Materials Literature
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We present an approach to electronic polarization in molecular solids treated as a set of quantum systems interacting classically. Individual molecules are dealt with rigorously as quantum-mechanical systems subject to classical external fields created by all other molecules and, possibly, external sources. Self-consi…
We report unambiguous experimental evidence for an achiral orthogonal biaxial smectic-A phase which exhibits antiferroelectric switching behavior. The evidence is based on x-ray-diffraction measurements, texture observation, and the results of dielectric and electro-optical measurements.
Equations are proposed for computing from ab initio wave functions quantities like 〈SA⋅SB〉, which appear in the Heisenberg model Hamiltonian of magnetism. These equations are based on projection operators derived from Löwdin orthogonalization. They result in local spin operators SA which obey the definition of angular…
The crystal structures of Bi4Ti3O12 and Bi3.25La0.75Ti3O12 were refined by neutron powder diffraction. Large structural distortions were revealed, and ferroelectric polarizations along the a and c axes were calculated from the displacements of the constituent ions. In Bi3.25La0.75Ti3O12, La atoms substitute for Bi ato…
We report the magnetization and the susceptibility measurements of the RuSr_2GdCu_2O_y and RuSr_2NdCu_2O_x perovskite materials. We find that RuSr_2GdCu_2O_y compound exhibits a magnetic transition at Tn=135 K followed by a superconducting one with an onset Tc=35 K. Samples of RuSr_2NdCu_2O_x material have shown neith…
First-principles density-functional calculations within the local-density approximation and the pseudopotential approach are used to study and characterize the ferroelastic phase transition in calcium chloride (CaCl_2). In accord with experiment, the energy map of CaCl_2 has the typical features of a pseudoproper ferr…
The energy radiated by moving cracks in a discrete background is analyzed. The energy flow through a given surface is expressed in terms of a generalized Poynting vector. The velocity of the crack is determined by the radiation by the crack tip. The radiation becomes more isotropic as the crack velocity approaches the…
The out-of-equilibrium low-frequency complex susceptibility of the orientational glass methanol(73%)-beta-hydrochinone-clathrate is studied using temperature-stop protocols in aging experiments . Although the material does not have a sharp glass transition aging effects including rejuvenation and memory are found at l…
A combined study with use of time-domain pump-probe spectroscopy and time-domain terahertz transmission spectroscopy have been carried out on an underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ thin film. It was observed that the low energy multi-excitation states were decomposed into superconducting gap and pseudogap. The ps…
We report a detailed study of the electronic structure of the MgB$_{2}$ with different lattice constants by using the full-potential linearized augmented plane wave(FPLAPW) method. It is found that the lattice parameters have great effect on the $σ$ band of Boron. Our results indicate that increasing lattice constant…
Ionic-pair equal-time displacement correlations in relaxor lead magnesium niobate, $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3},$ have been investigated at 300, 270, and 240 K in terms of an x-ray diffuse scattering technique. Functions of the distinct correlations have been determined quantita…
A beautiful and intriguing relationship has recently been proposed to express the critical screening lengths associated with the apparition of new bound states for the two-dimensional statically screened Coulomb potential. Semiclassical quantum theory show that this relationship is unfortunately not strictly exact. Th…
A modeling of the soil structure and surface roughness by means of the concepts of the fractal growth is presented. Two parameters are used to control the model: the fragmentation dimension, $D_f$, and the maximum mass of the deposited aggregates, $M_{max}$. The fragmentation dimension is related to the particle size…
We report valence and conduction band alignments and offsets for heterojunctions between CdCr2Se4, an n-type ferromagnetic semiconductor, and the non-magnetic materials Si and GaAs, evaluated using density functional theory. We explore numerically the impact of different interface features on the type of band alignmen…
Ab initio calculations are performed to elucidate the mechanism of the photoisomerization of azobenzene. We obtain the excitation energies of the S1(n→π*), S2(π→π*), and S3(n2→π*2) states by complete active space self-consistent field (CASSCF) and multireference single double configuration interaction (MRSDCI) calcula…
Thin films of CrSb grown by solid-source molecular-beam epitaxy on GaAs, (Al, Ga)Sb, and GaSb are found to exhibit ferromagnetism. Reflection high-energy electron diffraction and high-resolution cross sectional transmission electron microscopy both indicate that the structure is zincblende. Temperature dependence of r…
Thorough Raman and infrared (IR) reflectivity investigations of nominally pure ${\mathrm{SrTiO}}_{3}$ ceramics in the 10--300 K range have revealed a clear presence of the polar phase whose manifestation steeply increases on cooling. The Raman strengths of the Raman-forbidden IR modes are proportional to ${\ensuremath…
The crystal structure of 3-picoline (3-methylpyridine, C6H7N) has been determined at 120 (2) K following in situ crystal growth from the liquid. The molecules pack in a herring-bone-type arrangement in the non-centrosymmetric space group Pna21.
TEM analyses enable a priori investigation of smectic bilayer structures in an amorphous−liquid crystalline (LC) diblock copolymer. A newly synthesized copolymer with 85 wt % LC phase segregates into a layered morphology in both bulk and thin film studies. The microstructure has a periodicity of ∼70 Å and forms highly…
Computer simulations of systems of soft repulsive spherocylinders (SRS) of aspect ratio (L/D) equal to 4 have been carried out using the parallel molecular dynamics program GBMOLDD. At sufficiently high densities the system forms stable nematic and smectic-A liquid crystalline phases. Results are presented for a serie…