Liquid Air Temperature Research Articles

Crystal Field and Spin-Orbit Effects in the Optical Spectrum of Ni2+Ions Doped in Ammonium Aluminium Sulphate Single Crystal

Abstract The optical absorption spectrum of Ni2+ ions doped in ammonium aluminium sulphate single crystal has been studied at room and liquid air temperatures. From the nature and otner details of the spectrum, the crystal is found to have an octahedral symmetry. The fine splitting of the 3T1g (F) band at liquid air temperature has been interpreted due to spinorbit interaction. A weak band observed at 16845 cm−1 has been assigned to the vibrational mode of SO4 molecule. From a detailed analysis of the bands of the spectrum, the crystal parameters derived are: B = 678 cm−1; C = 3.75 B; Dq = 1030 cm−1 and ξ = 600 cm−1

Phonons in CdBr2(1-x)I2x: a mixed crystal with competing structures

Phonons in the mixed crystal system CdBr2(1-x)I2x have been studied by infrared absorption and Raman spectroscopies for selected concentrations in the range O<x<1 at liquid air temperature. For x=0.43 the Raman spectra at 300, 85 and 10K are compared. The shear-type rigid-layer E2phonon characteristic of the 4H polytype C6v4 CdI2 structure to the D3d5 structure of CdBr2 is evident. The concentration dependence of the multi-mode behaviour observed for the two Raman-active modes common to the two structures is discussed in terms of an averaged nearest-neighbour interaction between cadmium and halogen layers. The appearance of weak features in the Raman spectra associated with disorder-induced scattering from acoustic and polar optical phonons is also discussed.

Absorption spectrum of octahedral CoCl4(H2O)2 units in [(CH3)3NH]CoCl3�2H2O single crystal

The optical absorption spectrum of the octahedral moiety CoCl4(H2O)2 in single crystal [(CH3)3NH]CoCl3·2H2O has been studied at room and liquidair temperatures. The observed ambient bands at 6800, 16,300, and 19,000 cm−1 have been assigned, respectively, to the transitions4 T 1(F) →4 T 2(F),4 A 2(F), and4 T 1 (P). The crystal field parameters evaluated areD q =B=850 cm−1, andC=4.63B. At liquid-air temperatures the4 T 1(P) band is seen to split into the expected four componentsΓ 7,Γ 8,Γ 8, andΓ 6, due to spin-orbit coupling, and the coupling coefficientξ was computed to be 525 cm−1.

Absorption spectrum of Ni2+ doped in NH4Br single crystal

The optical absorption spectrum of Ni2+ doped in NH4Br single crystals has been studied at room and liquid-air temperatures. The observed ambient bands at 6300, 11,600, 13,400, 18,500, and 20,000 cm−1 have been assigned, respectively, to the transitions3A2(F) →3T2(F),3T1(F),1E(D),1T2(D and3T1(P). The crystal field parameters evaluated areDq=630 cm−1,B=850 cm−1, andC=3600 cm−1. In assigning the location of Ni2+ ions within the lattice, evaluations are made of the (limited) extant comparable data. It is then concluded that Ni2+ enters an octahedral interstitial, rather than a substitutional, site. It is surrounded by four bromide ions, in a plane, with two polarized water molecules at the opposing fifth and sixth positions.

Electrical conductivity, structure and hall effect measurements of InSe films

Stoichiometric InSe films were prepared by discrete evaporation using spectrally pure (99.999%) InSe powder in a residual pressure of about 4×10 −6 Torr. The thickness of the films was varied from 500 to 3000 Å. The elctrical conductivity of the films was measured by Van der Pauw's method. The as-deposited films had an amorphous structure as observed with an electron microscope. Thermal annealing was carried out through a number of annealing cycles and a transformation to a crystalline state during the process was evidenced by the electron micrographs. Conductivity measurements were made on the amorphous films from the transition temperature to liquid air temperature and the activation energies were calculated from the variation in conductivity with temperature. The density of states at the Fermi level was also calculated at low temperatures. Hall effect measurements were made on the annealed films and the Hall mobility μ H, the Hall coefficient R H and the carrier concentration n were evaluated.

Optical absorption spectrum of Ni2+ ion doped in synthetic lecontite

The optical absorption spectrum of Ni2+ ion doped in lecontite (sodium ammonium sulphate dihydrate) single crystal has been studied at room and liquid air temperatures. All the bands could be assigned assumingOh symmetry for the Ni2+ ion in the crystal. The splitting of3T1g (F) band at liquid air temperature has been attributed to spin-orbit interaction. The crystal field and spin-orbit parameters derived areDq=1000 cm−1;B=740 cm−1;C/B=4.27 and ζ=600 cm−1. All the bands observed show a blue shift when the crystal was cooled to liquid air temperature.

