Lithium in In2S3

The electrochemical insertion of lithium into β-In₂S₃ at different concentrations has been investigated by means of γγ-Perturbed Angular Correlations measurements using implanted radioactive ¹¹¹In nuclei. The study of the hyperfine interactions of the ¹¹¹Cd nuclei during the decay ¹¹¹In(EC)¹¹¹Cd allowed to determine the evolution of the three observed electric field gradients at different temperatures and lithium contents. This study reveals a great difference of behavior between the three indium sites of the structure, and shows the mobility of indium ions and their partial reduction after lithium insertion. In₂S₃ is good model material to study the properties of more complex materials based on this structure, which may be used as electrodes for lithium-ion batteries. This revised version was published online in September 2006 with corrections to the Cover Date.     

The electric field gradient of111Cd in an α-Al2O3 single crystal

Radioactive¹¹¹In⁺ ions were implanted into an α-Al₂O₃ single crystal. The hyperfine parameters of¹¹¹Cd at substitutional Al lattice sites were identified by measuring the perturbed angular correlation for different sample orientations. The electric field gradientV _zz =1.04(17)·10²²V/m² was obtained from the quadrupole coupling constant. This result is compared with the efg values of²⁷Al in α-alumina and¹¹¹Cd in α-Fe₂O₃, which also has the corundum structure. Two additional fractions with broad frequency distributions were observed, one of which is attributed to¹¹¹Cd atoms in a strongly distorted Al₂O₃-lattice.     

The EFG of the In-O-Bond In2O3, AgO and Ag2O

PAC measurements on¹¹¹In in In₂O₃, AgO and Ag₂O were performed to study the influence of different oxygen coordinations to the EFG.¹¹¹In was implanted at 500keV; in addition, AgO and Ag₂O were irradiated in the cyclotron to produce¹¹¹In via the (α, 2n) reaction. Using the point charge model and the known lattice structure of the oxides, the antishielding factor was calculated; it shows a strong dependence on the In-O bondlength.     

Structural phase transition of Rh2O3 studied via PAC

The structural phase transition from α-Rh₂O₃ to β-Rh₂O₃ has been studied via the PAC method on dilute¹¹¹Cd impurity atoms implanted into α-Rh₂O₃. The measured antishielding factor β=112 (2) in the α-phase is similar to that found for¹¹¹Cd in other oxides with corundum structure (Al₂O₃. Cr₂O₃, Fe₂O₃). Oxygen with different crystallographic matrices show a pronounced correlation of the electric field gradient with the NN oxygen coordination.     

On bound state computations in three- and four-electron atomic systems

A variational approach is developed for bound state calculations in three- and four-electron atomic systems. This approach can be applied to determine, in principle, an arbitrary bound state in three- and four-electron ions and atoms. Our variational wave functions are constructed from four- and five-body Gaussoids that respectively depend on six (r ₁₂, r ₁₃, r ₁₄, r ₂₃, r ₂₄, r ₃₄) and ten (r ₁₂, r ₁₃, r ₁₄, r ₁₅, r ₂₃, r ₂₄, r ₂₅, r ₃₄, r ₃₅ and r ₄₅) relative coordinates. The approach allows operating with the more than one electron spin functions. In particular, the trial wave functions for the ¹ S states in four-electron atomic systems include the two independent spin functions χ₁ = αβαβ + βαβα − βααβ − αββα and χ₂ = 2ααββ + 2ββαα − βααβ − αββα − βαβα − αβαβ. We also discuss the construction of variational wave functions for the excited 2³ S states in four- electron atomic systems.     

