Synthesis and native defectivity of Zn1−x V x O (0 ≤ x ≤ 0.03) photocatalysts

Nanodisperse solid solutions Zn_1?x V _x O (0 ≤ x ≤ 0.03) with high numbers of defects in an oxygen sublattice are synthesized via the precursor technique. ESR analysis reveals that V _O ⁺ oxygen vacancies are the main defects of the oxygen sublattice in the Zn_1?x V _x O structure. The Zn_1?x V _x O (0 < x ≤ 0.15) solid solutions exhibit high photocatalytic activity during hydroquinone oxidation in water upon irradiation with UV and visible light.     

Separation of magnetic phases in La1 − x CaxMnO3 manganites with 0.6 ≤ x ≤ 0.9

The magnetic properties of La_{1 ? x} Ca_xMnO₃ solid solutions were studied in wide temperature and magnetic field ranges, T = 2–600 K and H ≤ 50 kOe. Semiconducting compositions with 0.6 < × < 0.9 exhibited an unusual temperature behavior of magnetization and susceptibility with well-defined Curie and Néel temperatures. The simultaneous manifestation of both ferromagnetic and antiferromagnetic properties is evidence of the coexistence of two collinear magnetic phases. The content of impurity ions was shown to have a strong influence on the T _C and T _N values, whereas the ratio between the ferro-and antiferromagnetic phase volumes heavily depended on thermal treatment conditions. The magnetic properties of the whole series of La_{1 ? x} Ca_xMnO₃ solid solutions can be explained in terms of the phase separation model.     

Features of magnetic properties of La x MnO3 + δ (0.815 ≤ x ≤ 1.0)

Magnetic and resonance studies of the system of polycrystalline samples of self-doped manganites La _x MnO_{3 + δ} (x = 0.815, 0.90, 0.94, 0.97, and 1.0) have been performed in a temperature range of 77–300 K. According to ⁵⁵Mn NMR data, all samples contain a ferromagnetic phase at 77 K. As the defect density increases (x changes from 1.0 to 0.815), samples become more magnetically ordered. In this case, the ferromagnetic state of the system gradually changes from a mixed state in which both ferromagnetic insulating (basic) and ferromagnetic metal (for x = 0.97 and 1.0) phases coexist to only the ferromagnetic metal state (for x = 0.815 and 0.90). It has been shown that both ferromagnetic metal and ferromagnetic insulating phases are inhomogeneous, and either phase consists of two phases with different dynamics of nuclear spins and different Curie temperatures. The diagram of the magnetic phase state of the La _x MnO_{3 + δ} system (x = 0.815, 0.90, 0.94, 0.97, 1.0) has been constructed for a temperature range of 120–240 K and Mn⁴⁺ contents of 12–30%.     

Structural deformations in metastable cubic compounds Ni(1 − x)Zn x O (0.60 ≤ x ≤ 0.99)

X-ray diffraction has been used for studying the fine crystal structure of metastable cubic oxide compounds Ni_{(1 ? x)}Zn _x O (0.60 ≤ x ≤ 0.99) obtained from the initial hexagonal phase by quenching of the samples at a high temperature and under external hydrostatic pressure. It has been found that the diffraction patterns of these compounds include a system of diffuse superstructure maxima, whose number and intensity essentially depend on the composition. The origin of this superstructure has been discussed.     

Cation disorder and structural studies on Bi4−x Nd x Ti3O12 (0.0≤x≤2.0)

Here we report the results of combined powder X-ray and neutron diffraction studies of Bi_4?x Nd _x Ti₃O₁₂ (0.0 ≤ x ≤ 2.0) compositions. The parent Bi₄Ti₃O₁₂ has an orthorhombic lattice (space group: B2cb) with unit cell parameters a = 5.4432(5) Å, b = 5.4099(5) Å and c = 32.821(2) Å, and V = 966.5(1) ų. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd³⁺ ion concentration with a discontinuity at x = 0.75. Orthorhombicity of the lattice decreases with increase in Nd³⁺ content in the lattice. The orthorhombic unit cell parameters for a representative Bi₂Nd₂Ti₃O₁₂ composition are: a = 5.3834(9), b = 5.3846(9) and c = 32.784(1) Å. The observed orthorhombic distortion at x = 2.0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd³⁺ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd³⁺ in the fluorite slab increases with increase in Nd³⁺ contents.     