EPR and Mössbauer spectroscopic studies on metal complexes of pectic acid and their derivatives

Foods are more and more deficient in Mg and trace metals, due to the use of increasing amounts of NPK fertilisers, liming and high costs of trace metal fertilization as well as to the purification and refinement of raw nutriments. Recently, for the substitution of these metals, instead of inorganic salts or artificial metal chelates, metal complexes of biopolymers have been used [1], which, administered per os to vertebrates, can be absorbed and utilized without harmful side effects. Metal bonds in biopolymers are presumably similar to those in foods, and therefore will be studied by EPR and Mössbauer spectroscopy. Pectic acid (PAH), which contains polygalacturonic acid and some neutral carbohydrates, e.g., rhamnose, was prepared by the alkaline hydrolysis of pectin [1]. Derivatives of PAH as pectic acid dinitrate (PA)(NO 3) 2H and pectic acid disulphate (PA(SO 4) 2H 3 were obtained by treatment of PAH with conc. HNO 3 [2] and with the N,N-dimethyl formamidesulphur trioxide complex [3a, b], respectively. We have produced metal pectates as insoluble colour gels by the reaction of PAH with Cr(III)-, MoO(III)-, Fe(III)-, Mn(II)-, VO(II)-, Cu(II)-, Fe(II)-, Co(II)- ir Ni(II)-sulphate in aqueous solutions [1] and metal complexes of PAH derivatives as water soluble compounds. The EPR data of PAH gel doped with Mn 2+, Cu 2+ and VO 2+ ions show outer-sphere arrangement (Table I) similar to Ca alginate and agarose gels [4] t001 EPR Data for Mn 2+, VO 2+ and Cu 2+ Ions Doped in Various Samples. Metal ion Mn 2+ VO 2+ Cu 2+ Host lattice A iso (G) hpf split. Δ v (G) line width A iso (G) A∥ (G) A⊥ (G) g∥ g⊥ A∥ (G) hpf split. hpf-spliting spect. split. H 2O −95.0 30.4 119.7 203 78 2.422 2.087 −118.5 PAH −96.0 64; 28 112.2 195.6 70.5 2.403 2.081 −120 PA(SO 4) 2H 3 −94.7 41; 61; 82 113.9 195.2 73.2 2.376 2.089 −131 PA(NO 3) 2H −91.8 36 (1) 114.4 196.1 73.6 2.318 2.070 −154 (2) 108.5 187.8 68.9 Oxalate −91.1 22.9 103 180 65 2.318 2.071 −151.5 t002 Mössbauer Parameters for Iron(II) and Iron(III) Compounds at the Temperature of Liquid Air. Compound I.S. (mm s −1) Q.S. (mm s t 1 ̄ ) FeSO 4·7H 2O 1.48 3.4 Fe(II)alginate 1.42 3.21 Fe(PA) 2 1.40 3.15 Fe 3[PA(SO 4) 2] 2 1.37 3.08 Fe[PA(NO 3) 2] 2 1.40 3.05 Fe(II)-Dowex-Al Chelating Resin 1.30 2.91 Fe(PA) 3 0.45 0.90 Fe[PA(SO 4) 2] 0.40 0.60 Fe[PA(NO 3) 2] 3 0.46 0 Fe 2(SO 4) 3 0.65 0 doped with Mn 2+ and Cu 2+ ions. In the case of (PA)(SO 4) 2H 3 doped with Mn 2+, Cu 2+ and VO 2+ ions we have also found outer-sphere complexes in the hydrated (freeze dried) state. (PA)(NO 3) 2H doped with Mn 2+ ions also forms an outer-sphere complex, however, with Cu 2+ ions it results in an inner-sphere complex and with VO 2+ ions it gives both types of complexes: (1) outer-sphere and (2) inner-sphere arrangements (Table I). After dehydration (at 105 °C) of fully hydrated samples with an outer-sphere arrangement, EPR parameters will change due to transition of (1) to (2), however, in the case of inner-sphere complexes practically no change in EPR parameters can be observed [5a,b, 6]. The quadrupole splitting (Q.S.) value in the Mössbauer spectra of freeze dried iron(II) pectate also shows an outer-sphere arrangement (Table II). After dehydration (at 105 °C) the value of Q.S. decreased from 3.15 to 2.91 mm·s −1 [7, 8]. In the case of PAH derivatives the Q.S. values decreased with the decrease of water content in the first coordination sphere of iron(II). The Q.S. values of iron(III)-complexes show inner-sphere coordination with polynuclear structure [7, 8]. The structure of inner-sphere complexes will be studied by IR spectroscopy (see paper). According to animal and human investigations, Mg and transition metal complexes of PAH in gel or dehydrated form are suitable for per os treatment of iron-deficient anaemia, Mg-deficient ischemic heart disease [9] and all trace-metal deficient diseases. Fe[(PA)(NO 3) 2] 3 was applicable for parenteral, i.e., intravenous administration of iron(III) to pigs. Unfortunately, however, Fe[(PA)(SO 4) 2] 3 was found to be toxic.