Ion-induced phase transition in the Au–In system

The Au–In equilibrium phase diagram exhibits a large number of intermetallic phases which have recently been explored via perturbed angular correlation spectroscopy, using alloyed and/or diffused ¹¹¹In probes. In the present work we report on the phase transition from Au₇In₃ (hexagonal, γ'-phase) to Au₉In₄ (γ-brass phase) induced via Xe- or Ar-ion implantations at 80 K. We compare the hyperfine parameters with those obtained in thermal equilibrium and after quenching, and argue that ion beam mixing and fast cooling in the condensation phase of thermal (local) spikes are the predominant mechanisms to interpret our findings. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of annealing on the optical properties of In2Te3 thin films

2 Te₃ thin films of different thickness were prepared in a vacuum of 10^-5 Torr onto glass and quartz substrates held at about 300 K during the deposition process. X-ray diffraction analysis showed that the prepared samples in bulk or as-deposited thin-film forms were in an amorphous state. On annealing at 573 K, films have a β-phase polycrystalline structure. Transmittance and reflectance measurements in the spectral range of 400–2500 nm for films deposited onto quartz substrates were used to calculate the optical constants (the refractive index n, the absorption index k and the absorption coefficient α) for In₂Te₃ films, either as-deposited or annealed at different temperatures. The refractive index has anomalous behavior in the region of the fundamental absorption edge. The allowed optical transitions were found to be nondirect transitions, with an optical gap of 1.02 eV for the samples under test. The effect of annealing on the optical gap is interpreted in terms of the density of states proposed by Mott and Davis. Received: 22 June 1997/Accepted: 9 July 1997     

Spin dynamics of charge carriers in the process of their localization in α’-(BEDT-TTF)<Subscript>2</Subscript>IBr<Subscript>2</Subscript> single crystals

Sharp changes in the integral intensity and linewidth of the ESR spectrum that accompany the localization of the charge carriers have been revealed in α’-(BEDT-TTF)₂IBr₂ crystals. It has been found that the types of localization in two compounds under investigation are different: charge carriers in β″-(BEDT-TTF)₄NH₄[Cr(C₂O₄)₃] are localized on irregular defects of the crystal lattice, whereas charge carriers in α’-(BEDT-TTF)₂IBr₂ are localized at the regular positions of the unit cell. The exchange narrowing of the ESR line and a sharp decrease in the dc and ac magnetic susceptibilities are observed in α’-(BEDT-TTF)₂IBr₂ at low temperatures T < 50 K. The dc and ac magnetic susceptibilities observed in α’-(BEDT-TTF)₂IBr₂ at high temperatures T > 50 K differ from each other, because the thermally activated hopping frequency of the charge carriers is higher than the frequency of the measuring UHF field of an ESR spectrometer.     

Synthesis and characterization of sol-gel derived Mn2+ doped In2S3 nanocrystallites embedded in a silica matrix

Mn²⁺ doped In₂S₃–SiO₂ nanocomposite thin films were synthesized by sol-gel technique. The films were annealed in air at different temperatures (473–623 K) and characterized by optical, microstructural and electron spin resonance (ESR) study. Optical transmittance study revealed the manifestation of quantum size effect while ESR indicated the presence of manganese in indium sulphide as dispersed dopant rather than manganese cluster.     

Implantation of the 111In/Cd Probe as InO− Ion for Radioisotope Tracer Studies

A radioisotope ion implanter has been developed using a cesium-sputtering, negative ion source, which offers versatility and sustained operation. Employing the molecular ¹¹¹In¹⁶O⁻ ion, μCi activities of the radioisotope probe ¹¹¹In/Cd have been implanted into different material hosts. The implanted tracer activity has been shown to be sufficient for LTNO, NMRON and PAC. A new NMRON resonance for ¹¹¹InAg was observed at 75.08 MHz. In₂O₃ powder performed well as the radioisotope carrier in the ion source, with the ratio of radioisotope and parasitic ion current being typically 4 × 10⁻⁴.     

Local magnetic susceptibility in γ- and α-Ce

The local susceptibility, below and above the γ-α transition, was measured with the DPAC method using the¹⁴⁰Ce probe. The ratio β between the local and the applied field was β_γ=1.20(2) and β_α=1.13(1) at 295 K. The latter value is larger than expected for a completely delocalized 4f electron.     

