The crystallization kinetics of nanothin amorphous TlGa1 − x Ge x Se2 films

Crystallography Reports - The kinetics of phase transformations of amorphous Ge-doped TlGaSe2 films has been investigated by kinematic electron diffraction. It is shown that the crystallization of...     

The effects of annealing and rate of deposition on the electrical,optical and structural properties of amorphous GeSi alloy films

The electrical, optical and structural properties of rf-sputtered amorphous GeSi alloy films have been investigated as functions of the rate of deposition between 90 and 360 Å min^?1, and various annealing conditions. The stabilization evidenced in the electrical conductivity, optical absorption and density of these films deposited at higher rates and/or annealing temperatures may be explained in terms of the reduction of imperfections in the as-deposited films.     

Growth and structure of epitaxial Pb1 − x Mn x Se(Ga) films

The growth and structure of Pb_{1 ? x} Mn _x Se (Ga) (N_Ga = 0.8 at %) films with thicknesses of 0.3–0.5 μm, grown on single-crystal PbSe_{1 ? x} S _x (100) substrates by molecular-beam epitaxy, have been studied. It is established that films grow in a face-centered cubic lattice with the (100) orientation, reproducing the substrate orientation. The optimal conditions for obtaining photosensitive epitaxial films with perfect crystal structure are determined (W _1/2 = 70–80″).

     

Stoichiometry–structure correlation of epitaxial Ce1−xPrxO2−δ (x=0−1) thin films on Si(111)

Epitaxial oxide thin film layers are of interest for model catalytic studies. We report the growth of Ce_1?xPr_xO_2?δ mixed oxide layers of different stoichiometries (x=0–1) and oxygen deficiency (δ>0) on Si(111) by co-evaporating molecular beam epitaxy. The main objective is to identify the crystal phases and to investigate the correlation between compositions and crystal structures. X-ray photoemission spectroscopy was performed to quantify the stoichiometries. An extensive laboratory and synchrotron based X-ray diffraction analysis was carried out to determine the vertical and lateral lattice orientations and the strain status of the layers. The study revealed that single crystalline Ce_1?xPr_xO_2?δ/Si(111) heterostructures can be epitaxially grown on Si(111) for model catalytic studies. In addition to the structure–stoichiometry relationship typical to mixed oxide bulk powders, we identified a hexagonal mixed Ce–Pr oxide thin film phase not yet reported in bulk studies.     

Growth and structure of photosensitive Pb1−x Mn x Te(Ga) epitaxial films

The growth and structure of (1-1.5)-μm-thick Pb_1?x Mn _x Te(Ga)(x = 0.06) films with 0.4?0.9 at % of gallium, grown on BaF₂(111) and Pb_1?x Sn _x Te (x = 0.2) (100) substrates by molecular beam epitaxy, have been investigated. It is established that the films are crystallized into an fcc structure, and their growth planes are (111) and (100), according to the substrate orientation. The optimal conditions for obtaining high-resistivity photosensitive p-and n-type films with a perfect crystal structure (W _1/2 = 80″?100″) have been determined.     

Magnetic, magnetocaloric, and lattice properties of the La(Fe x Si1 − x )13 ferromagnets

The magnetic and lattice properties of a sample of La(Fe_0.86Si_0.14)₁₃ ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 × 10¹⁹ n/cm² increases the lattice constant a and the Curie temperature (T _C ) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(Fe _x Si_{1 ? x} )₁₃ compounds.     

Nature and origin of V-defects present in metalorganic vapor phase epitaxy-grown (InxAl1−x)N layers as a function of InN content,layer thickness and growth parameters

Our study of samples grown in different metalorganic chemical vapor deposition reactors and with different growth conditions reveals that V-pits are always present in (In_xAl_1?x)N films whatever the layer thickness and the InN content. V-pits are empty inverted pyramids terminating threading dislocations. InN-rich triangular regions are present around the threading dislocations terminated by pits with a hexagonal 6-fold symmetry distribution in {11?20} planes. The nature of the facets of the V-pits depends on the growth conditions: pits with either {11?2l}, l being between 1 and 3, or {1?101} facets have been observed. Moreover, the nature of the threading dislocations terminated by pits also depends on the growth conditions. Our observations suggest that with a high V/III ratio only edge a+c-type dislocations are terminated by pits whereas with a low V/III ratio both edge a-type and mixed a+c-type dislocations are terminated by pits.     

