Sb Phase Research Articles

Crystallization behavior and electrical characteristics of Ga–Sb thin films for phase change memory

In this work, we investigated the structural and conductivity stability of Ga–Sb thin films for phase change memory (PCM). The mass density and thickness change are significant for stability and reliability of PCM. The Ga–Sb thin films were deposited on SiO2/Si (100) wafer using magnetron co-sputtering method. Phase identification revealed that nanoscale face center cubic structure GaSb and rhombohedral structure Sb formed in Ga–Sb thin films, the formation of phase Sb was more obvious in Ga20Sb80. Ga–Sb film exhibits an unusual behavior upon crystallization with less mass density and thickness change. The microstructure of Ga45Sb55 thin films improved their structural (density and film thickness) characteristics: the crystal growth of {111} and {110} oriented grains in Ga–Sb thin films is obvious, the grains growth in Ga45Sb55 thin films was more even and the bonding states in Ga–Sb thin films were more stable. In addition, the conductivity activation energy of Ga–Sb decreased with increasing Sb contents, thus the temperature stability of conductivity was improved. The structure transformation and conductivity activation energy of Ga–Sb phase change materials are in favor of mechanical stresses reduction and reliability enhancement of PCM. This study introduces the influence mechanism of structural and conductivity stability in Ga–Sb thin films and may provide reference for further testing in higher endurance performance phase change materials.

Mixing Enthalpies of Sr–Sb Melts

The mixing enthalpies of Sr–Sb melts were measured by isoperibolic calorimetry at 1230 K over the entire composition range referred to the liquid components. Large exothermic mixing effects were found (∆Hmin = –70.1 ± 4.8 kJ/mole). They were indicative of very strong interaction between the components and agreed with the Sr–Sb phase diagram. A series of intermetallic compounds, SrSb, SrSb3, Sr3Sb2, and Sr2Sb, was found in the system. Minimum ∆H for the liquid alloys corresponds to the composition range where SrSb and Sr3Sb2 phases exist. The mixing enthalpies were found to be less exothermic than those for the intermetallic phases. This finding agrees with data for the alloys in systems with strong interaction between the components and is indicative of short-range ordering in liquid state. The mixing enthalpies for Mg (Ca, Sr)–Sb melts decrease in the Mg–Sb → Ca–Sb → Sr–Sb series, which agrees with increasing differences in the electronegativity of the components.

Modifying structural polymorphs and tuning electronic properties in pressure-stabilized binary Ir-Sb phases.

The search for novel structures and chemical stoichiometry of binary Ir–Sb compounds is of great importance in view of their catalytic applications. Based on the results of swarm structure searching technique combined with density functional theory, we proposed the hitherto unknown Ir–Sb phase diagram in a wide pressure range with various chemical compositions. Besides two ambient pressure phases of IrSb3-Im3̄ and IrSb2-P21/c, five novel phases of IrSb-C2/c, IrSb-P1̄, IrSb2-P4̄21m, IrSb2-I4/mmm and Ir2Sb-Pmmn were identified at high pressures. The phonon dispersion curves reveal that these phases are all dynamically stable. The calculated electronic results show that a mixed behavior of covalent, ionic and metallic bonds simultaneously exits in these novel phases. A pressure-induced electronic topological transition in Ir2Sb-Pmmn phase occurs according to the theoretical electronic band structures, while is not shown in other stoichiometries of the Ir–Sb system. Our work provides a potential opportunity for experimental synthesis of crystal structures with different chemical stoichiometries of the binary Ir–Sb system.

Improved Mechanical and Electrical Properties of Phase-Change-Memory Ga-Sb Thin Films.

In this study, we focus on the mechanical and electrical properties of Ga-Sb thin films with different Sb contents; the corresponding improvement mechanism is also discussed. The phase-identification results prove that cubic GaSb phase and rhombohedral Sb phase exist in crystalline Ga-Sb thin films. Moreover, elemental Ga formed in small sizes around the boundary was observed. The resistance-temperature curves prove that the crystallization temperature (Tx) of Ga-Sb is 40 °C higher than that of Ge₂Sb₂Te5 (GST), and that Tx increased with increasing Ga content, while the resistance contrasts decreased. Consequently, the amorphous thermal stability of Ga-Sb is superior. Nanoindentation results prove that the hardness and elasticity modulus of Ga-Sb increases with increasing Ga content and is higher than that of GST thin films. In addition, structural investigation demonstrated that with different Ga contents, the hardness improvement of Ga-Sb thin films benefits from grain-size effects and the precipitation of elemental Ga in grain boundaries. Therefore, the ratio of Ga and Sb content has a different influence on the properties of both constituents. These findings indicate that binary Ga-Sb compositions are promising candidates for phase-change-memory applications.

