Magnetic properties and magnetic structure of the Mn5Si3-type Tb5Si3 compound

Neutron diffraction and magnetization measurements have been performed on the Tb₅Si₃ compound (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at on cooling. However, the magnetization data depict two transitions at 72 K (T_N1) and 55 K (T_N2). The extended temperature range between and over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at T_N1 and low-temperature antiferromagnetic transition at T_N2 of the magnetic data. Between Tb₅Si₃ shows a flat spiral antiferromagnetic ordering with a propagation vector K₁ = [0,0, ±1/4]; then, between the flat spiral type ordering is conserved, but by two coexisting propagation vectors K₁ = [0,0, ±1/4] and K₂ = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below the magnetic component with K₁ = [0,0, ±1/4] vanishes and magnetic structure of Tb₅Si₃ is a flat spiral with K₂ = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of 3 T.     

The magnetic ordering in the Ho5Si3 and Ho5Ge3 compounds

A neutron diffraction investigation has been performed on the Ho₅Si₃ and Ho₅Ge₃ compounds (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic orderings (T_N1 and T_N2).Between T_N1 = 24(2) and T_N2 = 16(4) K Ho₅Si₃ shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K₁ = [0, 0, ±0.284(1)]; then, below T_N2 the sine-modulated type ordering is conserved, but by the two propagation vectors K₁ = [0, 0, ±0.2773(7)] and K₂ = [±1/5, ±1/5, 0].For Ho₅Ge₃, between T_N1 = 27(2) and T_N2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K₁ = [0, 0, ±3/10] and K₂ = [0, 1/2, 0], whilst below T_N2 the ordering takes place with propagation vectors K₁ = [0, 0, ±3/10], K₂ = [0, 1/2, 0], K₃ = [0, 0, ±2/5] and K₄ = [±1/5, ±1/5, 0]. For both the Ho₅Si₃ and Ho₅Ge₃ compounds, the dimensions of the magnetic unit cell are 5a × 5a × 10c times the crystal unit cell of Mn₅Si₃-type.     

MoSi2—Mo5Si3复合材料的低温氧化行为

通过热重分析（TGA）、X射线衍射（XRD）和扫描电镜（SEM）研究了MoSi2-Mo5Si3复合材料的低温氧化行为,指出材料低温氧化时,随Mo5Si3量增多,材料氧化加剧,当Mo5Si3含量超过16％（质量分数）时发生“PEST”现象,所形成的SiO2由于MoS3晶须的大量存在,使其不能均匀连续地分布于材料表面,从而加剧了氧化。     

Evidence for the existence of Hf5Si3

This article describes new evidence for the existence of Hf₅Si₃ with the Mn₅Si₃ structure type (hP16-P6₃/mmc). Binary Hf-Si alloys with Si concentrations from 11.5 to 35.0 at.% were investigated. Hf₂Si was also observed in the binary Hf-Si alloys that were investigated; this is consistent with the assessed phase diagram. The Mn₅Si₃-type structure has been observed in both binary Hf₅Si₃ and higher alloyed forms, (Hf, X)₅Si₃, where Nb and Ti were substituted for Hf. Phase identification was performed using scanning electron microscopy, electron microprobe analysis, x-ray diffraction, and automated electron backscattering pattern analysis in the scanning electron microscope. The present data indicate that high levels of O, N, or C are not required to stabilize Hf₅Si₃, and that it can exist alone as a binary compound. This result is contrary to previous reports regarding Hf₅Si₃, which claim that it only exists when stabilized by interstitials.     

