Magnetization anomaly and anisotropy of Bi2Sr2CaCu2−xNixO8 single crystals

We have observed the anomalous magnetization of Bi₂Sr₂CaCu_2−xNi_xO₈ (x = 0 and 0.02) single crystals. Anisotropy decreases with iodine intercalation although it expands the space between CuO₂ layers. Iodine intercalation seems to suppress the magnetization anomaly for Ni = 1% crystals, but not for Ni = 1% substituted crystals. We have discussed these results in terms of the increase of anisotropy by Ni substitution and the dimensional crossover of flux lines. Effects of both oxygen concentration and substitution of a magnetic element for the Cu site on the anisotropy of Bi₂Sr₂CaCu₂O₈ crystals show the same tendency as the case of the YBa₂Cu₃O₇ superconductor.     

Bi-Sr-Ca-Cu-O2212相超导单晶的定向生长

用定向凝固法已成功地生长出Bi-Sr-Ca-O2212相的超导大单晶,最大的单晶尺寸达到19×3×2mm³。定向生长的单晶(001)面平行于生长方向,[100]方向为单晶的定向生长方向。劳厄像表明大晶体确为单晶,其质量比其它方法生长的单晶要高。氧气中退火后的单晶电阻测量和交流磁化率测量表明,零电阻温度T_c(0)=81.5k。 关键词：     

Thin film bilayers of multiferroic bismuth ferrite on Pt–Si substrate

A multiferroics/multiferroics BiFeO₃/Bi_0.90La_0.10Fe_0.90Zn_0.10O₃ (BFO/BLFZO) bilayer was deposited on Pt/TiO₂/SiO₂/Si substrates by radio frequency sputtering. The BLFZO layer strongly affects the phase purity, orientation growth, and leakage current of BFO layer. The bilayered capacitor exhibits a high dielectric permittivity of ～162 and an improved magnetic behavior of 2M_s ～ 34.6 emu/cm³, together with an excellent fatigue endurance. A remanent polarization of 2P_r ～ 116.2 μC/cm² for the bilayered capacitor is better than those of reported BFO bilayers. The impedance study indicates that lower freely mobile charges are responsible for the improved electrical behavior of the BFO/BLFZO bilayer. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and NO_2-gas sensing property of individual β-Ga_2O_3 nanobelt

Monoclinic gallium oxide (β-Ga_2O_3) nanobelts are synthesized from gallium and oxygen by thermal evaporation in an argon atmosphere and their NO_2 sensing properties are studied at room temperature.Electron microscopy studies show that the nanobelts have breadths ranging from 30 to 50 nm and lengths up to tens of micrometers.Both the x-ray diffraction (XRD) and the selected are electron diffraction (SAED) examinations indicate that β-Ga_2O_3 nanobelts have grown into single crystals.Room temperature NO_2 sensing tests show that the current of individual β-Ga_2O_3 nanobelt decreases quickly,and then gently when the NO_2 concentration increases from low to high.It is caused by the NO_2 molecule chemisorption and desorption processes in the surface of β-Ga_2O_3 nanobelt.     

The growth of a single crystal of Sr3CuIrO6 and its magnetic behavior compared to polycrystals

We have grown single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. We present the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline form reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (T ₁) and 19 K (T ₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.     

Fabrication of NdBa2Cu3O7−δ single crystals by the top-seeded solution-growth method in 1%, 21%, and 100% oxygen partial pressure atmosphere