Zn-doped Sb70Se30 thin films with multiple phase transition for high storage density and low power consumption phase change memory applications

The single layer Zn44Sb39Se17 thin film, being fabricated by Sb70Se30 and Zn using co-sputtering method, exhibits double phase change transition. The double phase change processes are mainly attributed to the crystallization of the Sb and ZnSb phases. The potential operating temperature for ten years of two phase change processes are 64 °C and 179 °C, of which the good stability of the second phase change can be sufficient for the autoelectronic applications. Meanwhile we also discovered the Zn44Sb39Se17 thin film presents apparent low power consumption in comparison with Ge2Sb2Te5 and other reported Sb-Se based phase change materials.

Natural attenuation of antimony and arsenic in soils at the abandoned Sb-deposit Poproč, Slovakia

This contribution investigates the natural attenuation of arsenic (As) and antimony (Sb) in highly contaminated soils at the abandoned Sb-deposit Poproc in eastern Slovakia. The studied soils were identified as technosols with pH values of 3.5–7.0 and high metal and metalloid load: antimony, arsenic, lead, and zinc up to 5757, 2484, 683, and 407 mg/kg, respectively. These toxic elements occur in the soils mainly as constituents of secondary minerals, which are products of sulphide oxidation. Bulk correlation between Fe and As is weak (p > 0.05), but inspection of micro-X-ray fluorescence maps shows that the secondary iron oxides are always associated with elevated As. Electron microprobe (EMP) and micro-X-ray diffraction analyses showed significant chemical and mineralogical heterogeneity of the secondary minerals, with wide variations of their Fe/Sb ratio and occasionally elevated Ca and Pb (> 5 wt%). The most common secondary minerals are goethite (α-FeOOH) with concentrations of Sb up to 3.14 wt% and As (1.29 wt%) and tripuhyite (FeSbO4) with increased content of As (1.14 wt%). Sb-rich secondary phases were identified as valentinite/senarmontite (Sb2O3), cervantite (Sb2O4), and a pyrochlore-group mineral stibiconite. High Sb phases with increased concentrations of Ca (up to 6.48 wt%) or Pb (20.78 wt%) were identified as stibiconite (EMP). This study shows that the secondary mineralogy in naturally attenuated contaminated soils and in Sb-containing tailings is identical. Hence, such tailings achieve their final state with respect to the Sb minerals within decades and are unlikely to change further.

Experimental study and thermodynamic re-assessment of the Co–Sb system

The Co–Sb system is of a special attention due to existence of CoSb3 skutterudite structure which is the key structure for doped skutterudite based thermoelectric materials. A critical review of this system, performed recently, shows the published thermodynamic assessment may not be fully correct compared to existing studies. Especially, there is a contradiction in the position of the liquidus line on the Sb-rich side of the phase diagram and of the eutectic reaction, liquid ↔ CoSb3 + (Sb). As these data are crucial for the study of thermal stability of skutterudite based thermoelectric materials, a good knowledge on phase relations in the Sb-rich part of the Co–Sb phase diagram is needed. To obtain reliable data, experimental alloys covering 80 to 100 at.% of Sb were prepared and investigated by differential thermal analysis and phase analysis. The data were compared with existing literature information and thermodynamic re-assessment of this binary system based on the CALPHAD approach was done.

Phase-change characteristics of carbon-doped GeSbSe thin films for PRAM applications

Phase-change random access memory (PRAM) is a promising way to overcome problems associated with dynamic random access memory and flash memory, namely, scaling them down to meet increasing performance and reliability demands. Herein, we evaluate carbon-doped Ge10Sb90Se8 (GSS-C) as a potential chalcogenide material for PRAM. The carbon-doping effects on the physical and electrical properties of GSS film were investigated at carbon concentrations from 0 to 11 at.%. The crystal structures were analyzed via X-ray diffraction, which demonstrated that the undoped GSS films had multiple phases; however, incorporating carbon led to a single phase with a rhombohedral crystal structure (Sb phase). The grain size and change in thickness upon phase transition both decreased with increasing carbon concentration, whereas the crystallization temperature and sheet resistance of the amorphous and crystalline states increased. X-ray photoelectron spectroscopy revealed that adding carbon leads to the formation of C–Ge and C–Sb bonds. Moreover, as the carbon concentration increased, the on/off ratio and optical band gap increased. These results imply that GSS-C possesses advantageous thermal stability, reliability, and electrical properties, which strongly suggest that GSS-C would be a promising candidate for phase-change memory applications.

