Gd5Si2Ge2相的线状缺陷

使用X射线粉末衍射(XRD)表征了电弧炉熔炼的Gd5Si2Ge2.2合金的相组成,结果表明Gd5Si2Ge2.2合金主要由Gd5Si2Ge2相和GdGe相构成。扫描电镜(SEM)分析表明,Gd5Si2Ge2晶粒内部有大量规则分布的线状特征;透射电镜(TEM)研究发现了Gd5Si2Ge2相的基体上存在两种不同形态的线条组织,选区电子衍射证明两种不同形态的线条组织既非第二相也非孪晶;根据高温原位金相观察的结果推测,该线状组织是在液-固相变过程中形成的。     

稀土Gd5Ge2(Si2-xAlx)合金系的晶体结构和磁卡效应研究

用磁控电弧炉在氩气气氛下熔炼了Gd5Ge2(Si2-xAlx) (x=0, 0.1, 0.2, 0.5, 1.0)系样品.X射线粉末衍射分析表明, 样品基本为单相结构, 其晶体对称性不会随Al含量的增加而改变.用振动样品磁强计测量了样品的M-T曲线和不同温度下的M-H曲线.居里温度随Al含量x的增加略有减小, 当 x=0.2时Gd5Ge2(Si2-xAlx)有最大-ΔSM值.退火对样品的居里温度和磁卡效应影响不大, 退火前后的居里温度和磁卡效应基本保持一致.     

Electron-deficient Eu(6.5)Gd(0.5)Ge6 intermetallic: a layered intergrowth phase of the Gd5Si4- and FeB-type structures

A novel electron-poor Eu(6.5)Gd(0.5)Ge? compound adopts the Ca?Sn?-type structure (space group Pnma, Z = 4, a = 7.5943(5) ?, b = 22.905(1) ?, c = 8.3610(4) ?, and V = 1454.4(1) ?3). The compound can be seen as an intergrowth of the Gd?Si?-type (Pnma) R?Ge? (R = rare earth) and FeB-type (Pnma) RGe compounds. The phase analysis suggests that the Eu(7-x)Gd(x)Ge? series displays a narrow homogneity range of stabilizing the Ca?Sn? structure at x ≈ 0.5. The structural results illustrate the structural rigidity of the 2(∝)[R?X?] slabs (X = p-element) and a possibility for discovering new intermetallics by combining the 2(∝)[R?X?] slabs with other symmetry-approximate building blocks. Electronic structure analysis suggests that the stability and composition of Eu(6.5)Gd(0.5)Ge? represents a compromise between the valence electron concentration, bonding, and existence of the neighboring EuGe and (Eu,Gd)?Ge? phases.     

Gd5Si1.75Ge1.75Sn0.5的结构、磁相变与磁熵变

采用粉末XRD和振动样品磁强计研究了Gd5Si1.75Ge1.75Sn0.5合金的结构、磁相变和低场变化下的磁熵变。磁性测量结果表明,Gd5Si1.75Ge1.75Sn0.5合金的磁化强度在居里温度附近发生突变,具有一级相变的典型特征,室温具有Gd5Si2Ge2型单斜结构;合金低场磁热效应非常明显,1.8T磁场变化下,在其居里温度272K附近的最大磁熵变为16.7J.kg-1.K-1。用成本低廉的Sn取代Gd5Si2Ge2中部分Si和Ge后,Gd5Si1.75Ge1.75Sn0.5在低磁场变化下的磁熵变比金属Gd大得多并略高于Gd5Si2Ge2。     

Amorphous-to-crystalline transition in Te-doped Ge2Sb2Se5 glass

Differential scanning calorimetry (DSC) was used to study crystallization in Ge₂Sb₂Se_4.5Te_0.5 glass under non-isothermal conditions. The crystallization kinetics was described in terms of the autocatalytic ?esták–Berggren model. An extensive discussion of all aspects of a full-scale kinetic study for a crystallization process was undertaken. In particular, the effect of Te ? Se substitution on the complexity of the crystallization process was analyzed. The addition of tellurium enhances bulk crystallization originating from volume nuclei at the expense of the surface/defects-based crystallization mechanism. Significantly higher activation energy in the case of the Te-doped material was attributed to the larger mass of the combined Se–Te chains and the larger spatial restrictions for their movement. On the other hand, the slightly lower crystallization temperature of the Te-doped glass corresponds to its higher tendency for crystallization. A supplemental X-ray diffraction study confirmed the findings obtained by DSC.     