Single crystals of NdBa₂Cu₃O_7−δ (Nd123) have been successfully grown by the top-seeded solution-growth (TSSG) method in 1%, 21% and 100% oxygen partial pressure atmosphere ((P(O₂) = 0.01 atm, P(O)₂) = 0.21 atm and P(O₂) = 1.00 atm). Ba---Cu---O solvent with a Ba to Cu ratio of 3:5 was used in a Nd₂O₃ crucible. Nd is supplied by the reaction between the molten solvent and the Nd₂O₃ crucible. Compositions of Nd123 single crystals grown in different oxygen partial pressure atmospheres were analyzed by inductivity coupled plasma atomic emission spectrometry (ICP-AES) and confirmed to be Nd:Ba:Cu = 1.01:1.97:3.00 for P(O₂) = 0.01 atm, Nd:Ba:Cu = 1.07:1.95:3.00 for P(O₂) = 0.21 atm and Nd:Ba:Cu = 1.10:1.90:3.00 for P(O₂) = 1.00 atm, respectively. The Nd123 single crystals grown in different oxygen partial pressure atmospheres were annealed in a pure oxygen gas flow, and the temperature dependence of the DC magnetization for these crystals was measured using a superconducting quantum interference device (SQUID) magnetometer. The Nd123 single crystal grown in P(O₂) = 0.01 atm, and annealed at 340°C for 200 h showed a steep superconductive transition at 96 K. On the other hand, the Nd123 crystal grown in P(O₂) = 0.21, 1.00 atm and, annealed at 340°C for 200 h exhibited a broad transition at 92 K for P(O₂) = 0.21 atm and at 88 K for P(O₂) = 1.00 atm, respectively. Therefore for Nd123 single crystal production with high quality superconductive characteristics, a low oxygen partial pressure atmosphere during crystal growth is found to be effective for minimizing the substitution of Nd ions into Ba sites.     

强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

NaREO2 (RE= Lu，Y) 的制备及其结构的研究

用高温固相法制备了NaLuO2和NaYO2晶体粉体.制备纯相的NaLuO2粉体晶体困难,而制备纯相NaYO2粉体晶体相对容易.为了测定NaLuO2产物中含少量Lu2O3不纯相的量,用X射线衍射绝标法确定了样品中这两者的重量比和谱峰比的关系,得到了绝标法常数kLu2O3关键词： 2')" href="#">NaLuO2 2')" href="#">NaYO2 2O3')" href="#">Lu2O3 XRD定量分析 稀土发光     

Hydrogen-deuterium exchange induced by an electric field in α-Al2O3 single crystals

Abstract

Hydrogen and deuterium are observed in α-Al₂O₃ crystals in the form of OH^? and OD^? radicals, respectively, which absorb in the infrared region. Infrared-absorption measurements were used to monitor diffusion of deuterons and protons in α-Al₂O₃ single crystals under the application of a moderate electric field parallel to the crystallographic c-axis, in the temperature range of 973—1333K. A linear dependence of the percent of exchange with both annealing time and applied voltage is observed, indicating that ionic conduction was taking place. The activation energy for the H⁺  D⁺ exchange was determined to be 2.4 eV, less than half the value obtained by pure thermal means, suggesting that under the application of an electric field the deuteron (proton) diffusion mechanism is different.     

Unique crystal growth with crystal axis rotation in multi-ferroic β′-(Sm,Gd)2(MoO4)3 narrow lines patterned by lasers in glass

The morphology and orientation of multi-ferroic β′-(Sm,Gd)₂(MoO₄)₃ crystals in the lines patterned by laser irradiations in 3Sm₂O₃–18.25Gd₂O₃–63.75MoO₃–15B₂O₃ (mol%) glass were examined using transmission electron microscope (TEM) observations in order to clarify the origin of the appearance of periodic birefringence in an atomic-scale level. The crystallographic direction of crystals in the lines was determined from selected area electron diffraction (SAED) patterns in TEM observations, and it was demonstrated that a gradual rotation of crystallographic axes takes place along the crystal growth direction (laser scanning direction). The unique crystal growth with a spiral-like rotation of the crystallographic axes is due to the gradual rotation of (MoO₄)²⁻ tetrahedral units in β′-(Sm,Gd)₂(MoO₄)₃ crystals. The laser-induced crystallization, in which the region and direction of crystal growth are restricted artificially to a narrow space, provides a new crystal growth engineering.     