Ultrafast crystallization in nanoscale phase change film of monobasic antimony

The property of Sb phase change thin film is investigated systematically. Sb thin film has an appropriate crystallization temperature (~165 °C) and data retention (110 °C for 10 year). Irradiated by laser pulse, the Sb thin film can achieve the crystallization operation within 6.05 ns. The monoclinic structure is confirmed by X-Ray Diffraction and the bond vibration mode of A7 phase is demonstrated by Raman scattering spectrum. With the crystallization, the band gap becomes narrow and the polycrystalline structure gradually forms. The Sb-based phase change memory cells are prepared. An ultrafast programing operation (~5 ns) and good endurance of 1.4 × 107 cycles are achieved. The results reveal that Sb thin film has promising potential in phase change memory application.

Insulator–metal transition and ultrafast crystallization of Ga40Sb60/Sn15Sb85 multiple interfacial nanocomposite films

The phase change behavior of Ga40Sb60/Sn15Sb85 multiple interfacial film was studied systematically for its application in phase change memory. The thermal stability of amorphous state was evaluated using the Arrhenius formulas. The evolution of phase structure indicates that the Sb phase exists in the Sb-rich Ga40Sb60/Sn15Sb85, Ga40Sb60 and Sn15Sb85 films. The change in density and thickness during crystallization was obtained by X-ray reflectance. The nanoscale change in roughness of the Ga40Sb60/Sn15Sb85 film was confirmed by atomic force microscopy. The rate for crystallization and amorphization transformation was measured by a picosecond laser pump-probe system. The phase change memory device based on [Ga40Sb60 (7 nm)/Sn15Sb85 (3 nm)]5 thin film was fabricated. An ultra-fast switching and low power were achieved for Ga40Sb60/Sn15Sb85 multiple interfacial film.

Boundaries of the X Phases in Sb–Te and Bi–Te Binary Alloy Systems

Sb–Te and Bi–Te compounds are key components of thermoelectric or phase change recording devices. These two binary systems form commensurately/incommensurately modulated long-period layer stacking structures known as homologous phases that comprise discrete intermetallic compounds and X phases. In the latter, the homologous structures are not discrete but rather appear continuously with varying stacking periods that depend on the binary composition. However, the regions over which these X phases exist have not yet been clarified. In this study, precise synchrotron X-ray diffraction analyses of various specimens were conducted. The results demonstrate that the X phase regions are located between Sb20Te3 and Sb5Te6 in the Sb–Te system and between Bi8Te3 and Bi4Te5 in the Bi–Te system.

Insight into the role of nitrogen in the phase-change material Sb

The influence of nitrogen dopant on the structure of the phase-change material Sb has been investigated by ab initio molecular dynamics simulations. The doped N exist as SbN complex in amorphous phase and would not enter into the rhombohedra phase of crystalline Sb. During crystallization of the amorphous phase, no N2 molecule is formed and part of the N–Sb bonds are broken to release Sb atoms which contribute to growth of crystal nuclei by forming more Sb–Sb bonds. Remaining N–Sb bonds would segregate at the grain boundaries and retard growth of crystal nuclei.

The impact of vacancies on the stability of cubic phases in Sb\u2013Te binary compounds

Data retention ability and number of cycles are key properties of phase change materials in applications. Combining in situ heating transmission electron microscopy with ab initial calculations, we investigated the phase transitions of binary Sb–Te compounds. The calculations indicated that the vacancies in Te sites destroyed the framework of the cubic phase, which agrees well with the absence of cubic phases observed during in situ heating experiments when the Sb concentration exceeded 50%. In contrast, the vacancies in Sb sites stabilized the cubic structure. Further analysis of the charge density maps revealed that the distribution of antibonding electrons may be the origin of the driving force for structural transitions. Furthermore, our results also showed that reducing the vacancies greatly increased the phase transition temperatures of both the amorphous-cubic and cubic-trigonal phases and therefore may improve the data retention ability and cyclability of phase change materials. This result also implies that doping Sb–Te compounds may provide an approach to discover novel phase change materials by reducing the amount of vacancies.

