The Electric Field Gradients in (Zr/Hf)Al3 and (Zr/Hf)2Al3 Intermetallic Compounds Studied by 181Ta- and 111Cd-PAC Spectroscopy

The electric quadrupole hyperfine interactions for ¹⁸¹Hf/¹⁸¹Ta and for ¹¹¹In/¹¹¹Cd probes in polycrystalline ZrAl₃ and Zr₂Al₃ compounds were measured in the temperature range 30–1100 K and compared with the results for isostructural hafnium aluminides. On the basis of the similarities of the numbers, sizes and asymmetries of electric field gradients, lattice site allocations were made. In all matrices, ¹⁸¹Hf/¹⁸¹Ta was found to substitute the Hf/Zr site. The ¹¹¹In/¹¹¹Cd impurities were also assigned to the Hf/Zr site in the compounds (Zr/Hf)Al₃, but appear to substitute the two non-equivalent Al sites in the Zr₂Al₃ and Hf₂Al₃ phases. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hf3Al2 and Zr3Al2 Isostructural Aluminides Studied by PAC with 181Ta and 111Cd Probes

The electric quadrupole hyperfine interactions for ¹⁸¹Hf/¹⁸¹Ta and for ¹¹¹In/¹¹¹Cd probes in polycrystalline Zr₃Al₂ and Hf₃Al₂ compounds were measured in the temperature range 24–1100 K. The hyperfine quadrupole interaction parameters were determined after different doping techniques and heat treatments of the samples.¹⁸¹Hf/¹⁸¹Ta was found to substitute the Hf/Zr sites and the ¹¹¹In/¹¹¹Cd impurities appear to substitute both the 8(j) Al sites and the three nonequivalent Hf/Zr sites.     

Zr-induced structural changes in Hf1−x Zr x O2 high-k thin films

The local symmetries around the Hf sites in thin films of Hf_1?x Zr _x O₂/Si(100) were probed using grazing incidence extended X-ray absorption fine-structure spectroscopy (EXAFS). The effects of the Zr incorporation on the local crystal symmetries were investigated using Hf L₃ EXAFS at the Beamline X23A2 of the Brookhaven National Laboratory. The Zr ratios in the various films were set to between 0.0 and 1.0. Significant changes in the local environment were observed for x = 0.25 or greater values. For x = 0.0, the film local structure around Hf sites remain in the equilibrium monoclinic phase as referenced from our previous studies on HfO₂ thin films on Si(100). When Zr is introduced, tetragonal symmetry around the Hf atom appears and becomes dominant at x = 0.63. Using the EXAFS theoretical simulations and non-linear least-square fit results, the fractions of the monoclinic versus tetragonal phases were identified in each film.     

Nb对C-15结构V2(HfZr)系列的超导转变温度的影响

本文中研究了C-15结构V₂Hf_1-xNb_x,V₂Zr_1-xNb_x和V₂Hf_0.5Zr_0.5-xNb_x系列的超导转变温度T_c与Nb合量x的关系,发现V₂Zr,V₂Hf加Nb后与V₂Hf_0.5Zr_0.5加Nb后性能显著不同。测定了V₂Zr,V₂Hf和V₂Hf_0.5Zr_0.5的X射线光电子能谱。结果表明,当Hf原子和Zr原子共存于AB₂化合物的A位上时,发生了一种增强原子间相互作用的新的电荷转移。这个事实支持由角动量分波表象能带论方法分析电声耦合超导原理的结果对四元V₂(HfZrNb)系列的超导行为提出的一种可能解释:4d-5d原子配位可能有助于提高4d导带的杂化程度,从而有利于提高超导T_c。 关键词：     

Ti1－x(Hf0.919Zr0.081)xNiSn的制备及热电性能

采用固相反应法合成了单相的Ti_1-x(Hf_0.919Zr_0.081) _xNiSn (x＝0.00—0.15)，并用放电等离子烧结方法制备出密实块体材料. 研究 了Hf和Zr同时在Ti位上的等电子合金化对Ti基半Heusler化合物热电性能的影响规律. 结果 表明：少量的Hf和微量的Zr在Ti位上的等电子合金化，显著地降低了体系的热导率κ，同时 显著地提高了体系的Seebeck系数α. 组成为Ti_{0.85关键词： 半Heusler 固相反应 热电性能}     