Structural phase transition of Gd3RuO7

Structural phase transition of trigadorinium ruthenium heptaoxide, Gd(3)RuO(7), has been investigated by in situ high-temperature single-crystal X-ray diffraction. A small shrinkage in b-length and an expansion in c-length were observed between 363 and 383 K with increasing temperature. No significant change occurred in a-length within experimental errors. The changes were essentially reversible against temperature. Structures of the high-temperature modification have been determined at 423, 773, and 1223 K assuming the orthorhombic Cmcm symmetry. The structure of the low-temperature modification has been determined at 293 K, assuming the orthorhombic P2(1)nb symmetry with doubled unit cell along the b-axis of the high-temperature modification. The transition from high- to low-temperature modification can be structurally characterized by tilts about axes close to the c-axis of the unit cell occurring on half of the RuO(6) octahedra. These octahedral tilts couple with a reduction in coordination number of the Gd atom bridging the adjacent RuO(6) single chains along the b-axis. The present study also revealed the presence of structural disorder in the high-temperature Cmcm modification that had not been reported for the archetypal Cmcm structures of lanthanide ruthenates (Ln(3)RuO(7)) and osmates (Ln(3)OsO(7)) in the literature. The disorder includes a dynamical or static distribution of one-third of Gd atoms in the unit cell, which is presumably linked to the libration of the octahedral tilts about the axes close to c.     

Thermal conductivity of LiKSO4 near its high-temperature phase transition

The crystallization processes of Ge _x S_1–x glasses were studied by means of heat flux DSC. It was shown that germanium disulphide crystallizes atx1/3. On the other hand, a higher germanium content (x>1/3) led to the crystallization of both GeS₂ and GeS. Kinetic analysis of the processes of crystallization of the studied glasses was performed using the Arrhenius rate constant and the esták-Berggren kinetic model. The kinetic parameters were calculated through non-linear regression of the experimental DSC curves.

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Zusammenfassung Die Kristallisationsprozesse von Gläsern Ge_xS₁–x wurden durch Wärmefluss-DSC untersucht. Beix0,33 kristallisiert GeS₂, während bei höherem Germaniumgehalt (x>0,333) Kristallisation von GeS₂ und GeS eintritt.Für die kinetische Analyse des Kristallisationsprozessen wurden Arrhenius-Geschwindigkeitskonstanten und das esták-Berggren-Modell verwendet. Die kinetischen Parameter wurden durch nichtlineare Regression der experimentellen DSC-Kurven berechnet.

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GexS1–x. , 1/3 , (>1/3) — , . . . .

     

Spectroscopic investigations of phase transition in 5-chloro-2-pyridone

Spectroscopic investigation of 5-chloro-2-pyridone has been carried out in the temperature range 77–300 K. At room temperature the ³⁵Cl NQR spectrum shows a single line at 35.618 MHz, but at 250.7 K two lines appear at 35.850 MHz and 35.840 MHz respectively indicating the presence of a phase transition. IR, far-IR, laser Raman and dielectric measurements have been carried out to investigate the phase transition further. Low temperature IR studies show splitting of ν(CCl), β(NH) and ν(CO) bands at T_c. Dielectric measurements show a small, but finite, change in the value of the dielectric constant around T_c. Raman spectra at different temperatures support the existence of a new phase, as shown by the appearance of a new band at 81 cm⁻¹, the frequency of which changes slowly as T_c is approached and which disappears at T_c. The temperature dependence of the NQR frequencies has been analysed using Bayer Kushida and Brown equations toevaluate the torsional frequencies.     

