Defect dominated conductivity in Zn3P2

The electrical resistivity and Hall coefficient of Zn₃P₂ have been measured for single crystal and thin polycrystalline film samples which were annealed over a range of equilibrium vapor compositions and temperatures. The room temperature electrical resistivity of single crystal samples annealed at 573 K varied from approximately 10⁵Ω-cm for single crystals heated in equilibrium with zinc to 10 Ω-cm for those annealed in a phosphorus rich ambient. Hall measurements indicate that a variation in carrier concentration is responsible for these changes. The experimentally observed dependence of carrier concentration [h° ], (cm^?3) on phosphorus pressure is given by [h°] = 1.32 · 10¹⁶ [p(P₄)]^0.13 for samples annealed at 573 K. The experimentally determined pressure dependence is in good agreement with a model based on phosphorus interstitials acting as acceptors. The pressure and temperature dependence of the carrier concentration yield the equilibrium constant K_I for the formation of interstitial phosphorus defects according to the reaction

$\text{1}\text{4}\text{P}{}_4\text{→ P′}{}_{\mathrm{i}}\text{+ h°}$

where

$\text{K}{}_{\mathrm{I}}\text{= 10}{}^{\mathrm{42.4\; \pm \; 2}}\text{cm}{}^{\mathrm{?6}}\text{torr}{}^{0.25}\text{[p(P}{}_4\text{)]}{}^{\mathrm{?0.25}}\text{exp(?1.18}\text{ev}\text{kT}\text{)}$

. The accommodation of phosphorus interstitials is discussed in light of the crystal structure of Zn₃P₂.     

A piezomodulation study of the absorption edge and Mn++ internal transition in Cd1−xMnxTe,a prototype of diluted magnetic semiconductors

We report the first piezomodulation spectrum of Cd_1?xMn_xTe. Signatures of the exciton transition and the internal transition of Mn⁺⁺ are identified. The opposite signs of these signatures are attributed to the positive pressure coefficient of the direct interband transition as contrasted to a negative pressure coefficient for the ${}^6\text{A}{}_1\text{→}{}^4\text{T}{}_1$ transition causing the Mn⁺⁺ feature.     

Impurity-assisted intervalley scattering in uniaxially stressed silicon

F-type intervalley scattering in stressed silicon is studied by means of photoluminescence from “hot” and “cold” electron-hole drops and free excitons. The scattering rates are shown to be essentially determined by the impurity concentration before TA-phonons initiate complete thermalization among the electrons in the up- and down-shifted conduction valleys. For phosphorus donors, scattering probabilities of ? 2x10^?6$\text{cm}{}^3\text{sec}$ are obtained. Much lower scattering probabilities are found for boron acceptors.     

High resolution spectroscopy using photodeflection

Isotope separation by laser deflection of an atomic beam, combined with simultaneous mass spectroscopy, has been used to determine optical frequency shifts and to assign mass numbers to all components of the $\text{Ba 6s}{}^2{}^1\text{S}{}_0\text{?6s6p}{}^1\text{P}{}_1$ 5536 Å resonance. Several components which cannot be resolved optically without the use of enriched samples, were resolved with the technique described. They are ${}^{135}\text{Ba}\text{(F=}\text{5}\text{2}\text{)}$ at 120 MHz, ¹³⁶Ba at 128 MHz and ¹³⁴Ba at 138 MHz.     

N2+ bound quartet and sextet state potential energy curves

Potential energy curves for the ${}^4\text{Σ}{}^{\mathrm{+}}{}_{\mathrm{u}}$, ${}^4\text{Π}{}_{\mathrm{g}}$ and ${}^6\text{Σ}{}^{\mathrm{+}}{}_{\mathrm{g}}$ states of N⁺₂ that dissociate to N (${}^4\text{S}{}^0$) and $\text{N}{}^{\mathrm{+}}\text{(}{}^3\text{P)}$, have been determined from a complete active space self-consistent field calculation. The ${}^6\text{Σ}{}^{\mathrm{+}}{}_{\mathrm{g}}$ state is found to be significantly bound (D_e = 2.68 eV) with a minimum at 1.72 Å.     

A new organic low temperature conductor: HMTSF-TNAP

Conductivity and optical data on a new organic, conducting charge transfer salt Δ^{2, 2′}-Bi-(4,5-trimethylene-1,3-diselenole) 11,11′,12,12′-tetracyano-2, 6-napthoquinodimethane (HMTSF-TNAP) are given. $\text{σ(300}\text{K}\text{)= 2400 ± 600 Ω}{}^{-1}\text{cm}{}^{-1}$. A maximum in σ(T) is found at T_M = 47 K with σ(T_M)/σ(300 K) = 6.0 ± 10%, and $\text{σ(1.5}\text{K}\text{) > 250 Ω}{}^{-1}$. σ(T) is well defined in the high temperature region, but is sample dependent at low temperatures. The optical data indicate a bandwidth and carrier density comparable to that of HMTSF-TCNQ.     