Ta对C—15相V2Hf和V2(Zr0.5Hf0.5)系列声子性能的影响

本文用中子飞行时间方法对C-15相的超导材料V₂Hf,V₂Ta和V₂Hf_0.8Ta_0.2以及V₂Zr_0.5。Hf_0.5和V₂Zr_0.5Hf_0.33Ta_0.17的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V₂Zr和V₂(Hf_0.5Zr_0.5)系列声子性能的影响一致:声子频率随超导转变温度T_c增加而软化,随T_c减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高T_c起了作用。结果还进一步表明V₂Zr或V₂Hf与V₂(Zr_0.5Hf_0.5)之间有着质的差别,V₂Hf加Ta后,T_c增加,声子频率软化,而V₂(Zr_0.5Hf_0.5)加Ta后,T_c减小,声子频率则略有硬化。这与V₂Zr和V₂(Hf_0.5Zr_0.5)加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。 关键词：     

Electric field gradients at Ta in Zr and Hf inter-metallic compounds

Here we calculate the electric field gradient (EFG) at the nucleus of the substitutional Ta impurity site in Zr₂T and Hf₂T (T=Cu, Ag, Au, and Pd) C11_b inter-metallic compounds. We use the ab initio FP-LAPW method as embodied in the Wien97 code in a super-cell approach and include lattice relaxations around the impurity. Our results are compared with EFG values inferred from measurements of the quadrupole coupling constants at the ¹¹¹Ta probe in these compounds performed with the time differential perturbed angular correlation (TDPAC) technique. We also performed EFG calculations for the pure inter-metallic compounds. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Ta probe in the TDPAC measurements of Hf and Zr compounds. Our results show that, although the EFGs at the Hf site are very similar to the EFGs at the Ta impurity, there is no direct correlation between the Zr and Ta EFGs.     

The first principle study of magnetic properties of Mn2WSn,Fe2YSn (Y=Ti,V), Co2YSn (Y=Ti,Zr, Hf,V, Mn) and Ni2YSn (Y=Ti,Zr, Hf,V, Mn) heusler alloys

The spin polarized electronic band structures, density of states (DOS) and magnetic properties of Mn₂WSn, Fe₂YSn (Y=Ti, V), Co₂YSn (Y=Ti, Zr, Hf, V, Mn) and Ni₂YSn (Y=Ti, Zr, Hf, V, Mn) huesler compounds are reported. The calculations are performed by using full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The magnetic trend in these compounds is studied using values of magnetic moments, exchange interaction and calculated band gap. The results reveal that Mn₂WSn and Ni₂VSn show 100% spin polarization, Co₂YSn (Y=Ti, Zr, Hf, Mn), Fe₂YSn (Y=Ti, V), and Ni₂MnSn exhibit metallic nature and Ni₂YSn (Y=Ti, Zr, Hf) and Co₂VSn show semi-conducting behavior.     

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript>

The microstructures of amorphous and polycrystalline ferroelectric Hf_0.5Zr_0.5O₂ films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO₂ and ZrO₂. After rapid thermal annealing, the mixed Hf_0.5Zr_0.5O₂ oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO₂ and ZrO₂. The presence of the HfO₂ and ZrO₂ phases in the Hf_0.5Zr_0.5O₂ films is also detected by ellipsometry.     

Reduced lattice thermal conductivity of Ti-site substituted transition metals Ti1-XTMXNiSn: A quasi-harmonic Debye model study

TiNiSn thermoelectric (TE) material has a high power factor, but it also has high thermal conductivity, which is a problem for low performance. In this work, we propose to reduce the lattice thermal conductivity (κ_lat) of the transition metal (TM) with substitution on the Ti-site TiNiSn as the model Ti_1–XTM_XNiSn (TM = Sc, Zr, Hf, V, Nb and Mn) by the quasi-harmonic Debye model calculation from 0 – 1000 K. The structural properties were investigated through the equation of state by a first-principles calculation. κ_lat was calculated by the Slack and Berman method using the Debye temperature (Θ) and Grüneisen parameter. The calculated results revealed that the structure increased with substitution by Sc, Zr, Hf, and Nb, but V and Mn exhibit a structure less than that of TiNiSn. The calculated Θ of TiNiSn is 404.86 K decreased with substitution by Sc, Zr, Hf, Nb, and Mn, and then slightly increased by V. The Sc, Zr, Hf, and Mn substitution significantly decreases the calculated κ_lat from 9.23 W m^–1 K^–1 (for TiNiSn) to 6.72 – 9.07 W m^–1 K^–1 at 300 K. Ti_0.75Zr_0.25NiSn, Ti_0.75Hf_0.25NiSn, and Ti_0.50Mn_0.50NiSn can reduce κ_lat by 27.19%, 20.26%, and 17.65%, respectively, which shows good potential for enhancing the κ_lat of TiNiSn.     

