Copper solubility and distribution in doped GaSb single crystals

For the GaSb single crystals doped with copper (grown using the Czochralski method without encapsulant in flowing atmosphere of hydrogen) the distribution coefficient of copper in GaSb,k _eff=0.0021±0.0006 was found and the copper solubility in GaSb was discussed. The region of copper solubility in GaSb was analyzed on the thermodynamic basis using chemical phase diagram in the Sb?Ga?Cu system. Due to a rather low solubility of copper, its excessive amount in GaSb caused probably an increase of the dislocation density at the end of the GaSb single crystals.     

Secondary emission of doped lithium hydride single crystals

Experimental studies of resonance Raman scattering (RRS) and of luminescence of excitons interacting with an impurity field and phonons in lithium hydride (LiH) crystals doped with Al, Mg, and Zn have been made. It has been shown that the presence of doped metal ions modifies the relaxation processes of excitons in the LiH lattice and gives rise to bound excitons with large and small radii.     

Radiation-stimulated aggregation of cationic vacancies in magnesium oxide single crystals

Conclusions We have observed and studied the aggregation of cation vacancies in irradiated single crjrstals of magnesium oxide containing hydroxyl ions, using EPR, TSL, and optical spectroscopy. The appearance of V centers that have an anomalously high thermal stability has been demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 745–750, April, 1986.     

Electron paramagnetic resonance study of vanadyl doped in zinc maleate tetrahydrate single crystals

Spectroscopy of vanadyl doped zinc meleate tetrahydrate single crystals has been studied by EPR in the X-band frequencies (∼9.5 GHz) and optical spectra. It is found that vanadium enters the zinc host lattice substitutionally.     

Non-covalent intermolecular interactions of colloidal nematic liquid crystals doped with graphene oxide

Graphene oxide (GO) was doped to eutectic uniaxial nematic liquid crystals (NLCs) (E_5CN7) with different percentages to improve the physiochemical properties of NLCs effectively. GO shifts the N-I phase transition temperature to higher values. It has been observed that increasing GO concentration up to 0.75% increases the N-I phase transition temperature substantially while further increase of GO concentration results in an inverse trend. The GO/E_5CN7 non-covalent interactions change the N-I phase transition. The contribution of several terms such as anchoring and polarisation effects on N-I phase transition was quantified as well. The results suggest that the size is an important contributor to GO and liquid crystal interaction. The results show that E_5CN7@GO composites may act as promising candidates to enhance the efficiency of room temperature devices.     

Morphological and dimensional control via hierarchical assembly of doped oligoaniline single crystals

Single crystals of doped aniline oligomers are produced via a simple solution-based self-assembly method. Detailed mechanistic studies reveal that crystals of different morphologies and dimensions can be produced by a "bottom-up" hierarchical assembly where structures such as one-dimensional (1-D) nanofibers can be aggregated into higher order architectures. A large variety of crystalline nanostructures including 1-D nanofibers and nanowires, 2-D nanoribbons and nanosheets, 3-D nanoplates, stacked sheets, nanoflowers, porous networks, hollow spheres, and twisted coils can be obtained by controlling the nucleation of the crystals and the non-covalent interactions between the doped oligomers. These nanoscale crystals exhibit enhanced conductivity compared to their bulk counterparts as well as interesting structure-property relationships such as shape-dependent crystallinity. Furthermore, the morphology and dimension of these structures can be largely rationalized and predicted by monitoring molecule-solvent interactions via absorption studies. Using doped tetraaniline as a model system, the results and strategies presented here provide insight into the general scheme of shape and size control for organic materials.     

Heat capacity of pure and doped V2O3 single crystals

Heat capacities have been measured for single crystals of V₂O₃, either pure or doped with 1 and 1.4 mole% Cr₂O₃ and Al₂O₃ over the temperature range 100–700°K. V₂O₃ undergoes a fairly sharp transition at low temperatures (～170°K) but fails to exhibit any thermal anomaly above 300°K. The thermal behavior of (M_xV_1?x)₂O₃, M = Cr, Al, is manifested by two transitions: one at low temperatures, 170–180°K for x = 0.01 and 180–190°K for x = 0.014, and the other at high temperatures. For x = 0.01, the high-temperature (HT) anomaly extended over the range 325–345°K (Cr-doped V₂O₃) and 345–365°K (Al-doped V₂O₃), respectively. The corresponding ranges for x = 0.014 were found to be 260–280°K and 270–290°K, respectively. Further, the HT anomaly was characterized by a large hysteresis (～50°K). The values of lattice heat capacity of pure and doped V₂O₃ were, however, found to be almost the same and could be empirically represented by the Debye (D)?Einstein (E) function $\text{D}\text{(}\text{580}\text{T}\text{) + 4}\text{E}\text{(}\text{θ}\text{T}\text{)}$ with θ values 430°K (T = 100–230°K) and 465°K (T > 230°K), respectively. Further, the enthalpy change ΔH associated with the HT anomaly in doped V₂O₃ (80 ≤ ΔH ≤ 510 J/mole) was 5–10 times smaller than the ΔH corresponding to the lower-temperature transition. The results cited here appear incompatible with the Mott transition model that has been invoked to explain the HT anomaly.     