Fine structure and magnetism of bulk Zn1 − x Cr x Se single-crystal cubic compounds (0 ≤ x ≤ 0.045)

The character of structural and magnetic features of the cubic lattice of bulk Zn_{1 ? x} Cr _x Se crystals (0 ≤ x ≤ 0.045) has been investigated using thermal neutron diffraction and magnetic measurements. It has been found that the diffraction scans of doped crystals contain effects of nuclear diffuse scattering caused by local static atomic displacements in the face-centered cubic (fcc) lattice. Results of magnetic measurements of doped crystals indicate the presence of weak antiferromagnetic correlations, which are a consequence of structural features of these compounds.     

The influence of praseodymium concentration on the luminescence properties of Ca1 ? x Pr x F2 + x (0.002 ≤ x ≤0.35)

The possibility of implementing photon cascade emission in CaF₂-PrF₃ crystals by increasing the PrF₃ concentration in the CaF₂ matrix is studied. It is shown that an increase in the Pr³⁺ content leads to redistribution of radiative transitions in favor of the ¹ S ₀-luminescence. The decrease in the efficiency of the second step of photon cascade emission at high PrF₃ concentrations is caused by quenching of the ³ P ₀ ?? 4f ² transitions as a result of cross relaxation.     

Phase stratification in the Nd1 − x BaxCoO3 − δ (0.3 ≤ x ≤ 0.54) system

Slowly cooled Nd_{1 ? x} Ba_xCoO_{3 ? δ} samples were two-phase in the concentration interval 0.3 ≤ x ≤ 0.46. One of the phases had O-orthorhombic lattice distortions (Pbnm) characteristic of ferromagnetic samples with x ≤ 0.3, and the other phase had tetragonal distortions (P4/mmm) characteristic of samples with x ≥ 0.46. Tetragonal distortions were caused by ordering of Nd³⁺ and Ba²⁺ ions. Samples with ordered neodymium and barium ions (Nd_{1 ? y} Ba_{1 + y} Co₂O_{6 ? γ} at ?0.08 ≤ y ≤ 0.08) experienced metal-dielectric and orientation magnetic phase transitions.     

Superconductivity,crystallization, and structural relaxation of the new metallic glass system La1−x Si x (0.15≤x≤0.27)

New metallic glass alloys have been prepared by melt spinning of La–Si samples in a pumped system. The superconducting transition temperature,T _c , increases linearly with the La concentration, from 3.00 K at 73 at. % La to 3.80 K at 85 at. %. Three new metastable phases: -, -, and -La₃Si, were formed by annealing and crystallizing amorphous La₃Si. Their crystal structures are orthorhombic (a=6.32 Å,b=8.06 Å,c=9.96 Å), hcp (a=10.55 Å,c=5.05 Å), and tetragonal (a=6.92 Å,c=5.05 Å) resp.T _c increased to 3.75 K, 6.00 K and 6.80 K, resp. During low temperature anneals of an amorphous La₃Si alloy,T _c changed logarithmically with time.On leave from Institute of Physics, Academica Sinica, Beijing, China     

An anomaly in the magnetic susceptibility of the Mg1−x CuxO solid solutions with 0.01≤x≤0.20

The problem of localized superconductivity has motivated the preparation of Mg_1−x Cu_xO solid solutions with NaCl structure and 0.01≤x≤0.20, as well as a study of the magnetization and magnetic susceptibility χ in the 2–400 K temperature range and in magnetic fields of up to 5 T. The temperature dependence of χ is described for all compositions by the Curie-Weiss law, χ = C/(T − θ), where the constant C is close to the value calculated for each composition for μ_eff = 1.7–1.9μ_B, and θ is close to zero. For T < 30 K, χ(T) deviates for all compositions toward lower χ, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T∼320–330 K, an anomaly of a diamagnetic type, i.e., a decrease of χ by 6–30% of its paramagnetic value, has been observed for all compositions against the background of the generally paramagnetic χ(T). A discussion is presented of alternative reasons for this anomaly and of its possible connection with localized superconductivity. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 4, 2000, pp. 701–703. Original Russian Text Copyright ? 2000 by Samokhvalov, Arbuzova, Viglin, Naumov, Smolyak, Korolev, Lobachevskaya.     

