Ti Sb Research Articles

Development of Sb2Se3 alloys by Ti-doping with ultralow resistance drift and improved microstructure for nonvolatile memory applications

The Sb2Se3 and Ti-doped Sb2Se3 phase change thin films were prepared by magnetron sputtering. The relationship between resistance drift and crystallization behavior of Sb2Se3 and Ti-doped Sb2Se3 thin films were thoroughly investigated. The results revealed that when Ti-doping concentration reaches 5.4 at. %, Ti5.4(Sb2Se3)95.4 thin film exhibited a high thermal stability with crystallization temperature of 225 °C and 10-year data retention temperature of 129.5 °C. This benefits to lower resistance drift coefficient from 0.067 for Sb2Se3 to 0.002 for Ti5.4(Sb2Se3)95.4. Further microstructural analysis revealed the suppression of large grain growth in Ti-doped Sb2Se3 thin films, while the formation of Ti–Sb and Ti–Se bonds being responsible for enhanced stability of the amorphous Ti-doped thin films. Moreover, the Ti doping promoted one-dimensional growth-dominated crystallization mechanism of the studied alloys, leading to the reduced nucleation index compared to Sb2Se3. The present study sheds valuable light on the effectively reducing nucleation randomness in chalcogenide-based phase-change materials.

Enhanced Thermoelectric Properties of Nb-Doped Ti(FeCoNi)Sb Pseudo-Ternary Half-Heusler Alloys Prepared Using the Microwave Method.

Pseudo-ternary half-Heusler thermoelectric materials, which are formed by filling the B sites of traditional ternary half-Heusler thermoelectric materials of ABX with equal atomic proportions of various elements, have attracted more and more attention due to their lower intrinsic lattice thermal conductivity. High-purity and relatively dense Ti1-xNbx(FeCoNi)Sb (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1) alloys were prepared via microwave synthesis combined with rapid hot-pressing sintering, and their thermoelectric properties are investigated in this work. The Seebeck coefficient was markedly increased via Nb substitution at Ti sites, which resulted in the optimized power factor of 1.45 μWcm-1K-2 for n-type Ti0.93Nb0.07(FeCoNi)Sb at 750 K. In addition, the lattice thermal conductivity was largely decreased due to the increase in phonon scattering caused by point defects, mass fluctuation and strain fluctuation introduced by Nb-doping. At 750 K, the lattice thermal conductivity of Ti0.97Nb0.03(FeCoNi)Sb is 2.37 Wm-1K-1, which is 55% and 23% lower than that of TiCoSb and Ti(FeCoNi)Sb, respectively. Compared with TiCoSb, the ZT of the Ti1-xNbx(FeCoNi)Sb samples were significantly increased. The average ZT values of the Nb-doped pseudo-ternary half-Heusler samples were dozens of times that of the TiCoSb prepared using the same process.

Fe segregation as a tool to enhance electrical conductivity of grain boundaries in Ti(Co,Fe)Sb half Heusler thermoelectrics

Fe segregation as a tool to enhance electrical conductivity of grain boundaries in Ti(Co,Fe)Sb half Heusler thermoelectrics

Alloyed triple half-Heuslers: a route toward high-performance thermoelectrics with intrinsically low lattice thermal conductivity

Alloyed triple half-Heusler Ti(Fe0.5+xCo0.25Cu0.25−x)Sb with intrinsically low thermal conductivity have been successfully designed and synthesized based on a valence balanced strategy.

Entropy engineering: A simple route to both p- and n-type thermoelectrics from the same parent material

Ternary half-Heusler (HH) semiconductors have been identified as excellent high-temperature thermoelectric (TE) materials, but the high thermal conductivity restricts the development and application. In this work, we report the design of the HH alloy Ti(Fe/Co/Ni)Sb with both p-type and n-type conductions from the same parent compound TiCoSb by entropy engineering. High-throughput (HTP) experiments have been first conducted to verify the formation of Ti(Fe1/3+xCo1/3Ni1/3-x)Sb solid solution and screen the range of compositions with the best p-type and n-type thermoelectric properties by regulating the Fe/Ni ratio. The random mixing of Fe/Co/Ni on the 4c site of the HH lattice induces a large lattice distortion, leading to a significantly reduced lattice thermal conductivity. Adjusting the sample composition (Fe/Ni ratio) changes the carrier concentration, carrier type and electronic band structure simultaneously, contributing to improved TE power factors for both p- and n-type materials. As a result, a peak TE figure of merit zT of up to ∼0.56 for p-type and ∼0.49 for n-type are achieved. Our experimental results demonstrate that entropy engineering is a promising strategy to extend the composition range and tune the TE properties for HH materials, which might be a generally applicable route to improve the thermoelectric performance of other TE materials.