(Ba, Ca)(Ti, Zr)O3-BiFeO3 lead-free piezoelectric ceramics

Effects of BiFeO₃ (BFO) content on the microstructure and electrical properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCTZ) ceramics prepared by normal sintering in air were investigated. A stable solid solution is formed between BCTZ and BFO. The grain size gradually becomes smaller, and the ceramics become denser with increasing the BFO content. The Curie temperature, dielectric constant, and dielectric loss of BCTZ ceramics decrease simultaneously with the introduction of BFO. Moreover, the remanent polarization reaches a maximum at x = 0.2 mol%, and the coercive field continuously increases with increasing the BFO content due to the introduction of BFO with a higher coercive field. Improved piezoelectric properties (d₃₃ ∼ 405 pC/N and k_p ∼ 0.44) are demonstrated for the BCTZ ceramic with x = 0.2 mol%.     

Preparation and characterization of Y1−xPrxBa2Cu3O7−δ single crystals

We present a reliable method for growing single crystals of Y_1−xPr_xBa₂Cu₃O_7−δ high-T_c superconductors in ZrO₂ crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al₂O₃ crucibles. We describe techniques for crystal growth in both Al₂O₃ and ZrO₂ crucibles using an excess of BaCo₃ and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant.     

复合薄膜NiFe2 O4-BiFeO3 中的磁电耦合

采用化学溶液沉积法(CSD)在Au/Ti/SiO₂/Si衬底上通过自组装生长制备了BiFeO₃-NiFe₂O₄ (BFO-NFO)多铁性复合薄膜.X射线衍射图谱(XRD)显示形成了分离的钙钛矿结构的铁电相BFO和尖晶石结构的铁磁相NFO. NFO的引入导致复合薄膜的泄漏电流减小,剩余极化强度增加.相比于纯BFO薄膜,0.25NFO-0.75BFO样品泄漏电流下降了约两个数量级,剩余极化强度( M _{关键词： 多铁性复合薄膜 磁电耦合 铁电性 铁磁性}     

Radiation-Induced Paramagnetic Centers in the Glasses Of CaO-Ga2O3-GeO2 System

The X-band (v ? 9.4 GHz) ESR spectra of the UV-, X-, and γ-irradiated glasses of CaO-Ga₂O₃-GeO₂ system with compositions similar to Ca₃Ga₂Ge₃O₁₂, Ca₃Ga₂Ge₄O₁₄, and Ca₃Ga₂O₆ crystals have been investigated at 300 and 77 K. It was shown that X- and γ-irradiation of the Ge-contained glasses induce simultaneously electron and hole paramagnetic centers, stable at room temperature. The UV-irradiation of Ge-contained glasses leads to the generation of stable centers of electron type, whereas the X- and γ-irradiation of glasses with Ca₃Ga₂O₆ composition induces stable hole centers, exclusively. The electron centers are assigned to E′ (Ge) centers with different local environments. ESR spectrum of hole centers is ascribed to O^? centers, localized on non-bridging oxygen of the glass network. The E′ (Ge) and O^? centers show high thermal stability in the CaO-Ga₂O₃-GeO₂ glass network. The obtained ESR spectra are described by spin Hamiltonian with g-factor of axial and rhombic symmetry for the E′ (Ge) and O^? centers, respectively. The nature, electron structure and some formation peculiarities of the radiation defects in CaO-Ga₂O₃-GeO₂ glasses are discussed in comparison with other glasses as well as Ca₃Ga₂Ge₃O₁₂ and Ca₃Ga₂Ge₄O₁₄ crystals.     