Optical absorption spectrum of Cr3+ in natural ruby

Two sharp line-like bands calledN andR lines on the red side, a close doublet (B lines) on the violet side and two broad bands are observed for natural ruby. At liquid air temperature the splitting ofR line was found and also three sharp-bands calledR, R′ andB lines are identified with spin-forbidden transitions of2E,2T1 and2T2. The two broad bands calledU band andY band are assigned accordingly to the spin-allowed transitions4T2 and4T1 respectively. The observed bands of natural ruby have been attributed to Cr3+ ion in an octahedral environment with trigonal distortion. The crystal field parameters which gave a good fit to the observed band positions areB=732 cm−1,C=4.25B,Dq=1830 cm−1,V=−1996 cm−1 andλ=34 cm−1.

Determination of lifetime and diffusion length in silicon solar cells by self-biased (photovoltage) capacitance measurements

Many methods have been developed for the measurement of the diffusion length and lifetime of minority carriers in p-n junction solar cells. This paper presents a new technique for the measurement of these parameters, based on capacitance measurements in forward-bias condition at room and liquid air temperatures. In this experiment the solar cell was not biased by an external dc source, but was forward-biased by its own photovoltage generated by illumination. The results give 135 um diffusion length and 5.2 µsec lifetime of the minority carriers in a n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -p Si-solar cell.

Effect of impregnation, compression and temperature on electric strength of polythene and polypropylene

The effect of impregnation and compression on the electric strengths of polythene and polypropylene has been investigated. Measurements have been made over the temperature range −195 to + 20°C. Four impregnants were used: The dipolar liquids hexachiorodiphenyl, trichiorodiphenyl and dibutyl phthalate and nonpolar transformer oil. At room temperature, the impulse strengths of polythene and polypropylene are substantially increased by impregnation with certain of the dipolar liquids. Similar, although smaller, increases are found in the DC strength of polypropylene impregnated with any of the dipolar liquids. Transformer oil produces no improvements in the DC or impulse strengths of either of the two polymers. Using either of the chlorinated diphenyls as the impregnant, the DC strength of polythene is increased for all temperatures below the freezing points of the impregnants. Both the DC and impulse strengths are increased at liquid-air temperatures for polypropylene impregnated with trichlorodiphenyl. Compression improves the DC and impulse electric strengths of polythene. A mechanism of breakdown has been proposed, based on the presence of defects in the polymers. The defects initiate breakdown, and improvement in the electric strength results from their partial removal or filling by pressure or impregnation.

Cryostat for low temperature x-irradiation and electron paramagnetic resonance

A cryostat for x-irradiation of solid samples at liquid air temperature is described. The design of the sample mount in the cryostat enables quick transfer of the sample after x-irradiation into EPR cavity to facilitate EPR study without warming the sample.

Spectroscopic studies of transition metal ions in spessartine garnet

From optical absorption studies at room and liquid air temperatures and from Mossbauer spectrum, the absorption bands of spessartine garnet are attributed to Mn2+ and Fe2+ ions. The energy matrices ofd5 andd6 configurations are solved and the experimental data of Mn2+ and Fe2+ bands are fitted with the calculated values to solve for the Racah and crystal field parameters.

Measurements of gaseous lead alkyls in polluted atmospheres

The gaseous lead alkyls in ambient air were collected by enrichment in an adsorption tube at liquid air temperature. The desorbed lead alkyls were analyzed by atomic adsorption spectrometry. The measured concentrations of the gaseous lead alkyls vary between 0.001 μm −3 in the environment of Frankfurt/Main and 0.2μgm −3 in a city-street with high traffic-density. Paniculate lead was simultaneously measured. The ratio of gaseous organic lead to particulate lead varies with time and space between 1 and 20%. Within a street canyon particulate lead concentrations decrease more rapidly with altitude than the gaseous lead compounds. Chromatographie separation of lead alkyl samples showed that the more volatile and chemically more stable tetra-methyl-lead (TML) represents roughly 3 4 of gaseous lead in urban atmosphere.