Hyperfine interactions of111Cd in ion-implanted face centered cubic cobalt

The magnetic-dipole and electric-quadrupole hyperfine interactions of¹¹¹Cd probes in fcc cobalt after implantation of radioactive¹¹¹In⁺ ions have been investigated by PAC measurements with fast BaF₂ detectors. Six different sites of the probe atoms could be distinguished and characterized by their hyperfine parameters and annealing behaviour. Besides the substitutional site, three sites are assigned to In-vacancy complexes which are formed athermally in the implantation process or by thermally-activated trapping of lattice defects in annealing stage III. The remaining two sites are attributed to In located in stacking faults or hcp regions of the host. Systematic trends of impurity hyperfine fields in defect sites become evident from a comparison with other impurity-host combinations. The temperature dependence of the magnetic hyperfine fields has been measured between 20 K and 390 K. Large differences found for the various sites are discussed.     

Oxidation of indium implanted aluminium studied by the Rutherford backscattering and perturbed angular correlation methods

Aluminium foils oversaturated with 5.10¹⁵/cm² implanted¹¹⁵In⁺ ions were oxidized in 200 mbar oxygen or vacuum annealed at 370–870 K. The samples were analyzed by the Rutherford backscattering (RBS) and perturbed angular correlation (PAC) techniques, using some 10¹¹/cm² implanted radioactive¹¹¹In tracers. Furthermore, the oxygen surface profiles were also scanned with high resolution by using the nuclear resonance technique (NRA). The formation of passivating Al₂O₃ surface layers, preventing deeper oxygen diffusion and the indium diffusion into these oxidized surface layers and into the bulk, were studied. Several quadrupole interaction frequencies previously attributed to strained cubic indium precipitates and indium (-vacancy) clusters were observed. When the samples were oxidized above 750 K, the formation of In-O complexes and of substitutional¹¹¹In in Al₂O₃ was observed.     

Perturbed angular correlation experiments on111In in oxidized AgCd alloy

The hyperfine interaction of¹¹¹Cd probes in preoxidized and α-irradiated Ag_0.94Cd_0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of¹¹¹Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very similar to the ones observed after α-irradiation.     

Residual impurity effects on the magnetic ordering in α-Mn observed by hyperfine interaction

We report on the lattice location of indium in and the magnetic ordering of manganese in its α- and β-phases, as seen by perturbed angular correlation. Quadrupole interaction spectra show that indium prefers to replace Mn atoms of type I in α-Mn, but replaces type II atoms in the β-Mn structure. The interaction strength equalseQV _zz /h=3.6 (6) MHz in α-Mn and 172.3 (3) MHz with ν=0.13 (1) in β-Mn. No magnetic ordering down to 4.2 K was observed in β-Mn, while belowT _N =95 K in the α-Mn phase, a magnetic hyperfine interaction appears indicating two distinct magnetic probe environments. The hyperfine field, when measured atT=4.2 K, equals for 70% of the probes 6.33 (1) T, while the remaining fraction senses a 3.10 (4) T field. The magnitudes of the hyperfine fields are essentially unaffected by a variety of conditions in the sample preparation. The ordering temperature, on the contrary, turns out to be rather sensitive to residual impurities especially any oxygen contamination.     