Effects of sintering temperature on microstructure and thermoelectric properties of Ce-filled Fe4Sb12 skutterudites

The improvement of thermoelectric properties of p-type iron-based skutterudites is limited due to the present of more iron-rich impurity phases induced by the inherent structural instability of Fe-containing skutterudites. How to reduce the content of the impurity phase in p-type Fe-based skutterudites is a key to obtain high ZT value. Ce1.25Fe4Sb12 materials with different sintering temperatures (723 K, 773 K, 798 K, 823 K and 848 K) have been prepared by a traditional melting-quenching-annealing process coupled with spark plasma sintering (SPS) technique. The results of XRD and EPMA analysis indicate that all the SPSed samples consist of the main skutterudite phase and impurity phases of FeSb2, Sb, CeSb2 and oxides of Ce and Sb. Compared with other SPSed samples, the SPS-773 K sample has the best thermoelectric properties due to the relatively fewer impurity phases, a large number of micro-nanoscale particles at the grain boundary and more voids. The SPS-773 K sample shows the largest ZT value over the entire test temperature range due to the higher power factor and lower lattice thermal conductivity. The maximum ZT value reaches 0.81 at 800 K. This indicates that thermoelectric properties of Ce-filled Fe4Sb12 skutterudite materials can be effectively improved by reducing impurity phases induced by the optimization of the sintering temperature.

Size-Dependent Melting Behavior of Pb-17.5 At. Pct Sb-Free Biphasic Alloy Nanoparticles

The present investigation reports the size-dependent melting behavior of bi-phasic Pb-17.5 at. pct Sb-free alloy nanoparticles, consisting of face-centered cubic (Pb) and rhombohedral (Sb) phases. These free nanoparticles (devoid of matrix) were synthesized via the solvothermal route, and subsequently different sizes were obtained by controlled heat treatment at 373 K under protective Ar atmosphere for the various durations. DSC and in situ TEM studies were used to probe the melting behavior. The experimental results reveal classical behavior, indicating the normalized eutectic temperature was inversely proportional to the nanoparticle radius. The in situ TEM investigation shows that melting initiates at the triple point among (Pb)/(Sb) and an outer surface and subsequently the melt front propagates into (Pb) phase first and then into (Sb) phase. Detailed thermodynamic modeling of the Pb-Sb system with size was carried out to decipher the size-dependent melting behavior of the biphasic nanoparticles. The experimental finding was corroborated with a theoretically predicted phase diagram as a function of size showing a reasonable match.

Superlattice‐like Zn 15 Sb 85 /Ga 30 Sb 70 thin films for low power and ultrafast phase change memory application

In this study, the amorphous-to-crystalline transitions of superlattice-like (SLL) Zn 15 Sb 85 /Ga 30 Sb 70 thin films were investigated by in situ film resistance measurement. The thermal stability, resistance and band gap of the SLL Zn 15 Sb 85 /Ga 30 Sb 70 thin film perform well. The data retention temperature for 10 years increases from 177°C of [Zn 15 Sb 85 7/Ga 30 Sb 70 3] to 220°C of [Zn 15 Sb 85 2/Ga 30 Sb 70 8]. The X-ray diffraction patterns show the presence of a large amount of Sb phase in the Zn 15 Sb 85 /Ga 30 Sb 70 thin films, which causes a rapid phase transition. The surface morphology is observed by atomic force microscopy, which indicates that the thickness of Ga 30 Sb 70 in the SLL thin films can affect the grain size and inhibit the crystallisation process. For the Zn 15 Sb 85 /Ga 30 Sb 70 thin films, an ultra-short switching time of around 2 ns is achieved. These results indicate that the SLL Zn 15 Sb 85 /Ga 30 Sb 70 thin films have a promised application in phase change memory.

Magnetron sputtering deposition of MSb(M=Fe, Ni, Co) thin films as negative electrodes for Li-ion and Na-ion batteries

MSb (M=Fe, Ni, Co) thin films were successfully prepared by magnetron sputtering deposition. The as-prepared MSb (M=Fe, Ni, Co) thin films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), which show that the MSb (M=Fe, Ni, Co) thin films are mixed with different content of Sb phase, and composed of cone-like nanostructures including some plate-like submicroparticles with the size of 100–500 nm. The electrochemical performance indicated that the as-prepared FeSb and NiSb thin films could deliver a high discharge capacity with Li and Na compared with that of CoSb. In addition, the MSb (M=Fe, Ni, Co) thin films also shows a good capacity retention after several ten cycles.

