Raman and infrared spectra of ammonium selenate and lithium ammonium selenate

The Raman and infrared absorption spectra of (NH₄)₂ SeO₄, (ND₄)₂ SeO₄ and Li (NH₄) SeO₄ have been recorded at 300° K; while the spectra of the non-deuterated compounds have been recorded at 110° K also. (NH₄)₂ Se0₄ crystal exhibits 33 Raman lines, while LiNH₄SaO₄ shows 30 Raman lines at 300° K. Proper assignments have been given to the observed vibration frequencies. The SeO₄ ^?? ions and the (NH₄)⁺ ions are found to be highly distorted in these selenates. There is lowering of the N-H vibration frequencies due to hydrogen bonding. The present spectroscopic investigations do not reveal the existence of any phase transition in these selenates in the temperature region investigated.     

Paramagnetic resonance studies of Cu2+ doped in NH4Br

Electron Paramagnetic Resonance studies of Cu²⁺ doped in NH₄Br single crystals have been carried out for the first time. The room temperature data reveal that Cu²⁺ ions go predominantly to interstitial sites having square planar co-ordination of four Br^? ions. For this type of complexes the bromine: superhyperfine structure: is observed on the normal hyperfine structure lines of copper. Existence of other weak spectra indicates that a relatively few Cu⁺⁺ ions go substitutionally to (NH₄)⁺ ions, and are probably associated with a first or a second nearest neighbour cation vacancy, among the two, the latter being more predominant. However, the low temperature studies corresponding to the tetragonal phase of NH₄Br indicate that a number of Cu²⁺ ions at interstitial sites get readjusted to the lattice sites after phase transformation. The spectra in both the phases are analysed by the usual spin Hamiltonian method.     

Electron paramagnetic resonance of Mn2+ in (NH4)2SO4 single crystal

Electron paramagnetic resonance investigation of Mn²⁺ in (NH₄)₂SO₄ single crystal is discussed both in paraelectric and ferroelectric phases of the crystal. Mn²⁺ is found to substitute one of the two possible types (α andβ) of NH ₄ ⁺ ions and get associated with the second type of NH ₄ ⁺ vacancy, the vacancy being the second distant neighbour in thebc-plane. As The line joining Mn²⁺ substituted NH ₄ ⁺ site and NH ₄ ⁺ vacancy lies at an angle of 18° from the crystallographicb-axis in thebc-plane. As the temperature is lowered to ? 56° C the crystal becomes ferroelectric and the spectrum in the paraelectric phase splits into two from which it appears that two sets of Mn²⁺ sites which are magnetically equivalent in the paraelectric phase become inequivalent in the ferroelectric phase. The spin Hamiltonian analysis is presented for the spectrum in the paraelectric phase.     

Infrared spectrum of ferroelectric lithium hydrazinium sulphate [Li (N2H5) SO4]

Dielectric observations on lithium hydrazinium sulphate have shown earlier that it is ferroelectric over a range of temperatures from below ?15° C. to above 80° C. and a new type of hydrogen bond rearrangement which would allow the protons to migrate along the chain has also been suggested by others. The infrared spectrum of LiH _z S in the form of mull and as single crystal sections parallel and perpendicular to the ‘C’ axis exhibit about 21 well-defined absorption maxima. The position and the width of the maxima agree with the known structure of the crystal according to which the hydrazine group exists in the form of the hydrazinium ion, NH₂·NH ₃ ⁺ and the observed N⁺-H frequencies agree better with the new correlation curve given by R. S. Krishnan and K. Krishnan (1964). However it has been pointed out that from a comparative study of the new infrared spectra of hydrazonium sulphate and lithium ammonium sulphate that the absorption band at 969 cm.^?1 is due to N-N stretching vibration and that the fairly intense band between 2050–2170 cm.^?1 is due to the bending vibrations of the NH ₃ ⁺ group.     