Composition dependence of the refractive index and its photo-induced variation in the binary glass systems: Ge1−xSex and As1−xSex

The composition dependence of the refractive index and its photo-induced variation have been calculated for the Ge_1?xSe_x and As_1?xSe_x binary glass systems, using the random network model. It is found that the refractive index has a minimum in Ge_1?xSe_x at x = 0.8, while it shows a monotomic increase with increasing As content in As_1?xSe_x glasses. The refractive index of the Ge_1?xSe_x system decreases with illumination and the variation Δn of GeSe₂ is ?0.0316, while the refractive index of the As_1?xSe_x system increases with illumination and the variation of As₂Se₃ is 0.01. These results are in agreement with the experimental results reported by several workers.     

X-Ray diffraction study of the evolution of phase and structural state and macroscopic stress during annealing of soft magnetic Fe95 − x Zr5N x films prepared by ion-plasma deposition

The evolution of the phase composition, nanostructure parameters, and macroscopic stress in soft magnetic Fe_{95 ? x} Zr₅N _x films (prepared by ion-plasma deposition onto quartz substrates) during their annealing has been investigated by X-ray diffraction. During deposition, depending on the N content, either a mixed structure composed of an X-ray amorphous phase enriched in Zr and N and a crystalline phase (α-Fe(N) solid solution) or an X-ray amorphous phase enriched in Fe, Zr, and N is formed in the films. During annealing, depending on the temperature and nitrogen content, different combinations of crystalline phases (α-Fe(N) and Zr(N) solid solutions, α-Fe, Fe₄N, Fe₂N, ZrO₂) are formed in the films. The large compressive stress formed in the films during deposition changes to a lower tensile stress during annealing.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x (R are rare earth elements) and their ordering: 5. A study of the ionic conductivity of as-grown Sr1 − x R x F2 + x crystals

Crystallography Reports - The ionic conductivity σ of Sr1 ? x R x F2 + x crystals (R = Y, La-Lu) has been measured in the temperature range of 324–933 K. The isomorphic...     

Effects of post-annealing temperature on structural,optical, and electrical properties of MgxZn1−xO films by RF magnetron sputtering

Mg_xZn_1?xO thin films were deposited on quartz substrates by RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated with the annealing temperatures increasing from 450 to 750 °C. The crystallinity of Mg_xZn_1?xO film annealed at 650 °C was significantly improved while the film annealed at 750 °C showed little improvement. The electrical properties degraded with the increase of annealing temperature. The annealing temperature seemed to impact the E_g value of Mg_xZn_1?xO thin films because of the variation of carrier concentration.     

Effect of Cd1−xZnxS/ZnS core/shell quantum dot on the optical response and relaxation behaviour of ferroelectric liquid crystal

Dielectrics, polarizing optical microscopic and electro-optical measurements have been carried out on a core/shell quantum dot Cd_1?xZn_xS/ZnS dispersed ferroelectric liquid crystal (FLC). In the present study, quantum dots were dispersed into two different concentrations of 0.1 and 0.25 wt./wt.% in pure FLC. The electro-optical parameters of pure and QDs dispersed FLC were carried out as a function of applied voltage. A significant improvement in optical response time of QDs dispersed FLC system is one of the major finding of the present study which may be useful for fabrication of faster liquid crystal system.     

Investigation of the structure and properties of (K x (NH4)1 − x )3H(SO4)2 single crystals

The influence of isomorphous replacement in the cation sublattice on the kinetics of the phase transition in single crystals of the solid solutions (K _x (NH₄)_{1 ? x} ) _m H _n (SO₄)_{(m + n)/2} · yH₂O belonging to the K₃H(SO₄)₂-(NH₄)₃H(SO₄)₂-H₂O salt system was studied. Superproton phase transitions for the end compositions of this system have been found earlier. The optical and thermal properties of crystals with the composition (K,NH₄)₃H(SO₄)₂ in the temperature range from 295 to 500 K were investigated, and the crystal structure was determined at 295 K. The results of the study and the comparison with the literature data show that the replacement of potassium atoms with ammonia leads to a fundamental change in the kinetics of the phase transition, the phase-transition temperature remaining virtually unchanged.     