Behavior under gamma irradiation of single crystals of NaCl doped with divalent cations

Thermally stimulated luminescence and optical absorption measurements were performed on NaCl single crystals, both single and double doped. The NaCl single crystals were exposed to gamma rays from a ⁶⁰Co source at both low and room temperatures. The radiation-induced defects were mainly F and H centers, and the absorption bands for the F centers were centered at 464 nm. Bleaching with F-light showed the participation of the F center generated by gamma radiation on the TL phenomenon. The results suggest that NaCl single crystals, both single and double doped can be used as dosimeters, within certain doses.     

ESR and optical study of Mn2+ doped ammonium selenate single crystals

ESR and optical absorption studies of manganese doped ammonium selenate single crystals are performed at X-band and room temperature to ascertain the site symmetry and location of impurity ions in the lattice. Manganese ions are expected to enter the lattice interstitially. Various spin Hamiltonian parameters are determined. Optical absorption study is also done and associated distortion in the crystal lattice is estimated.     

EPR and optical study of Mn2+ doped ammonium tartrate single crystals

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.     

Poly(decamethylene oxide) single crystals from dilute solution

Summary A preliminary study on the morphology and chain orientation of four low molecular weight poly(decamethylene oxide) fractions crystallized from ethyl alcohol diluted solution is reported. The single crystals predominantly show the polyethylene orthorhombic unit cell projection although some also present the polytetrahydrofuran structure. The characteristic X-ray long periods obtained are indicative in all cases of a chain folded crystal surface.

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Zusammenfassung Eine vorläufige Studie der Morphologie und der Kettenorientierung von vier Polydecamethylenoxyd-Fraktionen niederen Molekulargewichtes, die aus verdünnter Methylalkohol-Lösung kristallisiert wurden, wird wiedergegeben.Die Einzelkristalle zeigen bevorzugt die orthorhombische Projektion der Einheitszelle, obgleich einige auch die Polytetrahydrofuranstruktur präsentieren. Die charakteristischen Röntgenstrahllangperioden deuten in allen Fällen auf eine kettengefaltete Kristalloberfläche hin.

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With 5 figures

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Thanks are due to Mr.J. Tinas Gálvez for the kind supply of the samples.     

Morphology of single-chain single crystals of poly(ethylene oxide)

Single-chain particles of poly(ethylene oxide) (PEO) were prepared by spreading a 10^-4 wt.-% solution of PEO in benzene on a hot water surface. After isothermal crystallization at 317,2 ± 0,1 K for 10 h, regular-shaped single-chain crystals were observed. A variety of typical morphologies were also found, and some of them are discussed on the basis of the habit of PEO crystals and various twin modes.     

Determination of impurities in single crystals of magnesium oxide by neutron activation analysis

The determination of some trace impurities in single-crystal magnesium oxide is described. Radiochemical separations of iron, cobalt, scandium, manganese and chromium by ion exchange and solvent extraction are applied in conjunction with γ-spectrometry. The impurities that give rise to long-lived γ-emitting isotopes are considered.     

Investigation of the fold-surface problem in polyethylene single crystals with the nitric acid oxidation technique

Single-crystal preparations of polyethylene were treated with the selective oxidizing agent, fuming nitric acid. The degraded products were examined as regards layer thickness (by low-angle x-ray studies), chemical and weight changes, recrystallization and annealing treatments, and by broadline NMR, as part of a systematic investigation aimed at clarifying the nature of disordered material in single crystals. It emerges that there is a disordered-mobile region along the fold surface of the crystals in agreement with other parallel works along similar lines. In a more detailed analysis we can now decompose the nitric acid attack into components affecting the basal and side surfaces, respectively. Taking into account the recrystallization–annealing observations, we infer that the fold surface is heterogeneous with folds of more than one kind. These results were combined with a preliminary molecular weight distribution study by gel permeation chromatography. Taking into account all the available evidence, we are led to suggest a composite structure where surface looseness, coresponding to long loops and hairs, is superimposed on the more regular folded surface. This model is in the process of being tested. The problems concerning the assignment of a value to the amount of surface looseness are being discussed. In addition, a discontinuity in the thermal behavior of the crystals between 75 and 80°C. has been detected.     

Optical properties of perturbed NO 2 − ions in KNO2 doped NaNO2 single crystals

Summary On the basis of high-resolution and time-resolved fluorescence spectra, a model is proposed for the interpretation of the fluorescence lines originating from various perturbed NO ₂ ^– centers situated in the neighbourhood of the K⁺ ion of the NaNO₂:KNO₂ crystal. Since their excited state energies are lower than that of the host, these perturbed NO ₂ ^– ions act as traps for the host singlet exciton. On the assumption that the perturbation giving rise to those traps results from an interaction of the impurity ion K⁺ with its nearest neighbours, the observed position of the energy levels of the various traps can be reconciled with crystal field calculations.