Effect of Substitution of Zr and Pr on magnetic properties of R2Co17(R=Er,Yb)

Magnetic properties (saturation magnetizations, Curie temperatures and anisotropy fields) have been measured for the ternary systems Er₂Co_17-xZr_x and Yb₂Co_17-xZr_x and for the quaternary system Er_2-yPr_yCo_16.4Zr_0.6. Introduction of Zr expands the lattice and diminishes the Curie temperature, both indicating Zr replaces Co. Saturation magnetization is diminished, when Zr replaces Co, more rapidly than simple dilution, suggesting Co d-band filling by electron transfer from Zr. The anisotropy field (H_A) is sharply increased when Co replaces Zr, indicating that both preferential substitution and band structure effects are involved. Replacement of Er by Pr enhances H_A, presumably because of preferential replacement of Er at the 2d site. H_A of 42 kOe (at 295 K) was achieved for Er_1.6Pr_0.4Co_16.4Zr_0.6.     

The influence of dibutyl phosphoric acid on zirconium extraction with diluted tributyl phosphate and the role of uranyl nitrate

Distribution coefficients of zirconium (D_Zr) in the 30% TBP — aqueous HNO₃ solution extraction system rise 1000–2000 times with the increase of the dibutyl phosphoric acid (HDBP) concentration from 0 to 0.01–0.08 mol/L. A solvate with the molar ratio Zr: HDBP=1 was found by IR spectroscopy and analytic methods in the initial range of HDBP concentration. In the presence of U(VI) D_Zr decreases with the growing U concentration, however, the ratio of Zr distribution coefficient in the presence of HDBP (D_AZr) to D_Zr determined in its absence, R_Zr=D_AZr/D_Zr, is rather high. Function of enhancement (F) was introduced for the evaluation of simultaneous influence of U and HDBP on Zr extraction. An increase of the U concentration resulted first in the decrease in F_Zr, and then in its increase. The rising part of the F_Zr curve was more noticeable at a molar excess of Zr over HDBP. The mechanism of Zr extraction by 30% TBP solution in the presence of HDBP when Zr is in excess to HDBP indicates the formation of the solvate with the ratio Zr: HDBP=1; in the presence of U(VI) the complex with the same ratio is formed by the HDBP interaction with U in the system with a great excess of both HDBP and Zr.     

Zr and Hf microalloying in an Al–Y–Fe amorphous alloy. Relation between local structure and glass-forming ability

The effects of the addition of small amounts of Zr and Hf (0.5–3%) on the atomic structure of Al₈₈Y₇Fe₅ metallic glass were examined from extended X-ray absorption fine structure (EXAFS) experiments to better understand the influence of these microadditions on the glass-forming ability of this alloy. Measurements at the Zr K and Hf LIII absorption edges allowed the local structures around Zr and Hf atoms to be determined. The same Al environment was found for the different concentrations, consisting of a small cluster extending up to 4.5 Å around the Zr atoms and up to 6 Å around the Hf ones. Although the clustering effect is smaller in the Zr neighbourhood, a drastic shortening of the nearest Zr–Al distance is shown, providing evidence for some covalent character to the bonding, in line with the increased glass-forming ability found in the alloys made with the Zr microaddition.     

Structures, chemical bonding, magnetisms of small Al-doped zirconium clusters

The geometrical and electronic properties of small Al-doped Zrn−1 and host Zrn clusters (n=2-8) are investigated with hybrid HF/DFT functional: B3LYP. For the most favorable configurations of Zrn−1Al clusters, the Al atom prefers to be located on the surface of host zirconium clusters. The isomers that correspond to low coordination number of Zr-Al bonds are found to be more stable. The doping of Al atom in Zrn−1 clusters improves the chemical activities of host clusters. The Zr₅, Zr₇, Zr₄Al and Zr₆Al clusters behave the stronger stabilities relative to their respective neighbors. The strong s-d hybridizations are presented in all bonding Zr atoms. The values of WBI together with AIM analysis suggest that the Zr-Zr interactions are stronger than those between Zr and Al atoms. The doping of Al atom results into the decrease of spin magnetic moments for host zirconium clusters. The moments are mainly derived from the 4d electrons of bonding Zr atoms.     

Interfacial properties of Ce<Subscript>0.75</Subscript>Zr<Subscript>0.25</Subscript>O<Subscript>2</Subscript> supported noble metals (Pd,Pt) from first principles

First-principles electronic structure calculations of noble metals (NM=Pd, Pt)/Ce_0.75Zr_0.25O₂ systems are presented. It is found that: the NM adatoms do not prefer to stay at the atop or the bridge sites of the cations (Ce and Zr), but prefer to be adsorbed at or around the anion sites. The most preferable adsorption sites for both the Pd and Pt adatoms are the O-bridge sites neighboring the Zr dopant. The Pt adatom show much stronger interaction with the Ce_0.75Zr_0.25O₂(111) surface than does the Pd adatom. The interactions of the NM/Ce_0.75Zr_0.25O₂(111) interfaces are stronger than those of the corresponding NM/ceria(111) interfaces. There are some metal induced gap states (MIGS) appeared in the gaps of the NM/Ce_0.75Zr_0.25O₂(111) interfaces, which are important to catalytic properties of the NM/Ce_0.75Zr_0.25O₂(111) catalysts.     