Gd5-xYxTt4 (Tt = Si or Ge): effect of metal substitution on structure, bonding, and magnetism

A crystallographic study and theoretical assessment of the Gd/Y site preferences in the Gd 5- x Y x Tt 4 ( Tt = Si, Ge) series prepared by high-temperature methods is presented. All structures for the Gd 5- x Y x Si 4 system belong to the orthorhombic, Gd 5Si 4-type (space group Pnma). For the Gd 5- x Y x Ge 4 system, phases with x < 3.6 and x >or= 4.4 adopt the orthorhombic, Sm 5Ge 4-type structure. For the composition range of 3.6 相似文献   

Employing halogen-halogen interaction to construct high-temperature hybrid perovskite phase transition materials

Organic-inorganic hybrid perovskites (OIHPs) materials with high phase transition temperature (T_p) have been widely studied in the field of molecular switches, solar energy and electric power. At present, the OIHPs with high T_p are generally constructed through molecular design, which can be applied to a wide temperature range. Here, three one-dimensional (1D) OIHPs [R-ClEQ]PbCl₃ (T_p = 442 K), [R-ClEQ]PbBr₃ (T_p= 499 K) and [R-ClEQ]PbI₃ (T_p above m.p.) (R-ClEQ = (R)-N-chloroethyl-3-quinuclidinol) with different T_p are obtained by regulating the halogen-halogen interaction and hydrogen bonding in the system. Especially in [R-ClEQ]PbX₃ (X = Cl, Br and I) crystal system, all the halogen bonds tend to form at approximately 180°angles and the strength of halogen bonding is found to be increased from 1.59 × 10^–3 Hartree to 2.35 × 10^–3 Hartree with increased atom number from Cl to I. The synergistic effect of halogen bonding and hydrogen bonding provide a useful strategy for the design OIHPs phase transition materials with high T_p.     

Vacancy ordering in SmGe2-x and GdGe2-x (x = 0.33): structure and properties of two Sm3Ge5 polymorphs and of Gd3Ge5

The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. alpha-Sm3Ge5 and beta-Sm3Ge5 and Gd3Ge5 have been prepared from the corresponding elements through high-temperature reactions using the flux-growth method. The structures of the three compounds have been established using single-crystal X-ray diffraction: alpha-Sm3Ge5 crystallizes with its own type in the hexagonal space group P2c (No. 190) with cell parameters a = 6.9238(11) A, c = 8.491(3) A, and Z = 2, whereas beta-Sm3Ge5 adopts the face-centered orthorhombic Y3Ge5 type with space group Fdd2 (No. 43) and with cell parameters a = 5.8281(6) A, b = 17.476(2) A, c = 13.785(2) A, and Z = 8. The orthorhombic Gd3Ge5 with cell parameters a = 5.784(2) A, b = 17.355(6) A, and c = 13.785(5) A is isostructural with beta-Sm3Ge5. The structures of the title compounds can be described as AlB(2) and alpha-ThSi2 derivatives with long-range ordering of the germanium vacancies. Temperature-dependent DC magnetization (5-300 K) measurements show evidence of antiferromagnetic ordering below ca. 30 and 10 K for alpha-Sm3Ge5 and beta-Sm3Ge5, respectively. Gd3Ge5 undergoes two successive magnetic transitions below ca. 15 and 11 K. The temperature dependence of the resistivity and heat capacity of Gd3Ge5 are discussed as well.     

On the phase transition of acetylene-d2

The solid-solid phase transition of acetylene-d₂ at 149 ± 1 K was investigated using a thermal neutron powder diffraction technique. Due to a rapid recrystallization in the vicinity of the transition point the study of the kinetics of the transition was not successful.     