Oxidation studies-VII

Kinetics of oxidation of hydrazine sulphate and hydroxylamine by Co³⁺ in nitric and sulphuric acid media at 10–15° C. were studied. In H₂SO₄ medium, kinetic evidence was obtained for complex formation between Co³⁺-Substrate for both substrates whereas no such evidence was found in HNO₃ medium. The effects of [H⁺], μ [HSO₄ ^?], [SO₄=], [Co²⁺] and temperature on the reaction rates were studied. An inverse dependence of the rates on [H⁺] was noticed in both media with both substrates but decreasing effect of [HSO₄ ^?] was observed only with NH₂OH in H₂SO₄ medium. Conclusions were drawn as to the nature of the active species: In H₂SO₄ medium for hydrazine sulphate, Co³⁺ (aq.) was concluded to be the active species; similarly for NH₂OH, CoOH²⁺ was the active species. In HNO₃ medium for both substrates CoOH²⁺ was the active oxidant. Nitrogen and Ammonia were found to be the products of oxidation with both substrates in both media. Stoichiometries were established and suitable mechanisms were proposed. The rate laws were formulated and the various equilibria and rate constants were evaluated.     

The1I6 state of Pr3+ in LaCl3 at 77°K

A single crystal of 5% Pr³⁺ in LaCl₃ was grown by Stockbarger’s method and its absorption spectrum at 77° K. recorded in the region 4200–5400 Å on a grating spectrograph having a dispersion of 5 Å/mm. in the first order. Polarization of the absorption lines has also been obtained. In the group of lines arising from¹I₆ ←³H₄ transition, six more lines in addition to the four previously known have been observed. Satisfactory analysis of all these ten lines is given. One additional Stark level in¹I₆ is established at 21407 cm.^?1 withμ=1. For a few lines the polarization results obtained here do not agree with those of previous workers but fit in satisfactorily in the analysis.     

Thermal expansion of ferroelectrics

Using the interference method the thermal expansion of lithium hydrazinium sulphate [Li(N₂H₅)SO₄] has been investigated in the temperature range ?170° C. to +220° C. The principal expansion coefficients along the crystallographic axes have been determined and at room temperature (25° C.) the values ofa _a,a _b anda _c are respectively 17·7, 13·5, and 43·0, ×10^?6 (°C.)^?1. The expansion coefficients are found to vary nonlinearly, and, in particular, along thec-axis the thermal expansion shows an anomalous behaviour between ?160°C. and ?60°C. and also in the neighbourhood of +130°C. These anomalies are explained as due to homomorphous transitions in which there is a reorientation of the ?NH ₊ ³ group about the N-N axis or a re-alignment of the ?NH₂ group.     

Oxidation studies

Studies on oxidation of water by cobaltic ions in perchloric, nitric and sulfuric acid media in the temperature range 20–30° C. at constant ionic strength of 2·2 M were carried out. An overall order of 3/2 for cobaltic ion concentration was observed in perchloric, nitric acid media and at low [Co³⁺]<4×10^?3 M in sulfuric acid medium. At high [Co³⁺] in sulfuric acid medium an order 2 was observed. In all the three acid media an inverse dependence of the rates on [H⁺] was noticed. From the experimental results, an acid-independent reaction path was inferred in perchloric and nitric acid media. The effect of ionic strength, HSO ₄ ^? and initially added cobaltous ions as well as temperature was studied. Suitable reaction schemes were suggested to explain the experimental results and activation energy values for some of the rate parameters were evaluated. Kinetic studies on oxidation of tertiary amyl and tertiary butyl alcohols in sulfuric acid medium and that of the former in perchloric acid medium were carried out. The reaction rates were found to vary linearly with [Co³⁺] and [Alcohol]. From the effect of acidity and of [HSO ₄ ^? ] in H₂SO₄ medium on the reaction rates it was concluded that in HClO₄ medium CoOH²⁺ species were the active entities while in H₂SO₄ medium Co³⁺ as well as CoOH²⁺ species were the active entities. The influence of ionic strength, temperature, etc., on the raction rates were studied and activation energy values for some rate constants were evaluated.     