Effect of substitution of Zr on the magnetic properties of R2Co17 (R = Ce and Sm)

The ternary systems Ce₂Co_17?xZr_x and Sm₂Co_17?xZr_x have been studied to ascertain the effect of Zr substitution on the magnetic properties. X-ray diffraction experiments show that single phase materials can be obtained only in the range of x ≤ 1 and that Zr stabilizes the hexagonal Th₂Ni₁₇ structure. The unit cell volume is found to increase by substitution of Zr. The Curie temperature T_c decreases monotonically with increasing x at an approximate rate of 100 and 90 deg/atom for the Ce and Sm systems, respectively. The saturation magnetic moments also decrease monotonically with increasing x for both the systems. The rate of decrease is larger than that expected as a simple dilution. The anisotropy fields H_A are significantly increased by Zr substitutions for both the systems, reaching 70 and 200 kOe at 77 K in the cases of Ce₂Co₁₆Zr₁ and Sm₂Co₁₆Zr₁, respectively. Among all the substituents studied until now, Zr seems to be the most effective for permanent magnet applications. Crystallographic and magnetic characteristics indicate that Zr replaces Co when the ternaries are formed.     

Pac studies of ZrMn2+x alloys and their hydrides

¹⁸¹Ta PAC and electron diffraction experiments on ZrMn₂ show that the presence of Hf in substitution for Zr at a concentration of 2 at. % can be responsible for distortions from the C14 structure of this intermetallic alloy. The PAC spectra recorded between RT and 50K for the hydride Zr_0.98 Hf_0.02 Mn₂H_3.2 display two successive modifications in the temperature regions 180–150K and 100–50K. In the present state of PAC data analysis, we are not able to claim that such modifications are related to the low-temperature magnetic properties of ZrMn₂ hydrides.     

Crystal structure, electronic and elastic properties for novel Hf3AlN and Zr3AlN ceramics explored by first principles studies

Investigations into crystal structure, electronic and elastic properties of M₃AlN (M=Hf, Zr) had been conducted by plane-wave pseudopotential calculations. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of these two compounds. The charge density distributions and density of states indicate that there exist relatively soft Al-M and strong N-M covalent bonds, which might be contributed to layered chemical bonding character of M₃AlN. By analyzing Cauchy pressure and the bulk modulus to C₄₄ ratio, Hf₃AlN was predicted to be more ductile than Zr₃AlN.     

Hyperfine Interactions of 181Ta in Zr2Ni Observed Using PAC Spectroscopy

We have measured nuclear electric–quadrupole interactions (EQI) at ¹⁸¹Ta impurities substituted as Hf atoms into the Zr site in Zr₂Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200 K. Over the entire range of temperature, the Zr₂Ni crystal has a bct Al₂Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω₀=601(3) Mrad s⁻¹, and an asymmetry parameter η=0.835(2). At 1200 K, ω₀ decreases to 516(3) Mrad s⁻¹, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω₀ is consistent with a (1−BT ^3/2) power law, in which B=6×10⁻⁶ K^−3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples as prepared are remarkably free of strain and defects. These results indicate that the Zr₂Ni structure does not promote the formation of defects and that the power-law dependence of ω₀ on T is insensitive to the asymmetric nature of the crystal. This revised version was published online in September 2006 with corrections to the Cover Date.     

Chemical vapor deposition of ZrxTi1−xO2 and HfxTi1−xO2 thin films using the composite anhydrous nitrate precursors

Zr-Ti and Hf-Ti composite nitrates were successfully developed as single-source precursors for the chemical vapor deposition (CVD) of Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ thin films. The Zr-Ti nitrate can be assumed as a solid solution of the individual Zr and Ti nitrates, and the Zr/Ti molar ratio in the deposited Zr_xTi_1−xO₂ films is consistent with that in the precursor. The Hf-Ti nitrate appears to be a mixture of the Hf and Ti nitrates and the composition of the deposited Hf_xTi_1−xO₂ films depends remarkably on the heating time of precursor. Both Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films exhibit trade-off properties between band gap and dielectric constant. The obtained results suggest that Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films are promising candidates for gate dielectric application to improve the scalability and reduce the leakage current of the future complementary metal-oxide-semiconductor (CMOS) devices.