铌酸锶钡晶体的光存储实验研究

通过全息存储光路调整,采用适当的曝光时间,在铌酸锶钡晶体中得到清晰的全息存储图象,并通过高压固化存储图象,测得全息存储时间衰减曲线.     

单斜辉石固溶体CaMgSi2O6-NaAlSi2O6的合成机理研究

 研究了压力和温度对单斜辉石的结晶和晶粒纤维编织的影响。在较低的晶化温度下压力对单斜辉石结晶的影响很明显，这种影响随温度升高而减弱。然而，压力对单斜辉石晶粒纤维编织的影响正相反，在相同的高温下，较高压力下晶化的单斜辉石晶粒纤维比较低压力下得到的晶粒纤维粗壮，而且编织紧密。     

Luminescence centers in Pb2Bi6O11 and Sn2Bi6O11 ceramics

We have studied the luminescence spectra and luminescence excitation spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics at 80 K. We have used the Alentsev-Fock to decompose the spectra into elementary components. We have established that the luminescence spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics contain three elementary bands each with maxima at 2.60, 2.32, 12.93 eV and 2.62, 2.30, 2.00 eV. Comparison of the data obtained with the results of a study of the luminescence spectra for a series of bismuth-containing oxide compounds suggest that luminescence of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ is due to radiative processes in structural complexes containing a bismuth ion in a nearest-neighbor oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 597–600, September–October, 2006.     

Optical spectroscopy of MgNb2O6 and ZnNb2O6 doped with Ni2+

Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 4, pp. 30–37, July–August, 1995.     

Domain structure in ferroelectric PbNb2O6

Single crystals of ferroelectric PbNb₂O₆ were grown employing a modification of the technique of Goodman. The results obtained on the domain structure were analysed and compared with those reported on BaTiO₃ and KNbO₃. The domain structure observed here corresponds to the twinning on (110) plane of the unit cell reported by Francombe and Lewis or the subcell reported by Labbe and others. The (001) planes were observed, as the crystal habit is such as to produce (001) planes, and the cleavage plane is also (001). Also the analysis of the observations can be done easily under these conditions. The domains observed are 90° domains with polar axis in (001) plane. Wedge shaped domains and spikes are present as in BaTiO₃ and KNbO₃. The twinning can occur also on plane producing a domain line at 90° with that due to twinning on (110). This gives patterns of perpendicular lines similar to those in KNbO₃ and BaTiO₃. Crystal structure considerations show that the domain structures with polarization in and out of the observed (001) plane are not possible, and also were not observed. In this sense, it is a two dimensional ferroelectric. The studies showed a peculiar grain structure in the crystals, and it can be explained on the basis of the growth habit of the crystal. The polarizing microscope is particularly useful in analysing the domain structure along with the grain structure.     

Temperature-dependent hyperfine parameters in CaFeSi2O6

Two samples of natural hedenbergite CaFeSi₂O₆ were studied in the temperature range from 4.2 K to 295 K, and at 78 K and 295 K in magnetic fields from 4.5 T to 7.5 T. The sign of V_ZZ is positive at 4.2 and 78 K and negative at 295 K. The asymmetry parameter depends strongly on the temperature. These results are explained by a simple model assuming a nondegenerated orbital doublet as ground state of Fe²⁺.     

Characteristics of thermoradiative destruction of BaS2O6·2H2O

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 613–618, October, 1991.     

Sodium pyroxene NaTiSi2O6: possible haldane spin-1 chain system

Using a density functional approach, we study the structural and magnetic properties of the pyrox-ene compound NaTiSi2O6. While all previous workers are taking that NaTiSi2O6 is a quasi-one-dimensional S=1/2 system, our theoretical results indicate that this is a Haldane S=1 chain compound below the phase transition at 210 K. A good agreement is obtained between the calculated and the measured Ti-Ti distances in the dimerized low temperature phase. We present a simple explanation of the flow of the unusual phase transition which is taking place in this compound.     