Electron paramagnetic resonance of Mn2+ in NaF single crystals

The electron paramagnetic resonance of Mn²⁺ in NaF single crystals is investigated at different temperatures from 573° K to 93° K. Four different spectra designated as I, II, III₂ and III₄ are observed. Spectrum I consists of a single broad resonance corresponding to precipitated Mn²⁺ ions. Spectrum II is isotropic and centred nearg = 2.00. This spectrum corresponds to substitutional Mn²⁺ ions with remote charge compensating sites and therefore with local cubic symmetry. Spectrum III₂ withg = 2.014 and spectrum III₄ withg = 1.995 are also due to substitutional Mn²⁺ ions but subjected to tetragonal crystalline fields and are the same as those reported by earlier workers. Superhyperfine structure has been observed in spectra II, III₂ and III₄. The analysis of that structure in spectra II and III₂ has been carried out for the first time and the constants A_s, and A_σ are given. The spectra are analysed by the usual spin-Hamiltonian method.     

Temperature dependence of the knight shift of207Pb resonance in Na15Pb4 intermetallic compound

Knight shift of²⁰⁷Pb resonance in Na₁₅Pb₄ intermetallic compound has been determined in the range of temperatures between 120° K. and 480° K. The shift has been found to be negative with reference to²⁰⁷Pb resonance in solid lead nitrate and decreases in magnitude with increasing temperature. The results are discussed in the light of the electronic structure of the alloy.     

Paramagnetic resonance of Gd3+ in SmCl3·6H2O single crystals

The Paramagnetic Resonance of Gd³⁺ in SmCl₃·6H₂O single crystals, grown from solution, is studied at room temperature. A six line spectrum for H//Z and a seven line spectrum for H//X corresponding to ΔM=± 1 transitions are observed. Their angular variation in ZX plane from?=0° to?=90°, is studied and the spin-Hamiltonian analysis is presented. The probable amount of admixture of the next higher electronic state⁶P_7/2 with the ground state⁸S_7/2 is also estimated.     

The near ultraviolet absorption spectra ofortho- andmeta-thiocresols

The absorption spectra ofortho- andmeta-thiocresols have been studied in the present investigation. The ortho-thiocresol spectrum consists of about forty-five bands of rather a diffuse nature and in general low intensity in the region from 2873 Å to 2600 Å. The maximum number of bands is obtained by using a path length of 330 cm. for absorption, the temperature of the bulb being maintained at 14°C. Several of these bands are assigned as due tov-v-transitions. The (0, 0) band is chosen at 35386 cm.^?1 which is the strongest band on the longer wavelength side. Vibrational frequencies in the excited state have values 729, 957 and 1159 and combinations and overtones of these are present. Themeta-thiocresol spectrum consists of about forty bands of rather a diffuse nature and very weak intensities in the region from 2900 Å to 2590 Å. The maximum number of bands is obtained by using a path length 200 cm. for absorption and by keeping the temperature of the bulb at 20° C. The (0, 0) band is chosen to be that at 34793 cm.^?1 which is the strongest band on the longer wavelength side. Vibrational frequencies in the excited state have values 492, 611, 720, 845, 965, 1016 and 1155 cm.^?1 and combinations and overtones of these are present.     

Vinyl polymerization

Polymerization of Acrylamide initiated by cobaltic ions in aqueous solution at 15° C. and 20° C. in HClO₄ and H₂SO₄ media have been studied. Kinetics have been followed by determining the rate of cobaltic ion disappearance as well as monomer disappearance with variations in cobaltic, monomer and hydrogen ion concentrations, temperature, ionic strength, etc. Besides polymer reaction it has been observed that side reactions like water oxidation and monomer oxidation also contribute to rate of cobaltic ion disappearance. Certain anomalous results in H₂SO₄ medium have been observed. A reaction scheme involving CoOH²⁺ and Co³⁺ as initiators in HClO₄ and H₂SO₄ media respectively and mixed termination—mutual and linear—has been suggested. Certain rate parameters involving rate constants for initiation, propagation, termination and the corresponding activation energies have been evaluated.     

Phase Transition and Eigenvalue Degeneracy of a One Dimensional Anharmonic Oscillator

For a one dimensional lattice model with long range exponential interaction the problem of deriving the thermodynamic properties of the system reduces to the problem of determining the spectrum of a differential equation for a one dimensional anharmonic oscillator with potential αx² + βγx⁴ where γ is the inverse of the range of the interaction and α is a function of temperature which is positive at high temperatures and negative at low temperatures. It is proved that at low temperatures, α < 0, and in the limit γ → 0, (corresponding to an infinitely long range interaction) the spectrum becomes asymptotically degenerate. The relation of degeneracy to the occurrence of a phase transition is discussed and the generalization to higher dimensions is mentioned briefly.     