Ab initio расчет зонной структуры и свойств модификаций соединения Ti-=SUB=-3-=/SUB=-Sb, допированного литием

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2×2×2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a = 5.217 Å) and tetragonal system (D8_m type structure; а = 10.457 Å, с = 5.258 Å). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8_mTi3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti–Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8_m) of Ti3Sb near the Fermi level for s, p, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8_m) increase the magnetic moment (M) as compared to the value of M (M_tot = 0.08 μ_B) of a “pure” Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb–Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb–Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti–Sb–Li system has been established. The isothermal section of the Ti–Sb–Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (<6.25 at. % Li) into the Ti3Sb (Space group Pm3 ̅n; № 223; a = 5.217 Å) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb–Li supercell.

Stable Positive Current Collectors for Li||Sb–Sn Liquid Metal Batteries

The corrosion of a liquid Sb–Sn alloy on a positive current collector (PCC) can seriously affect the performance of Li||Sb–Sn liquid metal batteries (LMBs) and hinder their industrial applications. This work systematically investigated Ti, Mo, and W as the PCCs of Li||Sb–Sn LMBs corrosion behaviors and electrochemical properties. The corrosion mechanism and cell performance recession reason are illuminated based on compatibility analysis and electrochemical measurements. Ti and Mo are more easily dissolved in the liquid Sb–Sn alloy than W, forming Ti–Sb–Sn and Mo–Sb–Sn corrosion products. The average corrosion rates of Ti, Mo, and W in the liquid Sb-Sn alloy are 0.105, 0.068, and 0.014 mm/a, respectively. These corrosion behaviors not only affect the cell voltage and capacity to varying degrees but also may cause potential security liability. Hence, W is an admirably stable PCC of Li||Sb–Sn LMBs, which can also serve as an electroconductive and corrosion-resistant protective coating to reduce cost and solve the forming problem.

Fast and scalable phase change materials Ti–Sb–Te deposited by plasma-enhanced atomic layer deposition

Current features of phase change memory (PCM) based on Ge2Sb2Te5 (GST) as a non-volatile memory is insufficient to meet the needs of storage class memory (SCM) such as extremely high-density, ultra-fast operating speed and long life cycle. In this study, Ti0.28Sb2Te3 (TST) device was fabricated based on atomic layer deposition (ALD) method and used as a phase change material. Due to the fast crystallization and low melting temperature of TST, the set speed can be reduced to 6 ns while the reset voltage can be decreased by 20% compared with GST-based device with the same cell structure. In addition, the ALD-deposited TST alloy showed a good gap-fill capability. These results indicate that the ALD-deposited TST film is a fast and scalable phase-change material applied to SCM.

Physical, electronic and thermoelectric properties of [001] surfaces of TiCoSb half-Heusler compound

The electronic and thermoelectric properties of [001] surfaces of half-Heusler compound TiCoSb are investigated consistently by combining first principles electronic structure calculations and BOLTZRAP transport theory. It was found that semi-metallic behavior in the Fermi level in comparison with bulk state of compound, is declined and just at Ti–Sb termination in minority spin state there is a gap near Fermi surface. Our calculations show that Ti–Sb termination has a high density near the Fermi level which is most due to d orbitals of Co atoms. It was found that p-type terminations have higher thermopower comparing with n-type terminations. Since the power factor and figure of Merit depend on electrical conductivity, the definitive factor in determining thermoelectric performance of a material is its thermal conductivity, which according to the calculations we performed, the lowest thermal conductivity has associated with Co–Sb terminations in majority spin state, therefore the most figure of Merit is related to this termination which is equal to 0.56. Phase diagram calculations were performed for [001] surfaces TiCoSb compound and stability of all terminations was investigated.

Interaction of the Components in the {Ce, Gd}-{Ti, Zr}-Sb Systems

The phase equilibria in the ternary systems {Ce, Gd}–{Ti, Zr}–Sb were investigated by means of X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The isothermal sections of the phase diagrams at 600°C were constructed. The formation of three ternary compounds (Ce2Ti7Sb12, Ce3TiSb5, and Gd2Ti11Sb14) was confirmed in the {Ce, Gd}–Ti–Sb systems and no more ternaries were found. The investigation of the {Ce, Gd}–Zr–Sb systems revealed several new ternary compounds and confirmed the known ones. The crystal structure of the new compound Ce0.08(3)Zr1.92(3)Sb was determined from X-ray powder diffraction data. The other new compounds in the Ce–Zr–Sb system were found to have compositions close to ~CeZrSb4and ~Ce2Zr3Sb5. In the Gd–Zr–Sb system the existence of a large homogeneity range was established for the GdZrSb compound along the isoconcentrate 33.3 at.% Sb: Gd1-xZr1+xSb (x= 00.905(18) at 600°C), and a new compound, ~Gd3Zr3Sb14, was discovered. The crystal structures at the boundary compositions of the Gd1-xZr1+xSb phase were refined from X-ray powder diffraction data.