Optimizing conditions of fabrication and the properties of BaNb2O6-SrNb2O6 binary ceramics

Conditions for fabricating (Ba_0.5Sr_0.5)Nb₂O₆ ceramics are optimized. It is shown that materials synthesized at T = 1250°C and sintered at T = 1375–21400°C exhibit the best ceramic characteristics. The (Ba_0.5Sr_0.5)Nb₂O₆ solid solution is found to be a ferroelectric with a diffuse phase transition. The possibility of fabricating Ba_0.5Sr_0.5Nb₂O₆ thin films from ceramic targets prepared in the resulting optimum regimes is shown.     

Properties of clinopyroxene LiFeGe2O6

The polycrystalline compound LiFeGe₂O₆ has been synthesized by the solid-phase reaction. The X-ray diffraction, Mössbauer, calorimetric, and magnetic investigations have been carried out. The Mössbauer spectrum at 300 K represents a single quadrupole doublet. The isomer shift with respect to the metal iron α-Fe is 0.40 mm/s, which is characteristic of the Fe³⁺ high-spin ion in the octahedral coordination. The quadrupole splitting of 0.42 mm/s indicates a distortion of the oxygen octahedron around the iron cation. The results of the measurement of the temperature dependence of the heat capacity in the range 2–300 K have shown the presence of the only anomaly with a maximum at T _m ～ 20.5 K, which indicates the occurrence of a magnetic phase transition in this point. The data of the measurement of the temperature dependence of the magnetization have confirmed that the magnetic order with the dominant antiferromagnetic interaction of magnetically active ions exists in LiFeGe₂O₆ at a temperature below 20.5 K. The investigation of the temperature dependence of the heat capacity in the magnetic field H up to 9 T has demonstrated that the external factor insignificantly changes the order-disorder transition point (at H = 9 T, there occurs a shift of ～0.5 K toward the low-temperature range).

     

Diagonal antiferromagnetic easy axis in lightly hole doped Y1-xCaxBa2Cu3O6

Hole induced changes in the antiferromagnetic structure of a lightly Ca doped Gd:Y(1-x)CaxBa2Cu3O6 copper oxide single crystal with x approximately 0.008 is investigated by Gd3+ electron spin resonance. Holes do not localize to Ca2+ ions above 2.5 K since the charge distribution and spin susceptibility next to the Ca2+ are independent of temperature. Both hole doped and pristine crystals are magnetically twinned with an external magnetic field dependent antiferromagnetic domain structure. Unlike the undoped crystal, where the easy magnetic axis is along [100] at all temperatures, the easy direction in the hole doped crystal is along the [110] diagonal at low temperatures and changes gradually to the [100] direction between 10 and 100 K. The transition is tentatively attributed to a magnetic anisotropy introduced by hole ordering.     

Ionic conductivity of mixed K(NbW)O6 and KH2O(NbW)O6

The mixed oxides K(NbW)O₆ and KH₂O(NbW)O₆ were prepared by solid state reactions and characterized by X-Ray diffraction powder method, thermogravimetric analysis and differential scanning calorimetry. Electrical conductivity measurements were recorded between 190 and 508 K by the complex impedance method.     

Structure and proton mobility in the defect pyrochlore (H2O)xH2Ta2O6

The structure of the defect pyrochlore (D₂O)_0.38D₂Ta₂O₆ has been determined by powder neutron diffraction. The deuteroxyl deuterons randomly occupy sites ∼ 1.04 Å from the framework oxygens. The water molecules are situated on sites at the centre of the defect pyrochlore cavity, 8b position of Fd3m, and the O_W-D_W bonds lengths are 0.97 Å. A pulsed solid state N.M.R. study of (H₂O)_0.42H₂Ta₂O₆ has shown that this material is a reasonable proton conductor with a room temperature diffusion co-efficient of ∼ 10^-9 cm² s^-1.     