Change of short-range order with temperature and composition in liquid GexSe1−x as shown by density measurements

Density measurements were performed on melts of the binary chalcogenide system Ge_xSe_1?x (0 ? x ? 0.5) up to 1000°C. The isotherm of molar volumes V_m at 750°C shows a relative maximum near GeSe₂. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. V_m's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range $\text{0 ? x ?}\text{1}\text{3}$ the short-range order at lower temperatures is determined mainly by $\text{GeSe}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range $\text{1}\text{3}\text{? x ? 0.5}$ the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe₂ and GeSe, the tendency of glass formation from the melt is discussed in detail.     

Investigation into the structure of ceramic Li x Na1−x Ta0.1Nb0.9O3 solid solutions by X-ray analysis and Raman spectroscopy

The structure of ceramic solid solutions Li _x Na_{1 ? x} Ta_0.1Nb_0.9O₃ has been investigated by full-profile X-ray diffraction analysis and Raman spectroscopy. It is shown that their structure for all x values is similar to the NaNbO₃ structure. The structure of NaTa_0.1Nb_0.9O₃ solid solutions (x = 0) is characterized by the sp. gr. Pbcm, and the structure of Li _x Na_{1 ? x} Ta_0.1Nb_0.9O₃ solid solutions with x = 0.05, 0.1, and 0.16 is characterized by the sp. gr. P2₁ ma. The unit-cell parameters decrease with an increase in x. At x = 0, doubled values of the parameter c and, correspondingly, the unit-cell volume are observed in the antiferroelectric phase. This fact is confirmed by the form of the vibrational spectrum in the region of stretching modes of oxygen atoms along the polar axis.     

The effect of Tb doped PbTiO3 inducing layer on texture and tunable property of sol–gel derived Pb0.4Sr0.6TiO3 thin films grown on ITO/glass substrate

Highly (1 0 0)-oriented Pb_0.4Sr_0.6TiO₃ (PST40) thin films have been prepared on the Tb doped PbTiO₃ (PTT) thin film coated ITO/glass substrate by sol–gel technique. The PTT inducing layers are (1 0 0)-oriented and can help to control the orientation of PST40 thin films. Crystallization of the PST40 thin film with the PTT inducing layer is more perfect than that without PTT layer due to less distortion in the thin film. The dielectric tunability of the PST40 thin film with PTT layer therefore reaches 65%, which is 85% higher than that without PTT layer. The dielectric loss of the PST thin film is only 0.05. These results indicate that (1 0 0)-oriented Tb doped PbTiO₃ can be used as an inducing layer for highly (1 0 0)-oriented tunable materials on ITO/glass substrate.     

Nanostructured crystals of the fluorite phases Sr1 − x R x F2 + x (R—rare-earth elements) and their ordering: II. Crystal structure of the ordered Sr4Lu3F17 phase

Crystallography Reports - The crystal structure of the ordered phase Sr4Lu3F17 prepared by directed crystallization of the melt has been investigated. The crystals have a trigonally distorted...     

The AC conductivity of superionic conducting glasses (AgI)x−(Ag4P2O7)1−x (x = 0.8, 0.75, 0.7): Experiment and analysis based on the generalized Langevin equation

The frequency-dependent complex impedance of superionic conducting glasses (AgI)_x − (Ag₄P₂O₇)_1−x (x = 0.3, 0.25, 0.20) was measured from 5 Hz to 500 kHz below room temperature. The frequency dependence of the conductivity and the electric modulus observed here cannot be expressed by a single relaxation equation, but it is well described by an equivalent circuit involving a contribution due to Jonscher's universal law σ [ω] ∼ ωⁿ (0 < n < 1). A linear relation between the DC conductivity and the relaxation time was observed irrespective of the sample compositions. These results are explained on the basis of the generalized Langevin equation associated with a non-exponential memory function. The physical basis of this approach is discussed in terms of the distribution of transition times arising from non-periodic potentials formed by immobile anions and many-body interactions among mobile cations at very high concentration in the superionic conducting glass.