Phase relationships and crystallography in the pseudobinary system Gd5Si4---Gd5Ge4

A study of phase relationships and crystallography in the pseudobinary system Gd₅(Si_xGe_1−x)₄ revealed: (1) that both terminal binary compounds Gd₅Si₄ and Gd₅Ge₄ crystallize in the Sm₅Ge₄-type orthorhombic structure, and (2) the appearance of an intermediate (ternary) phase with a monoclinic crystal structure which is similar to both Gd₅Si₄ and Gd₅Ge₄. The formation of the monoclinic phase at 0.24≤x≤0.5 [between Gd₅(Si_0.96Ge_3.03)Gd₅(Si₁Ge₃) and Gd₅(Si₂Ge₂)] is probably due to the large difference in bonding characteristics of Si and Ge in the Gd₅Si₄-Gd₅Ge₄ pseudobinary system which limits the ability of the mutual substitution of Si for Ge and vice versa without a change of the crystal structure. For the composition Gd₅(Si₂Ge₂) the lattice parameters of the monoclinic structure (space group P112₁/a) are a=7.580865), b=14.802(1), c=7.7799(5)Å, γ=93.190(4)°. A distinct difference in the magnetic behaviors of the alloys from three different phase regions in this system follows the distinct difference in the crystal structures observed for the alloys from the three phase regions.     

Magnetocaloric effect in Pr6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Pr₆Co_1.67Si₃ compound have been investigated by magnetization measurements. The saturation moment at 5 K is found to be 10.7μ_B. The compound undergoes two magnetic transitions below Curie temperature T_C = 48 K and shows a reversible second-order magnetic transition around T_C. A magnetic entropy change ΔS = 6.9 J/(kg K) is observed for a magnetic field change from 0 to 5 T. The full width at half maximum of the ΔS peak is found to be about 38 K.     

Synthesis and crystal structure of Ba3Si4C2

SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba₃Si₄C₂. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba₃Si₄C₂ has the Ba₃Ge₄C₂ type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO₃), and contains isolated anion groups of slightly compressed [Si₄]⁴⁻ tetrahedra and [C₂]²⁻ dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10⁻²–7 × 10⁻³ S cm⁻¹ in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K⁻¹.     

High-temperature SO2-gas corrosion of TiN–Ti5Si3 composites prepared by polymer pyrolysis

By pyrolyzing a mixture of Si-containing pre-ceramic polymers and TiH₂ powders in a N₂ atmosphere, a TiN–Ti₅Si₃ composite was synthesized. The composite was then corroded between 700 °C and 1000 °C for 20 h in an Ar–0.2% SO₂ atmosphere. TiN was mainly oxidized to rutile TiO₂. Ti₅Si₃ was oxidized to TiO₂ supersaturated with Si ions, and sulfidized to Ti₂S supersaturated with Si ions. At initial stage of corrosion, oxidation dominated sulfidation. As corrosion proceeded, sulfidation progressively occurred underneath the oxide scale based on the decreased oxygen potential and increased sulfur potential near the scale/matrix interface.     

Growth and dielectric properties of Ca3NbGa3Si2O14 crystals

A new langasite type single crystal Ca₃NbGa₃Si₂O₁₄ (CNGS) was grown by Czochralski (CZ) method. The structure of CNGS crystal was determined by X-ray powder diffraction, the lattice parameters were a=0.8087 ± 0.0001 nm, c=0.4974 ± 0.0002 nm, V=0.2817 ± 0.0002 nm³; The congruency of CNGS was examined by measuring the chemical composition of the grown crystal by quantitative X-ray fluorescent (XRF) analysis. The melting point of CNGS crystal was measured by using the differential scanning calorimetry (DSC). Dielectric properties of (1 1 0) wafer plate were studied in the temperature range from 298.15 to 873.15 K; the frequency dependence of dielectric loss in the frequency range 10 Hz–13 MHz was measured.     

