Transition Metal Hf Research Articles

Theoretical insight of confinement of filament in SrMoO3 electrode by compositional control for memory devices

This study comprehensively examined the structural, dynamical, electronic, and optical characteristics of SrMoO3 as an electrode material for the confining conducting filament in resistive random access memory (RRAM). This study is novel in that it examines the compositional control and interaction between extrinsic defects (dopants) and intrinsic defects (oxygen vacancies) acting as a transition driving force in thermodynamically stable composites for a resistive switching mechanism. In the absence of oxygen vacancies (Vos), relatively strong, confined metal-cation-based filaments formed around the dopant proved that extrinsic defects caused by substitutional dopants replacing Mo atoms are more efficient at producing low-resistance states in SrMoO3 than intrinsic defects. Filaments of the order of a few Ås around the defect site will help to solve the uniformity and scaling problems associated with resistive switching. This finding further supported the usefulness of noise (in this case, a dopant or Vos is the source of an external or internal perturbation). The optical conductivity produced in response to incident photons in the infrared energy range also verified the suitability of doped SrMoO3 systems for optoelectronic RRAM synaptic devices. This study's potential energy lineup-based dopant selection rule suggested that substitutional doping using the heavy transition metal Hf as an acceptor dopant yields relatively excellent results for applications involving low-power SrMoO3-based RRAM synaptic devices.

Systematics of the Third Row Transition Metal Melting: The HCP Metals Rhenium and Osmium

The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain its phase diagram. Our results indicate that Re, which generally assumes a hexagonal close-packed (hcp) structure, melts from a face-centered cubic (fcc) structure in the pressure range 20–240 GPa. We conclude that the recent DAC data on Re to 50 GPa in fact encompass both the true melting curve and the low-slope hcp-fcc phase boundary above a triple point at (20 GPa, 4240 K). A linear fit to the Re diamond anvil cell (DAC) data then results in a slope that is 2.3 times smaller than that of the actual melting curve. The phase diagram of Re is topologically equivalent to that of Pt calculated by us earlier on. Regularities in the melting curves of Re, Os, and five other 3rd-row transition metals (Ta, W, Ir, Pt, Au) form the 3rd-row transition metal melting systematics. We demonstrate how this systematics can be used to estimate the currently unknown melting curve of the eighth 3rd-row transition metal Hf.

First-Principles Study in New Hf2CoZ (Z = B, C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) Heusler Alloys

The full-potential linearized augmented plane wave method within density functional theory was used to investigate the electronic structures, magnetic properties, and half-metallicity in Hf2CoZ (Z = B,C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) alloys with AlCu2Mn- and CuHg2Ti-type structures. The AlCu2Mn-type structure is energetically favorable than the CuHg2Ti-type structure for all compounds. Hf2CoGa, Hf2CoAl, Hf2CoIn, Hf2CoTl, and Hf2CoSn compounds in the CuHg2Ti-type structure were half-metallic ferromagnets. The d-d and covalent hybridizations between transition metals Hf and Co were effective in the formation of minority band gap. The total magnetic moments of half-metallic Hf2CoZ (Z = Al, Ga, In, Sn, and Tl) compounds in the CuHg2Ti-type structure obeyed the Slater–Pauling rule (M tot = Z tot − 18). Hf2CoIn and Hf2CoTl compounds were half-metals in relatively wide ranges of lattice constants which indicates that they can be promising and interesting candidates for spintronic devices.

Ab initio investigation into the structural, electronic and elastic properties of AlCu2TM (TM = Ti, Zr and Hf) ternary compounds

The Al–Cu–TM (TM = transition metal) alloy system has attracted great attention for both excellent glass-forming ability and its interesting physical properties. In this work, an investigation into the crystal, electrical and elastic properties of the AlCu2TM (TM = Ti, Zr, and Hf) compounds has been conducted by first-principles calculations based on density-functional theory. The fully relaxed structure parameters of the AlCu2TM compounds are in good agreement with previous experimental and other theoretical results. Besides, the cohesive energies of all the AlCu2TM compounds have been evaluated. The energy band and densities of state of these compounds are also obtained. According to the calculated single crystal elastic constants, all the compounds are mechanically stable. The polycrystalline bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio have been deduced by using Voigt–Reuss–Hill (VRH) approximations. The calculated negative Cauchy pressure and ratio of bulk modulus to shear modulus indicated that the AlCu2TM compounds are ductile materials. The Debye temperatures of the AlCu2TM compounds decrease with increasing the TM (Ti, Zr, and Hf) atomic number.