Use of a summation technique for evaluation of the phase transition in lead germanate,Pb5Ge3O11

A computer technique is outlined to increase the signal: noise ratio of DSC results for transformations involving small changes of energy. The method is applied to determine the transformation temperature of the ferroelectric-paraelectric transformation of lead germanate, Pb₅Ge₃O₁₁, either pure or doped with Nd³⁺ or with Nd³⁺+K⁺.

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Zusammenfassung Eine Computermethode wird angegeben, die es erlaubt, das Signal: Rausch-Verhältnis bei DSC-Messungen von Umwandlungen mit geringer Energie zu erhöhen. Diese Methode wird verwendet, um die Temperatur der Umwandlung ferroelektrisch-paraelektrisch an Bleigermanat Pb₅Ge₃O₁₁, rein oder dotiert mit Nd³⁺ oder mit Nd³⁺ +K⁺, zu bestimmen.

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Thanks are due to Dr. H. D. Kürsten, who prepared the crystals.     

Cluster self-organization of silicate and germanate systems: Suprapolyhedral precursor nanoclusters and self-assembly of tetrahedral structures of the family A2T2O5 (A = Li, Na; T = Si, Ge): Li2T2O5, Li4Ge3SiO10, Li2Si2O5, and A2Si2O5

Modeling of atomic species (An clusters in the form of atoms or Kn polyhedra, where n is the number of atoms or polyhedra) corresponding to the initial stage of evolution of a chemical system has been carried out. Three series of K4 clusters built of different T tetrahedra (L and T) have been recognized. For L₂T₂ clusters, six geometrically and symmetrically different types of suprapolyhedral clusters have been discovered. The model has been used to identify precursor clusters in A₂T₂O₅ (A = Li, Na; T = Si, Ge) framework structures: A-type Li₂T₂O₅ with space group Cc, B-type Li₄Ge₃SiO₁₀ with space group Abm2, C-type Li₂Si₂O₅ with space group Ccc2, and D-type A₂Si₂O₅ with space group Pbcn. Three (of the six possible) types of suprapolyhedral precursor nanoclusters K4 in the four structures have been identified. The full 3D reconstruction of the self-assembly scenario of crystal structures is as follows: precursor nanocluster ?? primary chain ?? microlayer ?? microframework ?? ?? framework. The bifurcation of structural evolution pathways (structural branching points) at the suprapolyhedral level for type A and B structures is found to occur only when a microframework is formed of equivalent microlayers.     

Gd2CuO4薄膜与Si, SiO2/Si基底界面相互作用研究

采用XRD和俄歇电子能谱（AES）等技术研究了钙钛矿型Gd2CuO4薄膜与基底Si和SiO2/Si的界面相互作用,发现衬底对Gd2CuO4薄膜的晶化特性有很大影响,以单晶Si为基镀时,Gd2CuO4薄膜经600℃热处理1h即可形成钙钛矿型晶体结构,而以SiO2/Si为基底时,经700℃热处理1h能形成较完善的钙钛矿型晶体结构,Gd2CuO4薄膜的晶粒度随热处理温度的升高而增大,热处理时间对晶粒度则影响较小,AES深度剖析表明,形成的薄膜组成均匀,在界面上有一定程度的扩散,以Si为基底时,Gd2CuO4与基底Si相互扩散,以SiO2/Si为基底时则主要是薄膜中Gd,Cu向SiO2层中的扩散,AES线性分析表明,在薄膜与基底的界面上,各元素的俄歇电子动能发现位移,表明基底作用使界面上元素的化学环境发生了变化。     

On the percolative character of the liquid-glass phase transition

Mutual arrangement of atomic cells (defined as Voronoi polyhedra) in a large volume is studied by percolation analysis on the Delaunay network in terms of molecular dynamic models of Lennard-Jones liquids, crystals, and amorphous solids. Characteristics of percolative clusters as well as percolation thresholds proved to be almost the same for all the phases. From this it is inferred that the liquid-glass phase transition is not due to percolation over regions with large free volume. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Korean Institute of Advanced Science and Technology. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp. 473–480, May–June, 1995 Translated by L. Smolina