The influence of gallium on the magnetocaloric properties of Gd5Si2Ge2

Gd₅Si₂Ge₂ was alloyed with varying amounts of Ga to study its influence on the giant magnetocaloric effect. Investigations on Gd₅(Si_2−xGe_2−x)Ga_2x with 2x = 0.03, 0.05 and 0.13 were carried out using X-ray powder diffraction, temperature and magnetic field dependent magnetization measurements, and differential scanning calorimetry. We observe that as the Ga content increases, the temperature stability range of the monoclinic phase narrows, and the orthorhombic structure gains stability. This is expected to be related to the decrease in the (Si/Ge)(Si/Ge) bond distance in the monoclinic phase. The maximum entropy change for the parent compound at 270 K was found to be 9.8 J kg⁻¹ K⁻¹ in an applied field of 5 T. For 2x = 0.03, this value reduces to 8.5 J kg⁻¹ K⁻¹, and the temperature corresponding to the maximum entropy change shifts marginally to 278 K. For other 2x values, the maximum entropy change further decreases.     

Crystal structures of new ternary rare earth silicides Sc3Pr2Si4, Sc1.26Pr3.74Si4 and Sc3.96Nd1.04Si4 with ordered and partially ordered rare earth sites

The crystal structures of three new ternary silicides Sc₃Pr₂Si₄, Sc_1.26Pr_3.74Si₄ and Sc_3.96Nd_1.04Si₄ were determined by single crystal X-ray diffraction. The title compounds crystallize with three different substitution derivatives of the Sm₅Ge₄ structure type (orthorhombic space group Pnma) containing various distributions of rare earth atoms on the three Sm sites. Crystal chemistry analysis shows that these distributions are controlled by the atomic size factor.     

Novel silicide BaPt5Si12: Crystal structure and physical properties

BaPt₅Si₁₂ has been synthesized by argon arc melting the elements. The structure was solved by direct methods from Kappa CCD intensity data. The novel silicide crystallizes in a unique monoclinic structure type: space group C2/m; a = 0.61327(2) nm, b = 3.23481(8) nm, c = 0.61180(1) nm, β = 90.130(2)°. The structure of BaPt₅Si₁₂ is characterized by Pt atoms, which are all arranged in planes parallel x–z resulting in tetrahedral coordination for Si1, Si2, Si3 and Si4 atoms and more complex distorted polyhedra around Si5 and Si6 atoms. Three voids were encountered in the structure at the centres of an Achimedian antiprism and two cube-octahedra. These voids do not show any residual electron densities. BaPt₅Si₁₂ turns out to be metallic; no phase transitions are found within the temperature range from 300 mK to 300 K. The overall resistivity is rather large, presumably a consequence of the voids in the crystal structure. Additionally, the quite complex crystal structure gives rise to intricate phonon modes.     

High-field magnetization of a Dy2Fe14Si3 single crystal

The magnetization of a Dy₂Fe₁₄Si₃ single crystal was measured at 4.2 K in pulsed fields up to 51 T along the principal axes. The compound orders ferrimagnetically at 500 K, has a spontaneous magnetic moment of 8 μ_B/f.u. (at 4.2 K) and exhibits a very large magnetic anisotropy, 〈1 0 0〉 being the easy axis. In fields applied along the 〈1 0 0〉 and 〈1 2 0〉 axes, field-induced phase transitions are observed at 33 T and at 39 T, respectively. The c-axis magnetization curve crosses the easy-axis curve at 19 T. At higher fields, for all directions, the magnetization continues to increase due to further bending of the sublattice moments. Temperature evolution of magnetic anisotropy and magnetic hysteresis are discussed as well.     

退火对(Mo1-xNbx)5Si3高温合金组织与力学性能的影响

采用电弧熔炼结合高温退火技术制备(Mo1-xNbx)5Si3(其中,x=0.0,0.2,0.4,0.6,0.8,1.0)系高温合金,研究了退火处理对其组织和性能的影响.结果表明:退火使合金组织趋于均匀化,Mo的加入使Nb5Si3合金的组织由α型向β型转变;退火前后试样的硬度均呈先增高后降低的抛物线规律,退火后试样的硬度高于退火前的硬度;断裂韧性呈先降低后升高的规律:断口主要以脆性断裂为主.     

