Spectroscopic studies of Ni2+ in calcium tartrate tetrahydrate

The optical absorption spectrum of a single crystal of calcium tartrate tetrahydrate, doped with Ni²⁺ ions, is investigated at laboratory and liquid nitrogen temperatures. From the analysis of the unpolarised and polarised spectra, the site symmetry of the Ni²⁺ ion is attributed to an elongated octahedron with a small tetragonal (C_4v) distortion.The analysis results in the following crystal field parametersB=875 cm^–1,C=3980 cm^–1,Dq=900 cm^–1, Dt=32cm^–1.The authors wish to express their thanks to the Head of the Department of Physics, I.I.T., Madras for providing the facilities to conduct experiments on a Cary-14 spectrophotometer. They wish to express their thanks to Prof. S.Radhakrishna (I.I.T., Madras) and Prof. S.V. J.Lakshman (S.V. University) for thier interest in the work. The authors are grateful to the U.G.C. (India) for financial assistance.     

The substitution of Fe2+ ions by Ni2+ ions in green rust one compounds

The oxidation of Fe(OH)₂ in the presence of Cl^– or CO ₃ ^2– ions leads, in the first stage of the reaction, to chloride-containing green rust one (GR1), 3Fe(OH)₂· Fe(OH)₂Cl·nH₂O, or carbonate-containing GR1, 4Fe(OH)₂·Fe₂(OH)₄CO₃·nH₂O, respectively. These GR1 compounds give the ferric oxyhydroxides by further oxidation. If a hydroxide Ni _x Fe_1–x (OH)₂ is initially precipitated, the reaction leads to a nickelous-ferric compound isomorphous to the ferrous-ferric GR1, but stable with respect to the oxidizing action of air. Similarly, the oxidation of a nickelous-ferrous hydroxide, in the presence of excess OH^– ions, leads to a nickelous-ferric GR1, a layered hydroxide with anionic interlayers made of OH^– ions and water molecules. The Mössbauer spectra of these nickelousferric GR1 display two ferric doublets, D₀ withIS=0.34 mm/s andQS=0.45 mm/s and D₁ withIS=0.36 mm/s andQS=0.86 mm/s. The existence of a ferrous-ferric GR1 incorporating OH^– ions, a compound never observed so far, is strongly suspected.     

Superconductivity induced phonon anomalies in the Raman spectra of Zn and Ni doped YBa2Cu3O7

Here we present Raman spectra of YBa₂(Cu_1–x Zn _x )₃O₇ and YBa₂(Cu_1–x Ni _x )₃O₇ as a function of temperature and Zn or Ni content. The temperature dependence of two modes at 340 and 440 cm^–1 is analyzed. Similarly to the infrared measurements it is found that Zn substantially suppresses the superconductivity induced phonon softening whereas, Ni does not affect much that effect. Moreover, the superconductivity induced phonon stiffening of the 440 cm^–1 mode completely disappeared with the Zn doping. We find this behaviour might support the model where Zn acts effectively as a magnetic pair breaker.     

Hydrogenation of Zr2Ni

The intermetallic compound Zr₂Ni has been found to take up hydrogen on charging at room temperature. Zr₂(NiFe) H_4.7 and Zr₂(NiFe) H_4.5 show the same structure (CuAl₂ type) as the uncharged compound but with an expanded lattice.Analysis of room temperature spectra in zero and applied fields indicates that the⁵⁷Fe atoms occupy Ni sites in Zr₂(Ni ⁵⁷Fe). Volume expansion effects account for about one third of the increase in isomer shift ( +0.58 mms^–1) observed on hydrogenation. The distribution of hydrogen atoms around the probe³⁷Fe atoms also causes a decrease of 0.23 mms^–1 in the mean value for the quadrupole splitting compared Rith uncharged Zr₂Ni.     

Electronic absorption spectrum of Ni2+ in lithium potassium sulphate single crystal

Single crystals of nickel-doped lithium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The bands have been assigned transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The crystal field parameters derived areDq=910cm^–1,B=890cm^–1 andC=3560cm^–1.The authors wish to express their thanks to Prof. K. Sreerama Murthy for his constant encouragement throughout this investigation. The authors are also thankful to Prof. Mihir Chowdhury, Indian Association for the cultivation of Science, Calcutta for giving permission to take the spectra.     

Mössbauer study of substituted barium ferrite BaFe11−x−y Co0.5Ti0.5Ni x ZnyO19−r

Substituted barium ferrite BaFe_11–x–y Co_0.5Ti_0.5Ni _x Zn_yO_19–r powders were prepared using a coprecipitation method and investigated by X-ray diffraction (XRD) and⁵⁷Fe Mössbauer spectroscopy. The results show that the as-prepared magnetic powders possess the typical hexagonal structure and demonstrate both a good dispersibility and a narrow particle size distribution. The hyperfine fields for all sites decrease slightly asx (ory) increases. The Ni²⁺ ions prefer to occupy the 2a and 12k sites, and Zn²⁺ ions occupy the 4f_IV site.     

