液相外延(BiTm)_3(FeGa)_5O_(12)石榴石单晶薄膜的X射线双晶衍射仪研究

本文用X射线双晶衍射仪和光学偏光显微镜对不同液相外延温度生长的(BiTm)(FeGa)_5O_(12)石榴石单晶薄膜进行了研究。发现随着生长温度的下降,薄膜的点阵常数增加,比法拉第旋转角θ_F增大。同时发现液相外延单晶石榴石薄膜是由点阵常数或取向略有差别的两层组成。当薄膜的晶格失配大于10~(-3)时薄膜将破裂。     

Li2K(IO3)3与Li2NH4(IO3)3的晶体结构

本文用X射线粉末法测定了Li₂K(IO₃)₃与Li₂NH₄(IO₃)₃的晶体结构和原子参数。发现Li₃K(IO₃)₃,Li₂NH₄(IO₃)₃与Li₂Rb(IO₃)₃同晶型,属单斜晶系,空间群为P2₁/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。 关键词：     

K5Bi(MoO4)4-Nd3+晶体生长和光学性质

在化学计量的熔料里,用提拉法生长了K₅Bi_0.9Nd_0.1(MoO₄)₄和K₅Bi_0.97Nd_0.03(MoO₄)₄单晶。该晶体属于三方晶系,空间群为R3m,Z=1.5,晶胞常数为a=6.023?,c=20.887?(Nd_0.1)。K₅Bi(Mo 关键词：     

LiIO3-Zn(IO3)2 赝二元系的研究

用固态粉末烧结法配制样品,用X射线衍射及差热分析等方法研究并测定了LiIO₃-Zn(IO₃)₂赝二元系的相图。该二元系内存在一新相LiZn(IO₃)₃。它有较大的倍频效应,具有离子导电性。用自编的由粉末衍射数据求单斜晶系的点阵参数的计算机程序成功地求出了该化合物的点阵常数。经过进一步修正,确定它属于正交晶系,α=8.08l?,b=8.729?,c=11.595?,z=4。并确定了化合物存在的成分范围和条件。 关键词：     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

R3(Fe,Mo)29Nx的晶体学特性和内禀磁性

研究了R₃(Fe,Mo)₂₉(R=Ce,Nd,Sm,Gd,Tb,Dy,Y)氮化物的晶体学特性和内禀磁性.主要研究内容为：氮化对R₃(Fe,Mo)₂₉金属间化合物的点阵参数、居里温度T_C、饱和磁化强度σ_s和各向异性场B_a的影响. 关键词：     

Pr0.7(Sr1-xCax)0.3MnO3多晶体系中的小极化子性质

采用基于柠檬酸体系的溶胶-凝胶法制备了Pr_0.7（Sr_1-xCa_x）_0.3MnO₃系列的多晶块材, 同时还用脉冲激光沉积技术（PLD）在SrTiO₃（100）衬底上外延生长了同一系列的薄膜, 系统研究了它们的晶格结构和电输运行为. 多晶和薄膜样品都具有正交晶格结构, 电输运行为在居里温度T_Ｃ以上的高温顺磁相都很好 关键词： 0.7（Sr_1-xCa_x）_0.3MnO₃')" href="#">Pr_0.7（Sr_1-xCa_x）_0.3MnO₃ 绝热小极化子模型 双交换作用 Jahn-Teller晶格畸变     

Fe(NH2trz)3·(BF4)2掺杂聚芴的有机电致发光器件

对于RGB有机电致发光器件(OLEDs),蓝光非常重要.在现有各种蓝光材料中,聚芴(PFO)非常稳定且荧光量子效率可达80%,但它有一个非常大的缺点:电致发光会产生异常绿光带.这严重影响了PFO相关器件的饱和色纯度.本文使用分子基磁性材料Fe(NH₂trz)₃·(BF₄)₂掺杂PFO方法,解决了这一难题.以ITO为衬底,制作了结构为ITO/PEDOT:PSS/PFO:Fe(NH₂trz)₃·(BF₄)₂/CsCl/Al的器件.报道了利用Fe(NH₂trz)₃·(BF₄)₂特殊的电子自旋态调制PFO的光电特性,实现了PFO的强烈纯正蓝光发射.详细研究了Fe(NH₂trz)₃·(BF₄)₂对PFO光电特性的影响.在4 V至9 V电压的偏置下,没有Fe(NH₂trz)₃·(BF₄)₂的器件,发出特别异常的绿光.然而,与此形成明显对照的是:Fe(NH₂trz)₃·(BF₄)₂掺杂的器件发出强烈的本征蓝光;PFO绿色发光带被成功压制;随着电压的变化,器件光谱的蓝光部分在整个EL谱所占比例没有改变.运用光电磁一体化测量技术,进一步研究了PFO掺杂Fe(NH₂trz)₃·(BF₄)₂器件的磁发光(MEL)和磁电导(MC)效应.发现PFO:Fe(NH₂trz)₃·(BF₄)₂和纯PFO薄膜内都没有激基缔合物产生.运用发光动力学理论,分析了Fe(NH₂trz)₃·(BF₄)₂阻断PFO异常绿光发射的机理.     

