Search results for "Cubic crystal system"
showing 9 items of 49 documents
Ferroelastic transition in Kbr:Kcn studied by neutrons, x-rays and ultrasonic
1986
The ferroelastic phase transition of (KBr) 0 27 (KNC) 0.73 has been studied by X-ray diffraction, ultrasonics and inelastic neutron scattering. It is the first example of a cubic crystal where the elastic shear constant C 44 softens completely corresponding to the m = 2 universality class. C 44 and the Bragg intensities show a non-classical critical behaviour.
Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl-Protected Body-Centered Cubic Clus…
2016
The synthesis, structure, substitution chemistry, and optical properties of the gold-centered cubic monocationic cluster [Au@Ag8@Au6(C≡CtBu)12]+ are reported. The metal framework of this cluster can be described as a fragment of a body-centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [MnAg8−nAu7(C≡CtBu)12]+ clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [CunAg8Au7−n(C≡CtBu)12]+ clusters (n=1–6), with the Cu atom(s) presumably occup…
Surface order in body-centered cubic alloys
1993
Free (100)-surfaces of body-centered cubic binary alloys are studied in a parameter range where the bulk turns from the ordered B2-phase to the disordered A2-phase. A model is chosen that describes iron-aluminium alloys in a fairly realistic way. Mean field treatments and Monte Carlo investigations both show that under certain circumstances the surface remains ordered far above the bulk disordering temperatureT c, though the surface order parameter and the surface susceptibility exhibit a singularity atT c with critical exponents characteristic for the ordinary transition. One finds, that if the surface is nonstoechiometric and different layers are not equivalent with respect to perfect bul…
Surface-induced ordering and disordering in face-centered-cubic alloys: A Monte Carlo study
1996
Using extensive Monte Carlo simulations we have studied phase transitions in a fcc model with antiferromagnetic nearest-neighbor couplings $J$ in the presence of different free surfaces which lead either to surface-induced order or to surface-induced disorder. Our model is a prototype for CuAu-type ordering alloys and shows a strong first-order bulk transition at a temperature $\frac{k{T}_{\mathrm{cb}}}{|J|}=1.738005(50)$. For free (100) surfaces, we find a continuous surface transition at a temperature ${T}_{\mathrm{cs}}g{T}_{\mathrm{cb}}$ exhibiting critical exponents of the two-dimensional Ising model. Surface-induced ordering occurs as the temperature approaches ${T}_{\mathrm{cb}}$ and …
Monte Carlo studies of anisotropic surface tension and interfacial roughening in the three-dimensional Ising model.
1989
Extensive Monte Carlo simulations of the simple cubic Ising model with nearest-neighbor ferromagnetic interactions with a tilted interface are presented for a wide range of lattice size L, temperature T, and tilt angles \ensuremath{\theta}. The anisotropic interfacial tension is studied in detail. From the small-angle data, we obtain the step free energy density ${f}_{S}$(T,L). Finite-size scaling of the step free energy density is discussed and used to probe the predicted temperature dependence of the correlation length near and above the roughening transition. The square-root temperature dependence predicted by solid-on-solid model calculations is exhibited. Finite-size scaling implies th…
Self-assembled MgxZn1−xO quantum dots (0 ≤ x ≤ 1) on different substrates using spray pyrolysis methodology
2013
By using the spray pyrolysis methodology in its classical configuration we have grown self-assembled MgxZn1−xO quantum dots (size [similar]4–6 nm) in the overall range of compositions 0 ≤ x ≤ 1 on c-sapphire, Si (100) and quartz substrates. Composition of the quantum dots was determined by means of transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy. Selected area electron diffraction reveals the growth of single phase hexagonal MgxZn1−xO quantum dots with composition 0 ≤ x ≤ 0.32 by using a nominal concentration of Mg in the range 0 to 45%. Onset of Mg concentration about 50% (nominal) forces the hexagonal lattice to undergo a p…
Magnetoresistivity and crystal structure of epitaxial La0.67Ca0.33MnO3 films
1998
Abstract We investigated thin-film growth of doped manganites by sputter deposition on SrTiO 3 (1 0 0), MgO (1 0 0) and r -plane Al 2 O 3 (1 0 1¯2) substrates and found an in-plane-oriented growth. The unit cell of the films showed distortions from the simple cubic perovskite structure, represented by a tetragonal unit cell with a′ = b′ = √2 a ; c′ = 2 a . By scanning electron microscopy we investigated the growth morphology of the films. We determined the magnetotransport properties above and below room temperature. Transport at high temperatures is best described by polaron hopping.
Fabrication of Robust High-Quality ORMOCER® Inverse Opals
2006
The nanostructuring of ORMOCER® to form inverse opals is described. For this purpose a polymer opal is used as a template and infiltrated with liquid ORMOCER®. After photopolymerization of the resin the host opal is dissolved in tetrahydrofuran and an ORMOCER® inverse opal is obtained. It shows excellent periodicity (by SEM) and optical properties to reveal a high degree of face centered cubic order. This replication process leads to a nanostructured photonic crystal with the outstanding mechanical properties of ORMOCER® and high temperature stability up to 350 °C.
Solubility-Driven Isolation of a Metastable Nonagold Cluster with Body-Centered Cubic Structure.
2020
The conventional synthetic methodology of atomically precise gold nanoclusters using reduction in solutions offers only thermodynamically most stable nanoclusters. We report herein a solubility‐driven isolation strategy to access the synthesis of a metastable gold cluster. The cluster, with the composition of [Au 9 (PPh 3 ) 8 ] + ( 1 ), displays an unusual, nearly perfect body‐centered‐cubic (bcc) structure. As revealed by ESI‐MS and UV/Vis measurement, the cluster is metastable in solution and converts to the well‐known [Au 11 (PPh 3 ) 8 Cl 2 ] + ( 2 ) within just 90 min. DFT calculations revealed that while both 1 and 2 are eight‐electron superatoms, there is a driving force to convert 1 …