Development and oxidation resistance of air plasma sprayed Mo-Si-Al coating on an Nbss/Nb5Si3 in situ composite

A Mo-Si-Al coating, which is mainly composed of Mo(Si,Al)₂ and Mo₅(Si,Al)₃, was developed to protect a Nb_ss/Nb₅Si₃ in situ composite by air plasma spraying. After oxidation at 1250 °C, the oxidation curve followed parabolic law and even after oxidation for 100 h, the weight gain of Mo-Si-Al coating was 8.24 mg/cm². The surface of the oxidized samples became flatter and smoother as time increased due to the formation of SiO₂ glass. Moreover, the microstructure of Mo-Si-Al coating changed and a layer structured interdiffusion zone was formed at the substrate-coating interface after oxidation.     

The crystal structure of the novel ternary silicide Sm4Pd4Si3

The crystal structure of the compound Sm₄Pd₄Si₃ was determined by the single-crystal method (KM-4 automatic diffractometer, Mo K radiation. Sm₄Pd₄Si₄ has the monoclinic Nd₄Rh₄Ge, type structure: space C2/c, mC44 (No. 15). a = 20.693(6), B = 5.584(1), C = 7.699(2) Å, β = 109.48(3)°, V = 838 Å, Z = 4, μ - 36.23 mm¹, R =_F = 0.0537, R _F = 0.0435 for 1652 unique reflections. The coordination numbers of samarium atoms are 17 and 18. For palladium and silicon atoms icosahedra and trigonal prisms with additional atoms are typical as coordination polyhedra. The structure of Sm₄Pd₄Si₄ is composed of fragments of the YPd₂Si and Y₁Rh₂Si₂ structure in a ratio 1:1.     

New ternary aluminides T5M2Al having W5Si3-type structure

Six new ternary aluminides having W₅Si₃-type structure were found. These are: Zr₅Sn₂Al, Hf₅Sn₂Al, Ti₅Pb₂Al, Zr₅Pb₂Al, Hf₅Pb₂Al and Nb₅Sn₂Al.     

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti₅Si₃ in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti₅Si₃ composites had a high microhardness of 980.3HV_0.2, showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti₅Si₃ composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10^− 4 mm³/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.     

Hf6Ta2O17材料的合成和热膨胀性能

以HfO2、Ta2O5粉体为原料,采用固相法合成Hf6Ta2O17材料。在空气气氛下1600℃常压烧结8h制备块体试样。用X射线衍射(XRD)仪检测合成粉体的相结构,通过场发射扫描电镜(SEM)观察试样的微观形貌,用热膨胀仪检测试样的热膨胀系数(TEC)。结果表明:固相法可以制备纯净单相的Hf6Ta2O17材料和比较致密的块体试样;Hf6Ta2O17材料在20~1400℃温度范围内没有相变,其高温相稳定性优于YSZ材料;Hf6Ta2O17在1200℃的热膨胀系数为9.59×10-6/℃,与YSZ材料的热膨胀系数接近,有望用于热障涂层。     

Interstitial solid solution Hf5GaxSn3 (x = 0-1)

Formation of an interstitial solid solution Hf₅Ga_xSn₃ (x = 0-1) based on the binary compound Hf₅Sn₃ (structure type Mn₅Si₃, Pearson symbol hP16, space group P6₃/mcm, a = 8.36562(6), c = 5.70775(4) Å from X-ray powder diffraction) was established at 600 °C. The crystal structure (structure type Hf₅CuSn₃, ordered derivative of Ti₅Ga₄, hP18, P6₃/mcm) was refined on X-ray single-crystal diffraction data for three compositions: Hf₅Ga_0.16(3)Sn₃ (a = 8.3288(12), c = 5.6988(11) Å), Hf₅Ga_0.53(2)Sn₃ (a = 8.4205(12), c = 5.7655(12) Å) and Hf₅GaSn₃ (a = 8.5564(12), c = 5.7859(12) Å). The Ga atoms occupy Wyckoff position 2b at the centres of Hf₆ octahedral interstices.