氧压对Ba0.6Sr0.4TiO3薄膜晶格常数的影响及BaTiO3/Ba0.6Sr0.4TiO3超晶格的制备

采用脉冲激光沉积(PLD)技术,经一系列的优化实验成功地制备了BaTiO₃(BT)和Ba_0.6Sr_0.4TiO₃(BST)单层膜.X射线衍射分析表明,在LaAlO₃(001)单晶平衬底上生长的BT和BST薄膜都是沿[001]取向的近外延生长.且随着氧压在10^-3—25 Pa范围内逐渐增大,BST薄膜的晶格常数与氧压之间近似满足Boltzmann函数关系.其次,在此优化条件下还 关键词： 超晶格 晶格常数 激光感生热电电压 脉冲激光沉积     

Pb(Zr0.3Ti0.7)O3铁电薄膜激光感生电压效应

采用脉冲激光沉积(PLD)技术在LaSrAlTaO₃(LSATO),LaAlO₃(LAO)和SrTiO₃(STO)的单晶倾斜衬底上成功制备了Pb(Zr_0.3Ti_0.7)O₃(PZT)薄膜,在三种倾斜衬底上生长的PZT薄膜中都首次发现了LIV效应.对PZT/LSATO薄膜在a,c轴两种不同取向择优生长下的LIV效应做了研究,发现在薄膜c轴取向择优生长 关键词： 激光感生电压效应 铁电薄膜 薄膜生长取向 原子层热电堆     

晶格失配应力对单晶(BiTm)_3(GaFe)_5O_(12)膜磁畴结构的影响

利用液相外延工艺在钆镓石榴石衬底上制得了单晶(BiTm)_3(GaFe)_5O_(12)膜,研究了晶格失配应力对其磁畴结构的影响.研究发现,生长速率越快,膜的晶格常数越大;晶格失配应力可以在一定范围内调整膜的垂直各向异性;随着晶格失配应力由较大张应力逐渐转变为较大压应力,磁畴形状先由磁泡畴转变成迷宫畴,然后转变为过渡态部分弯曲的条状畴,最终转变为整齐排列的条状畴;失配应力同时对畴宽也有影响,膜受到的失配应力越大,畴宽越大.这一实验研究对基于控制晶格失配应力来调控单晶膜的各向异性和磁畴结构有指导意义.     

Factors affecting coercivity in (Y,Sm,Tm)3(FeGa)5O12 and (Y,Sm,Lu,Ca)3(FeGe)5O12 LPE films

Factors which influence coercivity, H_c, in (Y,Sm,Lu,Ca)₃(FeGe)₅O₁₂ films and in (Y,Sm,Tm)₃(FeGa)₅O₁₂ films grown by LPE have been identified. An anomalous layer at the film-substrate interface exhibits coercivity values different from that of the middle, bulk, portion of the film. The contribution of the transient layer at the substrate interface could be reduced by increasing the rotation rate while immersing the substrate into the melt. Films containing Ga show lower coercivities than films containing CaGe possibly because films with Ga are more uniform in composition. Films with Ga show increased coercivities with increasing growth rates and with increasing Sm content throughout the film.     

The crystal structures of the ion conductors (NH+4)Zr2(PO4)3and (H3O+)Zr2(PO4)3

The crystal structures of (NH⁺₄)Zr₂(PO₄)₃ and (H₃O⁺)Zr₂(PO₄)₃ have been determined from neutron time-of-flight powder diffraction data obtained at 15 K. Both compounds are rhombohedral, $\text{R}\text{3}\text{c}$, with cell parameters a=8.7088(1) and c=24.2197(4) Å for the ammonium compound and a=8.7528(2), c=23.6833(11) Å for the hydronium compound. In both cases the ions are completely localized in the type I cavities and hydrogen bonded to lattice oxygens. The measured unit cell parameters are relatively large for this class of compounds but the entrance ways into the cavities are still too small to allow for unrestricted movement of the ions. Thus the low conductivity of the hydronium ion is related to this and other structural features.     

Crystallographic study of the phase transition in (Me4P)2ZnBr4

The compound (Me₄P)₂ZnBr₄, a member of the β-K₂SO₄ structure class, undergoes a phase transition at 84°C from the room temperature space group P12₁/c1 to the parent Pmcn structure. The room temperature structure corresponds to a ferrodistortive transition of B_1g symmetry at the zone center. At room temperature, the compound has lattice constants a=9.501(1), b=16.055(2), c=13.127(2) Å and β=90.43(1)°. For the high temperature phase, the orthorhombic cell has dimensions a=9.466(2), b=16.351(3) and c=13.284(2) Å. The structures consist of two crystallographically independent Me₄P⁺ cations and the ZnBr₄²⁻ anions. In the room temperature phase, all three ionic species show substantial displacement from the mirror plane perpendicular to the a-axis that exists in the high temperature phase, as well as rotations out of that plane. The thermal parameters of the cations are indicative of substantial librational motion. Measurements of lattice parameters have been made at 2-5°C intervals over the temperature range 40-140°C. The changes in the lattice constants appear continuous at T_c (within experimental limits) indicating that the phase transition is likely second-order. The a lattice constant shows an anomalous shortening as T_c is approached. Thermal expansion coefficients are calculated from this data. An application of Landau theory is used to derive the temperature dependencies of spontaneous shear strain and corresponding elastic stiffness constants associated with the primary order parameter.     