Effects of pressure on magnetic interactions in the rare earth intermetallics R2Ni17

The Curie temperatures of Y₂Ni₁₇ and Dy₂Ni₁₇ were observed to vary with hydrostatic pressure at a rate of –0.44 K/kbar. The results for the compounds R₂Ni₁₇ were compared with previously reporteddT _c/dp data for R₂Co₁₇ and R₂Fe₁₇ and discussed in terms of simplified collective and localizedd-electron models. The former model suggests that R₂Ni₁₇ and R₂Co₁₇ are relatively far from the Stoner instability limit, while the compounds R₂Fe₁₇ approach very weak itinerant ferromagnetism. The slow pressure variation of the compensation temperature of Dy₂Ni₁₇, –0.03 K/kbar, was attributed to the insensitivity of the R-Ni interaction to interatomic spacing.     

Optical absorption spectrum of Ni2+ ions doped in sodium potassium sulphate single crystal

Single crystals of nickel-doped sodium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the observed bands could be made assuming the octahedral symmetry for the Ni^{2 +} ion in the crystal. The bands have been ascribed to transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The experimental and calculated energies are in good agreement. The crystal field parameters derived areDq= =880 cm^–1,B= 900cm^–1 andC=3600 cm^–1.One of the authors, Sujatha John expresses her thanks to the Secretary and the Principal, R. B. V. R. Reddy College, Hyderabad for according her permission to pursue the M. Phil. course.     

Stoichiometry of LiNiO2 Studied by Mössbauer Spectroscopy

From the ⁶¹Ni and ⁵⁷Fe Mössbauer spectroscopy data follows the cationic site assignment in Li_1–x Ni_1+x O₂. Our data explain the ferromagnetic properties of this material because of the appearance of Ni²⁺ (S=1) among Ni³⁺ (S=1/2) in Ni³⁺O₂ hexagonal planes. We have no evidence for the ferromagnetic interaction between the NiO₂ layers through the excess Ni²⁺ ions substituting the Li⁺ ions. The presence of Ni²⁺ found in the Ni³⁺O₂ planes explains the absence of the Jahn–Teller distortions probably because of the electronic transfer between the Ni³⁺ and Ni²⁺ ions.     

Diffusion of Au in amorphous Zr x Ni100−x alloys studied by Rutherford Backscattering Spectrometry

The diffusion coefficients (D) of Au in three binary amorphous Zr _x Ni_100–x (x=61, 65, and 67) alloys were measured in the temperature range 549–623 K using the technique of the Rutherford Backscattering Spectrometry (RBS). The D values were found to lie in the range 1.0×10^–21–9.0×10^–20 m²s^–1 for different alloys. The activation energy (Q) was calculated in each case on the basis of an observed Arrhenius temperature dependence of D. The activation energy was found to scale with the crystallization temperature (T _x) of the alloy. Other published measurements for Au diffusion in amorphous Zr-Ni alloys also appear to follow the scaling relation between Q and T _x.     

Magnetic properties of Fe and Ni films evaporated in poor vacuum

To examine the pressure dependence of magnetic characteristics of Fe and Ni films, the films were prepared in vacuum ranging from 10^–5 to 10^–2 torr.Saturation magnetizationM _s ^* , perpendicular anisotropyK ^* and coercive forceH _c for Fe and Ni films deposited at around 10^–5 torr were in good agreement with the values obtained by others. When the film thickness was less than 500 ,M _s ^* for Fe films increased with pressure, while it decreased monotonically for Ni films. At pressures between 2×10^–3 and 10^–2 torr,M _s ^* decreased rapidly for Fe but it increased slightly for Ni. This interesting behaviour was most marked with film thickness of about 500 . Corresponding to the change inM _s ^* , bothK ^* andH _c also changed with deposition pressure.The result should be explained in terms of the presence of Fe₄N, Fe₈N and Ni₃N, as well as the macroscopic and microscopic structures of films.     

Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

The kinetics of Ni₂Si growth from pure Ni and from Ni_0.93V_0.07 films on (111) and (100) silicon has been studied by the combination of He⁺ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4–5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.     