Metastable structures of liquid-quenched and vapour-quenched antimony films

Antimony foils/films have been prepared by liquid-quenching and by vapour-quenching. (1) Simple cubic (a=3.16 A), (2) f c c (a=4.61 A), (3) tetragonal (a=3.01 A, c=4.96 A and c/a=1.64) structures, and (4) a new rhombohedral (aH=4.12 A, cH=10.26 A and cH/aH=2.49) metastable structure have been observed in splat-quenched foils. The metastable rhombohedral phase transforms to the equilibrium rhombohedral phase (aH=4.30 A, cH=11.27 A and cH/aH=2.62) on heating. The simple cubic, f c c and tetragonal phases are converted in to a hexagonal close-packed (a=3.33 A, c=5.23 A and c/a=1.57) structure on heating in the electron microscope. The simple cubic and h c p phases correspond to the known high-pressure phases of antimony. The h c p phase does not transform on further heating. Films prepared by vapour deposition on substrates held at room temperature show the same metastable f c c and rhombohedral phases as observed in splat-quenched foils, in addition to the equilibrium rhombohedral phase. On heating, these metastable phases transform in the same way as the splat-quenched specimens. The films deposited at liquid air temperature are amorphous; on electron-beam heating, these crystallize first to an unidentified complicated structure and then to the equilibrium structure.

Metastable structures of splat-cooled and vapour- depodited lead and antimony films

An apparatus for splat quenching in a vacuum and in controlling ambients by the “gun” technique was set up and a cooling rate of approximately 10 8 K s −1 was achieved. Splat-quenched lead foils exhibit an h.c.p. structure which transforms to the equilibrium f.c.c. structure at temperatures above 270°C and corresponds to the high pressure phase of lead. Antimony foils prepared by splat quenching show the existence of simple cubic, f.c.c. tetragonal and distorted rhombohedral metastable structures. The metastable rhombohedral phase tranforms to the equilibrium rhombohedral phase on heating while the simple cubic, f.c.c. and tetragonal phases transform to an h.c.p. structure. The simple cubic and h.c.p. phases correspond to the known high pressure phases of antimony. Films prepared by vapour deposition at room temperature show the same metastable f.c.c. and rhombohedral phases as those observed in splat-quenched foils. Antimony films deposited at liquid air temperatures are amorphous. No metastable structure was observed in lead films quenched from the vapour under similar conditions.

Application of symmetry coupling coefficients in the evaluation of the electronic spectra of d 7 ions

The optical absorption spectrum of cobalt chloride thiourea has been studied at room and liquid air temperatures. The results have been interpreted using group theoretical methods taking into account all the quartet states and several doublet states. Crystal field, electrostatic, and spin-orbit coupling interactions were included to yield the allowed transitions with the relative transition probabilities. The experimental results were interpreted for the following set of parameters: B = 750cm−1, C = 3100cm−1, Δ = 7370cm−1, δ = -200 cm−1, μ = 500cm−1, and ζ = 450 cm−1.

Optical absorption spectrum of nickel fluosilicate hexadeuterate

Optical absorption spectrum of nickel fluosilicate hexadeuterate studied at 300 and 80 K is reported. The splitting of one of the bands at liquid air temperature (80 K) has been explained as due to spin-orbit interaction. Four of the additional bands observed at 80 K have been successfully explained as those belonging to OH and OD molecules. The observed ligand field bands have been interpreted as those of Ni 2+ in octahedral field coupled with a small trigonal field. The crystal field parameters derived are B = 875 cm −1 , C = 3062.5 cm −1 , Dq = 960 cm −1 and ξ = 600 cm −1 .

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 assumingOh symmetry for the Ni2+ ion in the crystal. The fine splitting of the3T11 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.

Lattice vibrations of CdBr2

Very thin samples of CdCl2 type crystals can be produced by stripping with sellotape. This allows the Eu infrared active mode to be observed by infrared absorption at a frequency of 111.5+or-0.5 cm-1 for CdBr2 at liquid air temperatures. This assignment of the Eu infrared mode for CdBr2 is in disagreement with the earlier assignment of Lockwood (1973).

Electronic absorption in silicate mineral of copper

The electronic absorption spectrum of chrysocolla, a silicate mineral of copper, has been studied at room and liquid air temperatures. The observed bands were satisfactorily explained as belonging to Cu2+ ion subjected to tetragonal and spin-orbit fields. A good fit between the theoretical and observed band positions was obtained for the following crystal field parameters:Dq=−1400 cm−1Ds=−3000 cm−1Dt=−800 cm−1λ=−800 cm−1