Coercivity mechanism of Sm(Co, Cu)5

The mechanism of the high intrinsic coercivity of the Sm(Co_1−xCu_x)₅ (0≦x<1) system was studied by relating the coherency between the lattice constants of hexagonal Sm(Co, Cu)₅ and hcp Co to the coercive force. It was found analytically that the intrinsic coercive force reaches a maximum in the composition range from x=0.6 to 0.8, where the lattice mismatch approaches zero, so that there is a strong correlation between lattice matching and coercive force. When a Sm ion was located within a Sm(Co, Cu)₅ grain and in the outmost edge of the a and c planes of its grain surrounded or not surrounded by the coherent Co phase, the crystal field parameter at each Sm³⁺ site was calculated using a point charge model under the assumption that the Co and Cu atoms located in a grain and the hcp Co atoms situated at the interface uniformly have a charge of 3/5−. The results indicated that the Co phase precipitated coherently along the grain boundaries effectively enhances the magnetocrystalline anisotropy of Sm ions located in the outmost edges of the a and c planes of a Sm(Co, Cu)₅ grain.     

On the power-law behavior of the AC conductivity of the mixed crystal (NH4)3H(SO4)1.42(SeO4)0.58

A power law used to describe the AC conductivity from 299 to 393 K of the mixed crystal (NH₄)₃H(SO₄)_1.42(SeO₄)_0.58 led to fractional exponent values ranging from 1.08 to 0.91, depending on structural changes induced on temperature variation [B. Louati, M. Gargouri, K. Guidara and T. Mhiri, J. Phys. Chem. Solids 66 (2005) 762]. In the present note, we suggest that the fractional law exhibits features of lattice relaxation. Despite the structural changes, the parameters of the power law are mutually interconnected to yield a temperature independent phenomenon. Such behavior is probably of general validity and characterizes the universal fractional dispersion of the AC conductivity, as it was also observed in glasses of different composition.     

Growth and spectroscopic properties of Yb-doped Li6Y(BO3)3 single crystal

The spectroscopic properties of high-quality Czochralski grown 20% Yb³⁺-doped Li₆Y(BO₃)₃ single crystal as new promising laser material are presented. The crystal was seeded-grown in the 〈0 1 0〉 direction and its crystallinity was measured using X-ray rocking curve analysis. Low temperature transmission spectrum exhibits broad bands in a short range of wavelengths and two sharp lines at 972.5 and 978 nm, interpreted as two zero-lines of two nonequivalent Yb³⁺ centers inside the lattice. The fluorescence lifetimes associated to these two intense lines are different: 0.867 and 1.33 ms. An attempt of determination of the Stark sublevels energies of the ⁴F_5/2 and ⁴F_7/2 manifolds of the two Yb³⁺ nonequivalent ions is given. The polarized absorption and emission spectra were also recorded at room temperature and we conclude that the most favorable emission line for laser application could be around 1042 nm in n_g polarization.     

Lattice parameters variation with temperature of Ti2O3 and (Ti0.98V0.02)2O3 from single crystal X-ray data

The lattice parameters of Ti₂O₃ and (Ti_0.98V_0.02)₂O₃ have been measured as a function of temperature (24–670°C for Ti₂O₃ and 24–440°C for V-doped Ti₂O₃) from single crystal X-ray data. The high temperatures were attained by blowing hot argon directly on the crystal mounted on an automatic Philips diffractometer. This experimental set-up gives standard deviations which are at least 10 times better than those of the previous measurements and allows to keep Ti₂O₃ as such well above the transition. The variations of a, c, $\text{c}\text{a}$ (hexagonal axes) for pure Ti₂O₃ are in agreement with the previous results. On the contrary we did not observe any transition in the unit cell volume. The V-doping seems to attenuate the transition which is visible only on the a vs T curve     

Spectroscopic properties of Yb ions in La2(WO4)3 crystal

Yb³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. Absorption and fluorescence spectra of the crystal were recorded at the room temperature. The stimulated emission cross-sections of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg formula, respectively. The fluorescence decay curves of ²F_5/2 manifold of Yb³⁺ ions were recorded at room temperature for both crystal and powder samples. The effect of radiation trapping on the spectroscopic properties is discussed. Comparison with other Yb³⁺-doped laser crystals is made. The results show that Yb³⁺:La₂(WO₄)₃ crystal is a promising laser material.