Polymorphic Phase Transformation in In2La and CeIn2

Nuclear quadrupole interactions of ¹¹¹Cd probes in In₂La and CeIn₂ were measured using perturbed angular correlation of gamma rays (PAC). Near room temperature, a single non-axially symmetric quadrupole interaction was observed in each compound, with ω ₀ = eQV _zz /ℏ = 78.8(2) Mrad/s and η = 0.312(1) for In₂La at 11°C and ω ₀ = 80(1) Mrad/s and η = 0.29(2) for CeIn₂ at 34°C. The observed non-axial symmetry is consistent with the reported CeCu₂ structure of the phases. The non-axially symmetric interactions were replaced completely by axially symmetric interactions (η = 0) at 524°C, with ω ₀ = 101.0(1) Mrad/s in In₂La and ω ₀ = 96.9(4) Mrad/s in CeIn₂. The change in symmetry is attributed to a polymorphic phase transformation. Based on symmetry information from the quadrupole interaction and on chemical arguments, it is proposed that high-temperature phases of In₂La and CeIn₂ both have the AlB₂ (C32) structure.     

Effect of Mg2+ on the Magnetic Compensation of Lithium–Chromium Ferrite

PAC measurements on ¹¹¹In(¹¹¹Cd) implanted and thermally treated α-Fe have shown an indication for a cubic defect with the ¹¹¹Cd probe in the centre of it. The measured room temperature (R. T.) magnetic hyperfine fields are B _hf1 = −38.4(8) T for substitution and B _hf2 = +11.5(3) T for the cubic defect. Additionally, probes with pure quadrupole frequency distributions were observed, which are incorporated in surface contaminations.     

PAC study on111Cd in antiferromagnetic CuO

400 keV¹¹¹In⁺ ions were implanted into CuO powder. After annealing at 570 K, more than 50% of the implants were found on substitutional sites in the monoclinic CuO lattice. PAC-spectra taken below the Néel temperatureT _N≈230 K revealed a broadening of the quadrupole spectrum and additional satellite frequencies caused by combined electric and magnetic hyperfine interaction. Assuming that the orientation of the electric field gradient is given by the point charge model and taking the 〈010〉 direction of the supertransferred fieldB _tr in CuO from neutron diffraction, we find a Larmor frequency of ω_L≈40 MHz corresponding toB _tr≈2.7 T at 60 K. Supported in part by BMFT under contract FK213N54930.     

Oxidation in the system InNi observed with pac

The oxidation of¹¹¹In implanted into Nickel was investigated with the PAC method. The samples heated in oxygen at 295–1223 K exhibit two fractions of oxidized In atoms, one clearly indentified as¹¹¹InNiO. The temperature dependence of the Lamor frequency of¹¹¹In in antiferromagnetic NiO was measured. The second fraction shows broadly distributed PAC parameters and is attributed to the trapping of interstitial oxygen at the In atom. The similarity between its quadrupole interaction parameters and those found for other fcc metals indicates the formation of similar InO_x complexes by the same mechanism in all fcc metals.     

Polarized fluorescence of β-carotene and related polyenes

The spectral and polarization characteristics of trans-isomers ofβ-carotene, lycopene, retinal, and 1,6-diphenylhexatriene (DPH) in solutions have been investigated by the methods of polarized fluorescence and semiempirical calculations of AM1 and RM3. The high and constant values of the degree of polarization P ∼0.46, closely coinciding with the limiting value P₀=0.5, according to the S₂→S₀-fluorescence and S₂←S₀-fluorescence excitation spectra ofβ-carotene and lycopene in n-hexane at room temperature and also high and coinciding according to the S₁→S₀-fluorescence and S₂←S₀-fluorescence excitation spectra for retinal in EPA at 77 K and DPH in a polyvinylbutyral film, point to the coincidence of the directions of absorption and emission oscillators. These oscillators are aligned along the major axis of the polyene molecule, and the longwave S₂←S₀-absorption band is formed only by one electronic¹B _u ⁺ ←¹A _g ⁻ -transition. The oscillators of shortwave S_a←S₀-absorption bands are aligned at an angle to the oscillators of the S₂←S₀-transitions, which is related to the distortions in the structure of molecules (β-carotene, lycopene) or, as in the case of DPH, to the influence of transitions localized on the orbitals of phenyl rings and polarized perpendicularly to the major axis of the molecule. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 69–74, January–February, 2000.