Thermal stability of p-type Ag-doped Mg3Sb2 thermoelectric materials investigated by powder X-ray diffraction.

The thermal stability of the p-type Mg2.985Ag0.015Sb2 material with reported good thermoelectric performance is systematically investigated using powder X-ray diffraction (PXRD). Rietveld refinements were performed to extract the quantitative compositional and structural information from PXRD data. For both densified bulk samples and powdered samples of Mg2.985Ag0.015Sb2 studied under vacuum, a secondary phase, Sb, appears upon the first heating process at temperatures above 500 K, but the amount of the Sb phase stabilizes in subsequent thermal cycles. This is consistent with the good repeatability of the electrical resistivity data after the first cycle measurement, and it indicates that the appearance of the Sb phase does not result in structural decomposition or degradation of the thermoelectric properties. To investigate the effect of the Mg vacancy concentration on the formation of the secondary Sb phase, Mg3.5-xAgxSb2 (x = 0 and 0.015) samples with nominal excess Mg were synthesized and characterized. Compared with Mg2.985Ag0.015Sb2, it is found that Mg3.5-xAgxSb2 (x = 0.015) shows no Sb phase appearing for the bulk sample after heat treatment, and only a small amount of Sb emerges in the powdered sample. This reveals that decreasing the Mg deficiency is beneficial for reducing the amount of emerging Sb secondary phase. In addition, there is less Sb appearing in the Ag-doped powder sample of Mg3.5-xAgxSb2 (x = 0.015) than the undoped Mg3.5Sb2 powder sample, indicating that Ag doping at the Mg sites can inhibit the appearance of the Sb phase to some extent. Our work implies that the emergence of the Sb phase is unlikely due to the decomposition of the Mg3Sb2 structure and can be hindered by reducing the Mg deficiency or Ag doping on the Mg sites.

Mesoporous Structure With Interconnecting Nanofibers by Irradiating Low Energy (∼100 keV) Ar+-ions on Gallium Antimonide Epi-Layer

Mesoporous structures with interconnecting nano-fibers (MSINs) are realized by irradiating low energy (50, 75, and 100 keV) beams of Ar + -ions normal to the surface of molecular beam epitaxially grown gallium antimonide (GaSb) epi-layer deposited on (100) oriented semi-insulating gallium arsenide (GaAs) substrates. The irradiation of 100 keV Ar + -ion beam at fluence of 1 × 10 17 ions/cm 2 provides optimal MSIN structure with distinct nanofibrous network. A physical model for evolution of MSINs with irradiation of energetic Ar + -ions at different fluences onto GaSb surface is illustrated as creation of point defects in the form of vacancy and interstitial sites. The ion tracking simulation using the Stopping and Range of Ions in Matter and Transport of Ions in Matter (SRIM-TRIM-2013) software resembles the formation of MSINs with Ar + -ion irradiation on GaSb epi-layer. The electron-microscopic, spectroscopic, and crystallographic analysis of the MSINs suggest the presence of nanocrystallites, high degree of oxidation, co-existence of gallium oxide (Ga 2 O 3 ) and antimony oxide (Sb 2 O 3 , Sb 2 O 5 ), and presence of elemental antimony (Sb) phase in the nanofiber interconnects.

Magnesium silicide-derived porous Sb-Si-C composite for stable lithium storage

Porous Sb-Si-C composite materials were synthesized through two-step high-energy mechanical milling (HEMM) and chemical etching processes as an anode material for lithium secondary batteries. Sb2O3 and Mg2Si as starting materials were transformed into Sb, Si, and MgO phases after the first step of HEMM. Activated carbon was then incorporated into the composites during the second step of the milling. Finally, porous composites were synthesized by removing MgO through chemical etching. The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, electron microscopy, and Brunauer–Emmett–Teller (BET) surface area measurement. The electrochemical lithiation and delithiation mechanism of the porous Sb-Si-C nanocomposite electrode was examined by using ex situ XRD analysis. Electrochemical test results demonstrated that the reversible capacity of approximately 450 mAh g−1 was maintained well after 200 cycles. This performance can be attributed to the porous structure and the amorphous carbon matrix for alleviation of volume changes during repeated Li+ insertion and extraction cycling.