Adsorption of Al, O, Hf, Y, Pt, and S Atoms on α-Al2O3(0001)

We use first-principles density functional theory to investigate adsorption of Al, O, Hf, Y, Pt, and S-atoms on the α-Al2O3(0001) surface. We identify stable adsorption sites and predict binding energies and structures. We find that Al, Hf, and Y preferentially adsorb on threefold-hollow sites, transfer electrons to the surface, and form ionic bonds to the three oxygen atoms. In contrast, the most stable adsorption site for Pt and S is ontop an oxygen atom, and we do not observe significant charge transfer. We find a binding order of S < Pt < O < Al ≪ Y < Hf, which reflects both the ease with which the early transition metals Hf and Y ionize, as well as the (nearly) closed-shell repulsions influencing the adsorption of O, Pt, and S. We use these results to rationalize some observations regarding the stability of thermal barrier coatings.

A deep-level transient spectroscopy study of transition metals in n-type germanium

The deep-level parameters of a number of technological relevant transition metals—Hf, Ti, Cr, Fe, Co and Ni—in n-type germanium have been studied by deep-level transient spectroscopy (DLTS). The metals have been introduced by ion implantation followed by annealing at 500 °C for 5 min. In most cases the annealing treatment is sufficient to remove the implantation point defects from the substrate, leaving only metal-related electron traps in the spectra. From the fact that for each metal, one (or more) peaks at a different position and with a different activation energy is observed, it is concluded that levels specific for the individual metals have been detected. This is further validated by the observation that the corresponding trap concentration increases with the implantation dose. In some cases, e.g. Hf, we believe that it is the first observation of the impurity-related deep electron traps in germanium.

Saturated solid-solution hardening behavior of Ir–Hf–Nb refractory superalloys for ultra-high temperature applications

The principles of multi-component alloying and saturated solid-solution hardening were combined for the design and development of Ir-based alloys for ultra-high temperature applications. It is found that as a solute, the transition metal Hf combined with Nb exerts its full potential for solid-solution hardening on the solvent Ir at room temperature and higher. With a monolithic saturated face-centered cubic structure, the Ir–3Hf–5Nb alloy has a 0.2% yield strength of as high as 140 MPa even at 1950 °C.

Incorporation of the transition metal Hf into GaN

The perturbed angular correlation (PAC) technique was applied to study the incorporation of the transition metal Hf into GaN after implantation. To this end the PAC probe 181Hf(181Ta) was implanted into epitaxial Wurtzite GaN layers (1.3 μm on sapphire) with an energy of 160 keV and doses of 7× 1012 at/cm2. PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in the 300–1000oC temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency (QIF) of νQ= 340 MHz for 30% of the probe nuclei. Annealing up to 600oC reduces the damping of this frequency without an increase of the probe atom fraction fs in these sites. Above 600oC fs grows rapidly until after the 900oC RTA step more than 80% of the Hf probes experience a well defined QIF due to the incorporation of Hf on undisturbed sites of the hexagonal GaN wurtzite lattice. An interaction frequency of νQ= 340 MHz is derived. RTA and furnace annealing yield similar results for annealing up to 800oC, where the undisturbed fraction reaches about 60%. Then RTA at higher temperatures increases this fraction, while furnace annealing leads to a decrease down to 22% after annealing at 1000oC. To our knowledge this is the first time that a transition metal probe like Hf is incorporated to such a large extent into a semiconductor lattice.

Hf&lt;sub&gt;2&lt;/sub&gt;Ni Compound Investigation: Electronic Structure and Electric Field Gradient

The electronic structure of the Hf2Ni intermetallic compound has been obtained using the first-principle full-potential (FP) linear-muffin- tin-orbital (LMTO) method in the atomicsphere approximation (ASA). The electric field gradient (EFG) tensor is calculated for both HI' and Ni sites and compared with the experiment. The theoretical results show that the EFG is determined dominantly by the p electrons. 1. Introd uction The interaction between the nuclear quadrupole moment and the electric field gradient (EFG) at the atomic site with noncubic point symmetry can be determined by various hyperfine interaction measurements, such as: perturbed angular correlation (PAC), perturbed angular distribution, and nuclear magnetic resonance (NMR). These methods were used widely to get information about surfaces, impurities, and vacancy related defects. A lot of experimental investigations of EFG in complex compounds with many atoms per primitive cell have appeared in recent years. Some of them have been devoted to the timedifferential perturbed angular correlation (TDPAC) measurements of nuclear quadrupole interactions in the ordered intermetalic compounds of transition metal Hf. It was shown that EFG reveals interesting properties in these compounds. These compounds represent a challenge for the theory due to their complexity. The explanation of the origin and the magnitude of EFG in one of them, e.g. Hf2Ni, is the subject of the present theoretical investigation.

Cohesion and lattice stabilities in the 5d transition metals: Full versus muffin-tin potentials.

First-principles linear augmented-Slater-type-orbital (LASTO) calculations have been carried out for the 5d transition metals Hf through Au. Among the various topics discussed are the stability of the hcp, fcc, and bcc phases, lattice volumes, and cohesion. Effects of the full versus the muffin-tin potential are also examined; in particular the ground state of Au is now correctly predicted to be fcc with use of the full potential. The hcp-fcc energy differences are a factor of 5 smaller than the corresponding fcc-bcc energy differences along the row.