Mn100−xRhx (15⩽x⩽30) disordered and ordered alloys was investigated in order to clarify the difference in the antiferromagnetic properties. The room-temperature lattice constant increases with increasing x and the difference between the disordered and ordered alloys was hardly observed. The Néel temperature increases with increasing x in both the disordered and ordered states. This behavior is not explained by the variation of the strength of the exchange interaction as a function of the Mn–Mn distance but by the number of 3d electrons in the Mn site. The Néel temperature in the ordered state is 130–160 K higher than that in the disordered state, indicating that the exchange interaction is enhanced by ordering.

Transport properties of L1-xSrxMnO3 (L=Pr, Nd; 1/4

We report on the temperature dependence of the zero-field resistivity (\ensuremath{\rho}), absolute thermopower (S) and the room temperature lattice constants of the title materials. The results indicate that at high temperatures, above the transition to the ferromagnetic (FM) state electronic transport is carried out in narrow bands. An attempt to account for the measured values of S was put forward. Evidence for the presence of a gap in the density of states of the compounds with x\ensuremath{\sim}1/4, possibly due to Coulomb repulsion, was found in S(T) at temperatures far above ${\mathit{T}}_{\mathit{c}}$. The positive sign of S found in the FM state of most of the compounds studied is consistent with transport in a one-electron band with polarized states. The temperature dependence of the resistivity in the FM state is consistent with a transition probability which depends exponentially on the transfer integral. \textcopyright{} 1996 The American Physical Society.

Transport properties of Nd1−x Sr x MnO3 (1/4≤x≤1/2)

We report on the temperature dependence of the thermopower and of the zero-field resistivity for the title compounds, on their room temperature lattice constants and on magnetoresistance measured forx=1/4.

The Bond N-Cl. Crystal Structures and 35Cl NQR of N-Chloro-N-Phenyl-2-chloroacetamide, N-Chloro-N-phenyl-2,2-dichloroacetamide, N-Chloro-N-phenyl-2,2,2-trichloroacetamide, and N-Phenyl-2,2,2-trichloroacetamide

Abstract The crystal structures of C6H5NClCOCH2Cl (1), C6H5NClCOCHCl2 (2), C6H5NClCOCCl3 (3), and C6H5NHCOCCl3 (4) have been determined at room temperature (lattice constants, d in pm).(1): P21 /c, Z = 4, a = 738, b = 645, c = 1891, β = 90.41°, d (N -C l) = 171, d (C = O ) = 121; (2): P21 /c, Z = 4, a = 820, b = 1495, c = 905, β = 114.78°, d (N -Cl) = 171, d (C = O ) = 120; (3): P 21/c, Z = 4, a = 819, b = 1853, c = 718, β = 103.64°, d (N -Cl) = 172, d (C = O ) = 120; (4): P21/c, Z = 4, a = 551, b = 1704, c = 1035, β = 93.08°, d (C = O) = 121. For (2), (3), and (4) the 35Cl NQR frequencies have been determined in the range 77 ≤ T /K ≤ 300. At 77 K (γ in MHz): (2): γ(w,1) = 37.600, γ(w,2) = 38.188, γ(N) = 51.858; (3): γ(w,1) = 39.944, γ(w,2) = 40.512, γ(w,3) = 40.739, γ(N) = 52.791; (4): γ(w,1) = 39.428, γ(w,2) = 39.452, γ(w,3) = 39.986. For the compound C6H5NHCOCHCl2 (5) the 35Cl NQ R measured at 77 K is: γ(w,1) = 37.195 MHz, γ(w,2) = 37.596 MHz. The relation, γ(35Cl) = d (N -Cl) is discussed.

First Principle Self-Consistent Pseudopotential Calculation on the Electronic Structure of (InAs)1(GaAs)1 Superlattice

The band structure of the (InAs)1(GaAs)1 strained superlattice is calculated by the self-consistent pseudopotential method. The results show that the (InAs)1(GaAs)1 is a direct-gap superlattice. With the local density approximation, the band gap calculated with the room-temperature lattice constants is 0.43eV, and the corrected value is 0.91eV, in agreement with experimental results. Because of the lattice mismatch between InAs and GaAs layers, the three-fold degenerate energy level at the top of valence band splits into two levels with a spacing of 0.29eV. The splitting of energy level is also estimated and explained using the effective-mass theory.

Magnetic and thermodynamic properties of nonsuperconducting (Y,Pr)Ba2Cu3O6

The concentration dependence of the room-temperature lattice constants and the concentration and temperature dependence of the specific heat C(T) and the magnetic susceptibility have been measured on the tetragonal, nonsuperconducting phase of Y1−xPrxBa2Cu3O6. The effective paramagnetic moment μeff is independent of x and has an average value of 2.7±0.2 μB. For PrBa2Cu3O6, the Néel temperature TN for Pr moment ordering is 10.5 K as compared to TN=17 K for the orthorhombic PrBa2Cu3O7 phase. The TN is depressed rapidly with Y doping in the oxygen-depleted compound and goes to zero at x≊0.4–0.5. At low temperatures and x≤0.5, C(T)/T vs T2 is nonlinear and shows a rapid decrease of C(T)/T indicative of strong magnetic correlations.