Effect of Ti additions on structure and phase stability of Sb2Te3 thin films by experimental and theoretical methods

Influence of Ti additions in Sb2Te3 thin films on structure and phase stability was studied by experiments together with theoretical calculations. The incorporation of Ti atoms in the Sb2Te3 thin films caused formation of finer grains. By X-ray photoelectron spectroscopy and ab initio calculation, both the Sb and Te atoms are likely to be replaced by the Ti atoms to form Ti–Sb and Ti–Te covalent bonds. It suggests that the Ti atoms locate in Te1 position and interstice of the lattice.

Phase equilibria in the Ce–Ti–Sb and Gd–Ti–Sb ternary systems at 600°C and the crystal structures of the Ce2Ti7Sb12 and Gd2Ti11Sb14 compounds

Phase equilibria in the Ce–Ti–Sb and Gd–Ti–Sb ternary systems at 600°C and the crystal structures of the Ce2Ti7Sb12 and Gd2Ti11Sb14 compounds

Properties of Ti–Sb–Te doped with SbSe alloy for application in nonvolatile phase change memory

Sb2Se3 alloy is used as a dopant for Ti–Sb–Te phase change material aiming to improve the thermal stability of Ti–Sb–Te based phase change memory cell. In this paper, the thermal and electrical properties of Sb2Se3-doped Ti0.32Sb2Te3 are respectively investigated. Compared with Ti0.32Sb2Te3 material, (Sb2Se3)0.28(Ti0.32Sb2Te3)0.72 has better thermal stability with crystallization temperature of 203 °C and estimated 10-year data retention of 102 °C. For the (Sb2Se3)0.28(Ti0.32Sb2Te3)0.72-based PCM cell, it inherits the advantage of fast switching speed and good endurance of TST based one with wider SET/RESET window. The effects of Sb2Se3 doping on the structure of Ti0.32Sb2Te3 are also systemically studied. In crystalline (Sb2Se3)0.28(Ti0.32Sb2Te3)0.72 film structure, Se is prone to substitute Te and bond with Sb and Te in the Sb2Te3 lattice structure which may decrease the crystal lattice constant.

Performance improvement in a Ti–Sb–Te phase change material by GaSb doping

Herein, the GaSb-doped Ti0.09Sb0.38Te0.53(TST) material is investigated and considered to be a potential candidate for phase change random access memory (PCM) application due to its overall good performance. With a high crystallization temperature of 220 °C, (GaSb)0.11(Ti0.09Sb0.38T0.53)0.89 ((GaSb)0.11TST) exhibits a data retention of 10 y at 136.8 °C, which is much better than that of Ge2Sb2Te5 as well as TST. For the (GaSb)0.11TST-based cell, an electric pulse as short as 5 ns can fulfill the SET operation, thus demonstrating an extremely rapid crystallization speed. Furthermore, the cell shows a significantly lower power consumption for SET/RESET reversible switching than that of the Ge2Sb2Te5-based cell. The programming cycles can reach 1 × 104 cycles with stability resistance of about a two orders of magnitude on/off ratio.

Direct observation of titanium-centered octahedra in titanium-antimony-tellurium phase-change material.

Phase-change memory based on Ti0.4Sb2Te3 material has one order of magnitude faster Set speed and as low as one-fifth of the Reset energy compared with the conventional Ge2Sb2Te5 based device. However, the phase-transition mechanism of the Ti0.4Sb2Te3 material remains inconclusive due to the lack of direct experimental evidence. Here we report a direct atom-by-atom chemical identification of titanium-centered octahedra in crystalline Ti0.4Sb2Te3 material with a state-of-the-art atomic mapping technology. Further, by using soft X-ray absorption spectroscopy and density function theory simulations, we identify in amorphous Ti0.4Sb2Te3 the titanium atoms preferably maintain the octahedral configuration. Our work may pave the way to more thorough understanding and tailoring of the nature of the Ti–Sb–Te material, for promoting the development of dynamic random access memory-like phase-change memory as an emerging storage-class memory to reform current memory hierarchy.