Zn1−x Mg x O (0≤x≤0.05) nanowalls grown on catalyst-free sapphire substrates by high-pressure PLD and their photoluminescence properties

We report the growth of Zn_1?x Mg _x O (x=0, 0.02, 0.05 at.%) nanowalls on sapphire substrates without any metal catalysts by a high-pressure pulsed laser deposition (PLD). The influences of the experimental parameters like growth pressure, temperature, and target-substrate distance on the growth of Zn_1?x Mg _x O nanowalls were systemically studied and the growth mechanism was discussed. It was found that large area and uniform Zn_1?x Mg _x O nanowalls with c-orientation can be grown on sapphire substrates when the growth temperature and pressure were 950 °C and 400 Torr at a target-substrate distance of 2 cm. A thin layer assisted vapor-solid (VS) process was proposed for Zn_1?x Mg _x O nanowalls growth. The photoluminescence spectrum shows the bandgap of Zn_1?x Mg _x O nanowall was effectively expanded together with defect-related levels formation in a forbidden gap, which also induced enhancement of visible emission.     

Luminescence properties of Sr3−x−3y/2MxCeyAlO4F (M=Ca,Ba, 0≤x≤0.9, 0.001≤y≤0.05) phosphors

Luminescent materials composed of Sr_3?x?3y/2M_xCe_yAlO₄F (M=Ca, Ba, 0≤x≤0.9, 0.001≤y≤0.05) were prepared by the solid-state reaction method. X-ray diffraction (XRD) patterns of the obtained oxyfluorides are exhibited for indexing peak positions. Dynamic excitation and emission spectra of the Ce³⁺-activated oxyfluoride phosphors are clearly monitored. The critical emission quenching as a function of Ce³⁺ contents in Sr_2.5?3y/2M_0.5Ce_yAlO₄F phosphors is revealed at quite low concentrations of the activator. CIE coordinates of blue and green Sr_2.5?3y/2M_0.5Ce_yAlO₄F phosphors are clearly measured. The relative quantum efficiency of Sr_2.4985Ca_0.5Ce_0.005AlO₄F based on the integrated emission is determined. The Sr_3?x?3y/2M_xCe_yAlO₄F phosphors excited near 410 nm light could be prominent phosphors in applications of NUV-LED.     

Hyperfine fields and magnetic anisotropy in Fe1000−x Gd x thin films and Fe80−x GdxB20(0≤x≤24) thin films and ribbons

The Mössbauer measurements performed on Fe_100–x Gd _x thin films and on Fe_80–x Gd _x B₂₀ both as thin films and ribbons show a dependence of the spins orientation and H_hyp versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and H_hyp decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.     

Pr1—xKxMnO3（0.0≤x≤0.15）的化学键性质研究

采用半经验的复杂晶体化学键理论研究了ｒ１－ｘＫｘＭｎＯ３的化学键性质。计算结果表明，Ｐｒ－Ｏ键及Ｋ－Ｏ的共价性随钾掺杂浓度的增加而略有减小，Ｍｎ－Ｏ的共价性则增加，且Ｍｎ－Ｏ的共价性要强于Ｐｒ（Ｋ）－Ｏ键，得到的键极化率也服从同样的规律。     

Electronic States near the Fermi Level in the Antiferromagnetic and Ferromagnetic Spinels of Zn 1− x Cu x Cr 2 Se 4 ; 0.0 ≤ x ≤ 1.0

The electronic states of normal-type spinels in Zn 1 m x Cu x Cr 2 Se 4 have been studied by X-ray absorption spectroscopy near the K-edge of Zn, Cu, Cr and Se ions. It is found that characteristic white lines occur near the X-ray absorption threshold for Zn and Se ions, but not for Cu and Cr ions. It is also found that the white lines show a slight energy shift, which depends on the Cu concentration. The energy shifts mean that Fermi level gradually approaches the top region of the valence band of Se 2 m , on increasing the Cu ions. The substitution of Zn 2+ with Cu 1+ ions increases the number of positive carriers, holes. The holes occupying the top region of the valence band strongly correlate with Cr 4+ , which forms an empty orbital in the 3d-band of Cr 3+ and exchanges the valence electrons with Cr 3+ . It is interpreted that the ferromagnetism in Zn 1 m x Cu x Cr 2 Se 4 is made by double-exchange interaction between Cr 3+ and Cr 4+ ions and that holes contribute to the electronic conductivity of Zn 1 m x Cu x Cr 2 Se 4 .     