On the lattice parameter of some sesquioxides with the fluorite structure

Lattice constants for hypothetical room-temperature fluorite forms of Bi 2O 3 and rare-earth oxides are determined by application of Vegard's rule to fluorite solid solutions. Analysis shows that there are at least two different fluorite structures for sesquioxides, thereby explaining anomalous thermal expansivity data in the literature. A general equation for the prediction of room-temperature lattice constants for fluorite sesquioxide solid solutions is presented.

Epitaxial growth of γ-Fe on Ni{001}

The epitaxial growth of Fe on Ni{001} is studied by means of low-energy electron diffraction (LEED) and Auger-electron spectroscopy (AES). Films thinner than about 4 atomic layers produce 1 × 1 LEED patterns and are found to be epitaxial, but with markedly expanded interlayer spacings. Films thicker than about 6 layers (up to 25 layers) produce 1 × 1 patterns with weak satellite beams that are attributed to the presence of bcc Fe{110} islands. A LEED analysis of the 1 × 1 component of a 10-layer Fe film reveals a body-centered tetragonal structure with bulk lattice parameters a = 2.489 Å (dictated by the Ni{001} substrate) and c = 3.88 Å (i.e., interlayer spacing d bulk = 1.94 Å, expanded 10% over the Ni spacing 1.76 Å). The first interlayer spacing d 12 is expanded 5% with respect to the bulk. Strain analysis estimates that the equilibrium room-temperature lattice constant of the Fe phase grown in these experiments is 3.65 ± 0.04 Å, consistent with the results reported elsewhere for Fe films grown on Cu{001}. This information, combined with the results of total-energy band-structure calculations published elsewhere, shows that the γ-Fe phase grown in the present experiments is expanded with respect to the non-magnetic state, and has a strain that is slightly smaller in the ferromagnetic than in the antiferromagnetic state.

Magnetic to nonmagnetic transition in a highly hybridized f-electron system: U(Ga1−xGex)3

UGa3 is an antiferromagnetic system with a Néel temperature TN =67 K and UGe3 is a weakly paramagnetic system with a nearly temperature-independent magnetic susceptibility and a slightly enhanced low-temperature electronic specific heat coefficient of 20 mJ/mole K2. The room-temperature lattice constant and the temperature dependence of the magnetic susceptibility, electrical resistivity, and low-temperature specific heat have been measured for the pseudobinary alloy system, U(Ga1−xGex)3. TN is rapidly depressed with increasing x and appears to go to zero at x≂0.18. The magnetic susceptibility remains nearly temperature independent across the series and neither the magnetic susceptibility nor low-temperature specific heat display any significant enhancement in the paramagnetic regime.

Precise lattice constants and thermal expansion of K2Pt(CN)4Br0.3.3H2O

Room-temperature lattice constants and thermal expansion of K2Pt(CN)4Br0.3.3H2O determined from single-crystal X-ray diffraction are reported.

Bandgap and lattice constant of GaInAsP as a function of alloy composition

Published data for the composition dependence of the room-temperature bandgap (Eg) and lattice constant (ao) in the pseudobinary GayIn1-yAs, GayIn1-yP, GaAsxPl-x, and InAsxPl-x systems have been used to derive the following equations for the quaternary GayInl-yAsx Pl-x, alloys: $$\begin{gathered} a_o ({\AA}) = 5.87 + 0.18x - 0.42y + 0.02xy \hfill \\ E_g (eV) = 1.35 - x + 1.4y - 0.33xy - (0.758 - 0.28x)y(1 - y) \hfill \\ - (0.101 + 0.109y) x(1 - x). \hfill \\ \end{gathered} $$

Thermal expansion of lattice parameters of some rare earth gallium garnets and magnetic bubble domain materials

The rare earth gallium garnets Dy <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , Gd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , and Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> used as substrate materials and the magnetic film materials EuEr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5-x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0 \leq x \leq 5</tex> ) and Eu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Er <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0 \leq x \leq 3</tex> ) have been prepared and their lattice parameters measured between room temperature and 1200°C. In the series R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , the room temperature lattice constant decreases linearly in the order Nd>Sm>Gd>Dy. The curve <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa/a_{0}</tex> (a <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> = lattice constant at 25°C, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa</tex> = lattice constant - a <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> versus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> shows a very slight concavity over the whole temperature interval with higher values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa/a_{0}</tex> in the same order as the room temperature lattice constants. The lattice constants follow Vegard's law with the substitution of europium for erbium in the series Eu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Er <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> and decrease with decreasing europium content. The curves of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa/a_{0}</tex> have the same shape as the rare earth gallium garnets, but with higher values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa/a_{0}</tex> in the opposite order to the room temperature lattice constants. Substitution of gallium for iron in the series EuEr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5-x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> caused positive deviation from Vegard's law and a decrease in the room temperature lattice constants. The values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Deltaa/a_{0}</tex> increase with increasing iron content. The implications of these observations on the properties of magnetic films for bubble domain applications are discussed.

The dioxide of 248Cm

The dioxide of curium has been prepared on the microgram scale with long-lived 248Cm (t12=3·5×105 yr) and found to exhibit the face-centered cubic, fluorite-type structure with an average, room-temperature lattice constant of 5·359 ± 0·002 Å. This value is significantly lower than all previously reported values, which is consistent with our contention that the earlier samples suffered from radiation-induced expansion. The curium(IV) ionic radius is calculated to be 0·880 Å. Plots of the actinide dioxide lattice parameter and tetravalent ionic radius vs. atomic number do not show the half-filled (5f7) electron subshell effect.