Determination of the fermi surface of monoclinic SrAs3 by Shubnikov dehaas effect

The electronic properties of single crystals of monoclinic SrAs₃ have been studied by investigating the temperature dependence of electrical conductivity, Hall effect and Shubnikov de Haas (SdH) oscillations. At 4.2 K, SrAs₃ is predominantly p-conducting with a typical hole concentration of 6 × 10¹⁷cm^-3. The Hall coefficient changes its sign near 80 K. The angular dependence of the SdH oscillations was used to map out the shape of the Fermi-surface of holes. Two asymmetric, quasi-ellipsoidal Fermi-bodies are located in the first Brillouin zone. The cyclotron effective masses $\text{m}{}^1$ for two crystallographic directions were calculated from the temperature dependence of the amplitude of the oscillations: $\text{m}{}^1\text{(B6a)=(0.70± 0.002)m}{}_0$and $\text{m}{}^1\text{(B6c}{}^1\text{)=(0.095±0.003)m}{}_0$, respectively. There are indications for a third Fermi-surface which is attributed to electrons.     

Electrical conductivity of LiNbWO6

The electrical conductivity of polycrystalline LiNbWO₆, which has a trirutile structure, was studied by the ac impedance method and dc resistance measurement. From the results, the following is clear; LiNbWO₆ is a lithium ionic conductor, its electrical conductivity at 150°C is $\text{1.8 × 10}{}^{\mathrm{?6}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ and the electronic transference number is about 0.03.     

Kerr-effect and dielectric tensor elements of magnetite (Fe3O4) between 0.5 and 4.3 eV

The complex polar Kerr effect (rotation and ellipticity) of magnetite single crystals has been measured at room temperature between 0.5 and 4.3 eV. From the magneto-optical data and the optical constants, the off-diagonal elements (?_xy) of the dielectric tensor has been derived. Three well separated magneto-optical transitions have been indentified. At about 0.75 eV one strong magneto-optical structure with a diamagnetic line shape is assigned to a $\text{3d}{}^6\text{→3d}{}^5\text{(}{}^6\text{A}{}_{\mathrm{1g}}\text{) 4s}$ transition from Fe²⁺ in octahedral sites. Two other structures with paramagnetic line shapes near 1.85 and 2.90 eV are assigned to the orbital promotion processes $\text{3d}{}^6\text{(Fe}{}^{\mathrm{2+}}{}_{\mathrm{oct}}\text{)→3d}{}^5\text{(}{}^4\text{T}{}_{\mathrm{1g}}\text{) 4s}$ and $\text{3d}{}^5\text{(Fe}{}^{\mathrm{3+}}{}_{\mathrm{tet}}\text{)→3d}{}^4\text{(}{}^5\text{T}{}_2\text{) 4s}$, respectively, which take into account Fe 3d^n?1 final state effects.     

Chemical diffusion in nonstoichiometric chromium sulfide,Cr2+yS3

Using the re-equilibration kinetic method the chemical diffusion coefficient in nonstoichiometric chromium sesquisulfide, Cr_2+yS₃, has been determined as a function of temperature (1073–1373 K) and sulphur vapour pressure (10?10⁴ Pa). It has been found that this coefficient is independent of sulphur pressure and can be described by the following empirical equation: $\text{D}\text{?}\text{Cr}{}_{\mathrm{2+y}}\text{S}{}_3\text{=50.86}\text{exp(-39070 cal/mole/}\text{RT)}\text{(cm}{}^2\text{s}{}^{\mathrm{?1)}}$. It has been shown that the mobility of the point defects inCr_2+yS₃ is independent of their concentration and that the self-diffusion coefficient of chromium in this sulfide has the following function of temperature and sulphur pressure: . (cm²s^?1).     

Dye laser site selection spectroscopy on U6+ luminescent molecular centers in LiF-U3O8 crystals

The polarized excitation and emission spectra of the U⁶⁺ molecular centers giving the most intense emission lines at 18 940 cm^?1 and 19 285 cm^?1 are presented and analyzed in detáil. From the polarization experiments, it is shown that the symmetry of the centers is C_4v and that the symmetries of the observed electronic states are Γ₂, Γ₁ and Γ₅. Finally, an electronic model is proposed which associates the emission and excitation lines of the U⁶⁺ centers in the visible region to transitions between the fundamental state $\text{Γ}{}_1\text{(6p}{}^6\text{,}{}^1\text{S)}$ and the states of the excited configuration $\text{6p}{}^5\text{(}{}^2\text{P}\text{3}\text{2}\text{) 7s}$.     