Effect of Nd doping on the magnetic properties of charge-ordered Bi0.6−x Nd x Ca0.4MnO3 (0.0≤x≤0.6) perovskite manganites

We have studied structure, magnetic and transport properties of polycrystalline Bi_0.6?x Nd _x Ca_0.4MnO₃ (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6). Substitution of Nd at Bi sites induces a strong interplay between the magnetic and charge ordering. The charge-ordering temperature (T _CO) decreases with increasing x. Further, the antiferromagnetic ordering temperature (T _N) increases sharply at both extremes and remains nearly constant for x=0.2–0.4. At T<T _N a transition to a metamagnetic glass-like state is also seen. Nd doping also leads to enhancement in the magnetic moment and a concomitant decrease in resistivity up to x=0.3 and then an increase in resistivity up to x=0.5. Furthermore, Nd doping promotes an antiferromagnetic to ferromagnetic type fluctuation in the materials at room temperature, as evidenced by the change in the value of the paramagnetic Curie temperature. We find that the local lattice distortion induced by the size mismatch between the A-site cations and the 6s² character of Bi³⁺ lone pair electrons explains the observed peculiarity in magnetic and transport properties of Nd-doped Bi_0.6Ca_0.4MnO₃.     

La0.67-xSmxSr0.33MnO3(0.40≤x≤0.60)体系的TCR研究

通过测量La0.67-xSmxSr0.33MnO3(x=0.40,0.50,0.60)体系的M～T曲线和ρ～T曲线,研究了La位Sm掺杂对体系电阻温度系数 (TCR)的影响.实验结果表明:Sm掺杂引起的电阻率曲线急剧变化,导致大的TCR出现;TCR在x=0.40时出现峰值,随Sm掺杂的增加,TCR值逐渐减小.体系出现大的TCR,来源于Sm掺杂引起的晶格畸变和额外磁性.     

Transport properties of the single-crystal La2−xBaxCuO4 (0≤x≤0.11)

We report on the temperature dependence of the in-plane electrical resistivity ρ_ab and the in-plane Hall coefficient R_H in various magnetic fields of the single-crystal La_2−xBa_xCuO₄ with x=0.083 and 0.11. In x=0.11, which is close to x=1/8, where the superconductivity is strongly suppressed, a clear jump in ρ_ab and a drop in R_H have been observed at T_d2∼53 K, where the structural phase transition between the orthorhombic mid-temperature and tetragonal low-temperature phases occurs. Moreover, a sign reversal of R_H has been observed below ∼25 K and the magnitude of the sign reversal increases with increasing magnetic field. In x=0.083, on the other hand, there is neither jump in ρ_ab nor drop in R_H at T_d2, and also no sign reversal in R_H at low temperatures even in magnetic fields up to 9 T. In conclusion, there is no doubt that a static stripe order of holes and spins, observed in La_1.6−xNd_0.4Sr_xCuO₄ with x∼1/8, is formed below T_d2 also in La_2−xBa_xCuO₄ with x∼1/8. The R_H in the stripe-ordered state has a negative value, which is consistent with the recent theory by Prelovšek et al.     

Ellipsometry study of interband transitions in TlGaS2xSe2(1−x) mixed crystals (0≤x≤1)

In this paper, the spectroscopic ellipsometry measurements on TlGaS_2xSe_2(1?x) mixed crystals (0≤x≤1) were carried out on the layer-plane (001) surfaces with light polarization E⊥c^? in the 1.2–6.2 eV spectral range at room temperature. The real and imaginary parts of the dielectric function, refractive index and extinction coefficient were calculated from ellipsometric data using the ambient-substrate optical model. The critical point energies in the above-band gap energy range have been obtained from the second derivative spectra of the dielectric function. Particularly for TlGaSe₂ crystals, the determined critical point energies were assigned tentatively to interband transitions using the available electronic energy band structure. The effect of the isomorphic anion substitution (sulfur for selenium) on critical point energies in TlGaS_2xSe_2(1?x) mixed crystals was established.