Synthesis and characterization of a large amount of branched Ni2Si nanowires

A large amount of Ni₂Si nanowires sheathed with amorphous silicon oxide has been generated from Ni substrates, for the first time, by thermal chemical vapor deposition using SiH₄ gas at 500 °C. The Ni₂Si nanowires obtained possess substantial amounts of branches (about 2-m length) grown on the main stems (about -–30 80nm diameter and -–10 20m length). High-resolution transmission electron microscopy and electron diffraction have revealed the orthorhombic Ni₂Si phase and the orientation. At the tail end along the branch grown on a stem an amorphous phase was also observed. The Raman spectrum was further used to characterize the product. A possible growth process of the branched Ni₂Si nanowires is briefly discussed. PACS 81.05.Bx; 81.07.Bc; 81.15.Gh; 87.64.Ee; 87.64.Je     

High-temperature strength of Ni3Al - Ni3Nb alloys

Conclusions The concentration dependences have been found for the bending and compression strength of Ni₃Al–Ni₃Nb alloys in the temperature range 20–1200 °, and the corresponding dependence for the tensile strength has been found at room temperature. It has been shown that the alloys with 45 and 90 wt.% Ni₃Nb are the strongest. The concentration dependences of the strength of these alloys have been compared with their physical properties.Translated from Izvestiya Vysshlkh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 7, pp. 55–59, July, 1969.     

The Hall effect in amorphous (Zr0.64Ni0.36)1−x M x alloys (M=Al,Ga)

Values of the room temperature Hall coefficients and electrical resistivity of amorphous melt spun (Zr_0.64Ni_0.36)_1–x Al _x and (Zr_0.64Ni_0.36)_1–x Ga _x alloys forx=0–0.25 are reported. Addition of Al or Ga to Zr_0.64Ni_0.36 dramatically increases the already positive Hall coefficient of this alloy and also increases the electrical resistivity and crystallization temperature.     

Optical absorption spectrum of Ni2+ doped in ammonium zinc sulphate

The optical absorption spectrum of Ni²⁺ ion doped in ammonium zinc sulphate has been studied at room and liquid air temperatures. From the nature and the positions of the bands a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The fine splitting of the³ T ₁ ¹ band at liquid air temperature has been successfully interpreted to be due to spin-orbit interaction. The crystal field and spin-orbit parameters derived areDq=1000 cm⁻¹;B=750 cm⁻¹;C=3.45B andξ=600 cm⁻¹.     

Silicide formation by furnace annealing of thin Si films on large-grained Ni substrates

Si films with a thickness of approximately 250 nm have been electron-beam evaporated on thick, large-grained Ni substrates (grain size a few mm to 1 cm in diameter). An in situ sputter cleaning procedure has been used to clean the Ni surface before the Si deposition. Thermal annealings have been performed in a vacuum furnace. Ni₂Si is the first phase that grows at temperatures between 240 °C and 300 °C as a laterally uniform interfacial layer with a diffusion-controlled kinetics. The layer thicknessx follows the growth lawx ²=kt, withk=k ₀ exp(-E _a k _B T), wherek ₀=6.3 × 10^–4cm 2/s andE _a=(1-1±0.1) eV. Because of the virtually infinite supply of Ni, annealing at 800 °C for 130min yields a Ni-based solid solution as the final phase. The results are compared with those reported in the literature on suicide formation by the reaction of a thin Ni film on Si substrates, as well as with those for interfacial phase formation in Ni/Zr bilayers.     

The optical gap of NiO

The nature of the optical absorption gap in NiO at 4.0 eV is investigated. It is found that this gap is due to a band to band transition, where an electron is taken out of the valence band and placed into the conduction band. The optical gap of 6.0 eV found in NiMgO is of a nature, where an electron is taken out of the oxygen 2p band and placed into the first affinity level of the Ni²⁺ ion (3d ⁸L»3d ⁹L^–1). The impurity band created in Ni_1–x Li _x O by the Li ions is found 2.3 eV below the bottom of the conduction band in agreement with model predictions.     

Order-disorder phase transition in Ni4W alloy

The order-disorder phase transition in Ni₄W alloy with a D1 _a superlattice was studied experimentally by x-ray structural analysis and theoretically by the Green function method. An experimental temperature dependence was obtained for the equilibrium parameter of long-range order for Ni₄W alloy. It was established that the order-disorder phase transition in the alloy is a first-order transition; the transition occurs through the two-phase region D1_a + A1. The Green function technique, with account for the pair-correlation functions, was used to describe the order-disorder transition for the D1 _a superlattice. The theoretical temperature dependence obtained for the equilibrium parameter of long-range order is in satisfactory agreement with the experimental curve.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 92–97, April, 1978.     

Resistometric and X-ray investigation of (Ni2Cu)1−x Sn x alloys

Resistometric measurements have revealed the approximate position of the solvus line in the isopleth phase diagram of (Ni₂Cu)_1–x Sn _x alloys for Sn content between 0 and 14 at.% and temperatures between 600 and 900°C. The data were analyzed on the ground of a model which takes into account their dynamic character. Within the two-phase region they indicate the existence of two different phase-states of the system. Control X-ray measurements have shown that in the high temperature region above approx. 700°C the second phase is of theDO ₃ structure. Our results are in variance with published data.These measurements were kindly supported by the Czech Grant Agency under Contract Nr. 106/93/513. The help of Mrs. A. Svobodová during the preparation and evaluation of X-ray measurements is gratefully acknowledged.