Influence of nanocrystalline phases on the electrical properties of lithium titanate phosphate glass ceramics mixed with Ga2O3 nanocrystals

Several glass ceramic compositions dispersed with Ga₂O₃ nanocrystals, in the series samples (100???x)[0.4Li₂O–0.1TiO₂–0.5P₂O₅]?+?xGa₂O₃ with x?=?0, 2, 4, 6, 8, and 10?mol% of Ga₂O₃ were synthesized via high-energy ball milling technique and labeled as lithium gallium titanate phosphate glass (LTPG _x ) (x is the mol% of Ga₂O₃ nanocrystals). The compositions have been selected on the basis of thermal stability data obtained from differential thermal analysis. X-ray diffraction studies indicate nanocrystalline phase formation in the controlled crystallized glasses. The variation of electrical conductivity was explained in the light of growth of nanocrystalline phases. The best bulk conductivity (σ?=?7.03?×?10^?4?S?cm^?1, at 303?K) was achieved by the sample containing 8?mol% of Ga₂O₃ nanocrystals content, labeled as LTPG₈ sample. The activation energy for conduction (E_{a σ} ) is obtained from the temperature dependent of conductivity data, which is fitted to Arrhenius equation. The single super curve in the scaling spectra suggested the temperature-independent relaxation phenomenon.     

Surface morphology of PrBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> single crystals after the long-lasting high-temperature reduction

The results of the detailed scanning electron microscopy study of PrBa₂Cu₃O_7-δ single crystals after the long-lasting high-temperature post-growth treatment are reported. The presence of the unstable decomposition products on the crystal surface indicates that the onset of superconductivity must be related to the structural transformations in the bulk (approximately 20% of the total volume of the examined crystals). The time-dependent character of the superconductivity in the Pr-123 crystals could be attributed to the migration of defects in the Pr−Ba sublattice from the bulk toward the surface.     

Lithium ion conductive glass–ceramics with Li3Fe2(PO4)3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li₂O–(25 − x)Fe₂O₃–xNb₂O₅–37.5P₂O₅ (mol%) (x = 5,10,15) are prepared, and it is found that the addition of Nb₂O₅ is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li₃Fe₂(PO₄)₃ crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10^− 6 Scm^− 1 at room temperature and the activation energies of 0.48 eV (x = 5) and 0.51 eV (x = 10) for Li⁺ ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li₃Fe₂(PO₄)₃ crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li₃Fe₂(PO₄)₃ crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.     

High magnetic field properties of mixed terbium-yttrium ferrite garnets

Magnetization measurements in d.c. magnetic fields up to 180 kOe have been performed on polycrystalline specimens and on single crystals of mixed terbium-yttrium iron garnets: Tb _x Y_3–x Fe₅O₁₂ in the 4.2–300 K temperature range. On polycrystals (x=2.5; 2; 1; 0.37) the concentration dependence of both compensation point and spontaneous magnetization has been determined. In the single crystals (x=2; 1; 0.37) a strong magnetic anisotropy has been observed with a change of the easy direction of magnetization from [111] to [100] whenx decreases; abrupt field-induced transitions have been observed at low temperatures when the external field is applied along the [100] direction.     

Growth and characterization of ferroelectric SrBi2Ta2O9 single crystals via high-temperature self-flux solution method

SrBi₂Ta₂O₉ (SBT) single crystals were produced by the high-temperature self-flux solution method using a Bi₂O₃ flux modified with B₂O₃. The processing conditions were optimized to obtain large and translucent SBT crystals with a layered habit and typical dimensions of approximately 7 × 5 × 0.2 mm. X-ray diffraction and x-ray topography measurements revealed that the major faces of the crystals with natural rectangular platelet morphology are perfectly (001)-oriented with edges directed along the [110] directions. The high quality of the crystals was confirmed by rocking curves (half-width of 0.04° for the (0018) reflection) and by ferroelectric measurements. The anisotropy in the dielectric and ferroelectric properties was investigated both along the [110] (ab plane) and the [001] (c axis) directions. The growth mechanism, morphology, and dielectric anisotropy of the SBT crystal platelets are discussed based on its crystallographic structure. This article was submitted by the authors in English     

Synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al₂O₃ substrate, ZnAl₂O₄/α-Al₂O₃ complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl₂O₄ changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl₂O₄ transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present that ZnAl₂O₄ prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl₂O₄/α-Al₂O₃ substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl₂O₄ layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl₂O₄ layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film.