Recent progress in calculations of electronic and transport properties of disordered thermoelectric materials

Results of electronic structure calculations in disordered thermoelectric materials are presented using KKR–CPA technique. Firstly, it is applied to detect the resonant impurities in selected materials, including PbTe, where Bloch spectral functions are computed. Secondly, in combination with the Boltzmann transport theory, we discuss the effect of band convergence in Mg2(Si–Sn) and band alignment in half-Heusler Ti(Co–Fe–Ni)Sb, on thermoelectric performance. Moreover, the influence of spin–orbit interaction on band features and thermopower is shown in Mg2X (X = Si, Ge, Sn) compounds.

Ti–Sb–Te Alloy: A Candidate for Fast and Long-Life Phase-Change Memory

Phase-change memory (PCM) has great potential for numerous attractive applications on the premise of its high-device performances, which still need to be improved by employing a material with good overall phase-change properties. In respect to fast speed and high endurance, the Ti-Sb-Te alloy seems to be a promising candidate. Here, Ti-doped Sb2Te3 (TST) materials with different Ti concentrations have been systematically studied with the goal of finding the most suitable composition for PCM applications. The thermal stability of TST is improved dramatically with increasing Ti content. The small density change of T0.32Sb2Te3 (2.24%), further reduced to 1.37% for T0.56Sb2Te3, would greatly avoid the voids generated at phase-change layer/electrode interface in a PCM device. Meanwhile, the exponentially diminished grain size (from ∼200 nm to ∼12 nm), resulting from doping more and more Ti, enhances the adhesion between phase-change film and substrate. Tests of TST-based PCM cells have demonstrated a fast switching rate of ∼10 ns. Furthermore, because of the lower thermal conductivities of TST materials, compared with Sb2Te3-based PCM cells, T0.32Sb2Te3-based ones exhibit lower required pulse voltages for Reset operation, which largely decreases by ∼50% for T0.43Sb2Te3-based ones. Nevertheless, the operation voltages for T0.56Sb2Te3-based cells dramatically increase, which may be due to the phase separation after doping excessive Ti. Finally, considering the decreased resistance ratio, TixSb2Te3 alloy with x around 0.43 is proved to be a highly promising candidate for fast and long-life PCM applications.

Single spin channels in Fe-doped CoTiSb semiconductor

The Fe-based single atomic chains are designed in the semiconductive CoTiSb matrix by continuously substituting Fe for Ti, Ti–Sb or Co in [001] crystallographic direction. The electronic structures and magnetic properties of CoTiSb supercells with the Fe-based single atomic chains have been investigated using the first-principles calculations. We predict that the single atomic chains of Fe–Sb (achieved by substituting Fe for Ti) and Fe-vacancy (achieved by substituting Fe for Co) show a 100% spin polarization and form a very small single spin channel. The single atomic chains of Fe–Fe (achieved by substituting Fe for Ti and Sb) show a spin-gapless characteristic.

SnSb–TiC–C nanocomposite alloy anodes for lithium-ion batteries

SnSb–TiC–C nanocomposite alloy anodes for lithium-ion batteries have been synthesized by a mechanochemical process involving high-energy mechanical milling of Ti–Sn and Ti–Sb precursors with carbon black. Characterization of the formed nanocomposites using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals that these alloys are composed of crystalline nanoparticles of SnSb dispersed in a matrix of crystalline TiC and amorphous carbon. The SnSb–TiC–C alloy shows an initial gravimetric capacity of 769 mAh g−1 (1385 mAh cm−3), an initial coulombic efficiency of 84.9%, and a tap density of 1.8 g cm−3. The buffer matrix of TiC and carbon in the nanocomposite alloy anodes accommodates the large volume change occurring during the charge–discharge process and leads to enhanced cyclability compared to pure SnSb anodes as well as previously published SnSb composites.

Understanding the crystallization behavior of as-deposited Ti–Sb–Te alloys through real-time radial distribution functions

Phase change materials, successfully used in optical data-storage and non-volatile electronic memory, are well-known for their ultrafast crystallization speed. However, the fundamental understanding of their crystallization behavior, especially the nucleation process, is limited by present experimental techniques. Here, real-time radial distribution functions (RDFs), derived from the selected area electron diffractions, are employed as structural probes to comprehensively study both nucleation and subsequent growth stages of Ti-doped Sb2Te3 (TST) materials in the electron-irradiation crystallization process. It can be found that the incorporation of Ti atoms in Sb2Te3 forms wrong bonds such as Ti-Te, Ti-Sb, breaks the originally ordered atomic arrangement and diminishes the initial nucleus size of the as-deposited films, which results in better thermal stability. But these nuclei hardly grow until their sizes exceed a critical value, and then a rapid growth period starts. This means that an extended nucleation time is required to form the supercritical nuclei of TST alloys with higher concentration. Also, the increasing formation of four-membered rings, which served as nucleation sites, after doping excessive Ti is responsible for the change of the crystallization behavior from growth-dominated to nucleation-dominated.