Raman spectrum of dimethyl sulfoxide (DMSO) and the influence of solvents

The Raman spectrum of DMSO is recorded with a Hilger two-prism spectrograph andλ 4358 Å excitation. In addition to all the Raman lines reported earlier, six new lines at 898, 925, 1223, 1309, 2811 and 2871 cm.^?1 are observed and tentative assignments are given. The influence of solvents (CCl₄, CHCl₃, CH₃COOH) on the S=O bond is also studied. A shift from the liquid phase value,i.e., 1043 cm.^?1 to 1054, 1052 and 1009 cm.^?1 in the respective solvents is observed. The possibilities of association effects and hydrogen bonding are discussed.     

Characterization of ZnO: Al films deposited by r.f. magnetron-sputtering at low temperature

Transparent conducting ZnO: Al thin films with good adhesion and low resistivity have been prepared on organic substrates and Corning 7059 glass substrates by r.f. magnetron-sputtering technique at low substrate temperature (25–210°C). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed. High quality films with resistivity as low as 1.0 x 10^-3Ω·cm and 8.4 x 10^-4Ω·cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates.     

Emission spectrum of bromine excited in the presence of argon—part I

Bromine was excited by an uncondensed transformer discharge in the presence of argon. The spectrum obtained was found to be different from what one gets without the presence of a foreign gas and consists of (1) a short discrete band system in the region 3150–2970 Å, (2) an extensive discrete band system in the region 2950–2670 Å, (3) a short and weak discrete system in the region 2660–2590 Å and a set of diffuse bands in the region 3340–3190 Å. The wavelengths and wave numbers of the band heads of the system 2950–2670 Å, as obtained from the measurements of the plates taken on the first order 21-ft. grating spectrograph, are given along with the vibrational analysis. This system is shown to be due to a transition from an upper electronic state at 51802 cm.^-1 with ω′_e = 150·5 cm.^-1 and ω′_e X′_e = 1·15 cm.^-1 to the well known³ II _α (O₂ ⁺) state at 15918 cm.^-1     

Oxidation of aldehydes by aqueous Ce (IV) in nitric acid

The kinetics of oxidation of acetaldehyde (at 20°, 31° and 40° C.), propionaldehyde (at 15°, 25° and 35° C.) and chloral hydrate (40°, 50° and 60° C.) by ceric nitrate in nitric acid medium [(H⁺) ≈ 0 · 5?1 · 5 M] were studied. The reactions were followed by determining rates of ceric disappearance for variations in [Ce⁴⁺], [RCHO], [H⁺], μ, temperature, etc. The stoichiometry, ΔCe⁴⁺ / Δ CH₃CHO ≈ 2 was established. The reactions were found to be 2nd Order—first order each with respect to [Ce⁴⁺] and [RCHO]. No complex formation between Ce⁴⁺ and aldehydes was observed. Neutral Ce (NO₃)₄ (H₂O)₂ and diol of the aldehyde were assumed the active species. The rate and thermodynamic data were calculated and discussed. The rates of oxidation were correlated with the structures of the aldehydes.     

Magnetic properties and microstructure of HDDR isotropic Nd-Dy-Fe-Co-B bonded magnets with high coercivity

The effect of small amount of Co and Dy addition on the magnetic properties of HDDR isotropic Nd-Dy-Fe-Co-B bonded magnets was investigated. The experimental results show that the intrinsic coercivity H_cj and the reversible temperature coefficient of remanence of (Nd_0.65 Dy_0.35)_12.5-(Fe_0.9Co_0.1)₈₁B_6.5 magnet were 1.53 MA·m^-1(19.3 kOe) and -0.059%/°C (25–155°C), respectively. The high coercivity and low temperature coefficient of the magnet are due to the enhanced anisotropy field, increased Curie temperature and improved microstructure by Dy and Co addition.     

Properties of GaAs single crystals grown by molecular beam epitaxy at low temperatures

Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The results show that excessive arsenic atoms of about 10²⁰ cm⁻³ exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs. The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing above 300°C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing. The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity, and the effects of backgating or sidegating are effectively restrained.