Electrical and Thermal Transport Properties of n-type Bi6Cu2Se4O6 (2BiCuSeO + 2Bi2O2Se)

New thermoelectric materials, n-type Bi₆Cu₂Se₄O₆ oxyselenides, composed of well-known BiCuSeO and Bi₂O₂Se oxyselenides, are synthesized with a simple solid-state reaction. Electrical transport properties, microstructures, and elastic properties are investigated with an emphasis on thermal transport properties. Similar to Bi₂O₂Se, it is found that the halogen-doped Bi₆Cu₂Se₄O₆ possesses n-type conducting transports, which can be improved via Br/Cl doping. Compared with BiCuSeO and Bi₂O₂Se, an extremely low thermal conductivity can be observed in Bi₆Cu₂Se₄O₆. To reveal the origin of low thermal conductivity, elastic properties, sound velocity, Grüneisen parameter, and Debye temperature are evaluated. Importantly, the calculated phonon mean free path of Bi₆Cu₂Se₄O₆ is comparable to the interlayer distance for BiO─CuSe and BiO─Se layers, which is ascribed to the strong interlayer phonon scattering. Contributing from the outstanding low thermal conductivity and improved electrical transport properties, the maximum ZT ≈0.15 at 823 K and ≈0.11 at 873K are realized in n-type Bi₆Cu₂Se_3.2Br_0.8O₆ and Bi₆Cu₂Se_3.6Cl_0.4O₆, respectively, indicating the promising thermoelectric performance in n-type Bi₆Cu₂Se₄O₆ oxyselenides.     

Nature of magnetism in Ca3Co2O6

We find using local spin density approximation + Hubbard U band structure calculations that the novel one-dimensional cobaltate Ca3Co2O6 is not a ferromagnetic half-metal but a Mott insulator. Both the octahedral and the trigonal Co ions are formally trivalent, with the octahedral being in the low-spin and the trigonal in the high-spin state. The inclusion of the spin-orbit coupling leads to the occupation of the minority-spin d2 orbital for the unusually coordinated trigonal Co, producing a giant orbital moment (1.57 microB). It also results in an anomalously large magnetocrystalline anisotropy (of order 70 meV), elucidating why the magnetism is highly Ising-like. The role of the oxygen holes, carrying an induced magnetic moment of 0.13 microB per oxygen, for the exchange interactions is discussed.     

Topological phase transition in the trirutile-type MgBi2O6

Based on the first-principle calculations and k⋅p effective model analysis, we predicted a new topological semimetal (TSM) MgBi₂O₆. Without spin-orbit-coupling (SOC) and under the generalized-gradient-approximation (GGA), MgBi₂O₆ is a nodal-line semimetal. When the exchange-correlation energy was changed to HSE06, MgBi₂O₆ was trivial insulator in the equilibrium volume, but it became TSM under 7% hydrostatic tensile strain. MgBi₂O₆ might be an important platform to study the topological properties because of the two following advantages for measurements: (1) The nodal line, drumhead-liked surface state and Fermi Arc are very closely to the Fermi level; (2) The band structure is very “clean” (no other bulk bands except the related inverted conduction and valence bands around the Fermi level), which avoids the surface states been embedded into the bulk states.     

Observation of multiferroic properties in pyroxene NaFeGe2O6

We report the observation of multiferroicity in a clinopyroxene NaFeGe(2)O(6) polycrystal from the investigation of its electrical and magnetic properties. Following the previously known first magnetic transition at T(N1) = 13 K, a second magnetic transition appears at T(N2) = 11.8 K in the temperature dependence of the magnetization. A ferroelectric polarization starts to develop clearly at T(N2) rather than T(N1) and its magnitude increases up to ~13 μC m(-2) at 5 K, supporting the idea that the ferroelectric state in NaFeGe(2)O(6) stems from a helical spin order stabilized below T(N2). When a magnetic field of 90 kOe is applied, the electric polarization decreases to 9 μC m(-2) and T(N2) slightly increases by 0.5 K. At intermediate magnetic fields, around 28 and 78 kOe, anomalies in the magnetoelectric current, magnetoelectric susceptibility, and field derivative of magnetization curves are found, indicating field-induced spin-state transitions. Based on these electrical and magnetic properties, we provide a detailed low temperature phase diagram up to 90 kOe, and discuss the nature of each phase of NaFeGe(2)O(6).