Rotation-vibration analysis of the Coriolis-coupled ν5g, ν6g, ν8g and ν9 bands of H2CCO

Medium resolution infrared grating spectra of gaseous ketene, H₂CCO were recorded between 1000 and 400 cm^?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm^?1 between 450 and 330 cm^?1. The K structure of the fundamentals ν₅, ν₆, ν₈, and ν₉ was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are $\text{ν}{}_5{}^0\text{= 587.30 (27)}$ and $\text{ν}{}_6{}^0\text{= 528.36 (39)}\text{cm}{}^{\mathrm{?1}}$. Synthetic spectra indicate the band origins of ν₈ and ν₉ to be close to 977.8 and 439.0 cm^?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are $\text{ζ}{}_{58}{}^{\mathrm{a}}\text{= + 0.33 (5)}$, $\text{ζ}{}_{68}{}^{\mathrm{a}}\text{= + 0.714 (20)}$, $\text{ζ}{}_{59}{}^{\mathrm{a}}\text{= ? 0.774 (20)}$, and $\text{ζ}{}_{69}{}^{\mathrm{a}}\text{= ? 0.30 (2)}$. Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are $\text{M}{}_8{}^0\text{:±iM}{}_5{}^0\text{:±iM}{}_6{}^0\text{:M}{}_9{}^0\text{≈ +2:?9:+10:+0.5}$.     

A study of valency changes of vanadium ions in Al2O3 by γ irradiation

The effect of γ irradiation at 300 K on the concentrations of vanadium ions V³⁺, V⁴⁺ and V²⁺ in Al₂O₃ has been studied quantitatively, using three techniques: optical absorption (V³⁺), low temperature thermal conductivity measurements (V⁴⁺) and EPR (V²⁺). Several single crystals of Al₂O₃ doped with vanadium in a large range of concentration $\text{(2.8 × 10}{}^{18}\text{? 1.3 × 10}{}^{20}\text{at.}\text{cm}{}^3\text{)}$ have been measured. The evolution of the respective concentrations by γ irradiation as a function of the total vanadium content C is quite different in the two regions $\text{C< 1.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ and C larger than this value. A consistent analysis of the results has nevertheless been achieved, leading to the determination of the absolute concentrations of the three ions in the as-received and γ irradiated states for all samples with $\text{C<4.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ (room temperature annealing is observed above this value). The concentrations of V⁴⁺ and V²⁺ ions are always small, but V⁴⁺ ions are more stable: they are present in the as-received state at a level of 1% of the total concentration and a maximum value of $\text{/}\text{?}\text{2.3 × 10}{}^{18}\text{at.}\text{cm}{}^3$ is observed in the γ irradiated state; on the other hand there are less than 4.7 × 10¹⁵V²⁺ ions per cm³ in the as-received state and the maximum value is only $\text{4.2 × 10}{}^{17}\text{at.}\text{cm}{}^3$. Charge transfer between V ions only is not sufficient to explain the experimental results and other defects must be involved in the γ irradiation effect.     

Stark mixing spectroscopy in cesium

We present a new technique for selectively populating excited states which are inaccessible by dipole excitation from the ground state. The method uses a static electric field to introduce a component of a dipole-allowed state into the state of interest. We have applied the method to cesium to measure lifetimes and a Stark mixing coefficient. The results are $\text{τ(6}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=64(2) ns}$, $\text{τ(7}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=92.5(15) ns}$, and <6²D_{$\text{5}\text{2}$}|;ez |7²P_{$\text{3}\text{2}$}>/(E_7P?E_6D)=0.7(3)×10^?3 where is in kV/cm. 141     

A study of 3He capture in light nuclei

Excitation functions at θ = 90° have been measured for ${}^{16}\text{O}\text{(}{}^3\text{He}\text{, γ}{}_{\mathrm{0?2,\; 3?5,\; 6}}\text{)}{}^{19}\text{Ne}$, ${}^{15}\text{N}\text{(}{}^3\text{He}\text{, γ}{}_{\mathrm{0,\; 1?4}}\text{)}{}^{18}\text{F}\text{,}{}^{14}\text{N}\text{(}{}^3\text{He}\text{, γ}{}_{\mathrm{0,\; 1,2,3}}\text{)}{}^{17}\text{F}$, and ${}^{20}\text{Ne}\text{(}{}^3\text{He}\text{, γ}{}_{\mathrm{0\; +\; 1}}\text{)}{}^{23}\text{Mg}$, in the range E_{3He = 3–19 MeV}. The first reaction has also been studied at θ = 40°. Excitation functions at 90° have also been measured for and ${}^4\text{He}\text{(}{}^3\text{He}\text{, γ}{}_{\mathrm{0\; +\; 1}}\text{)}{}^7\text{Be}$ for E_3He = 19–26 MeV. Angular distributions have been measured for the first four reactions.For the most excitation functions, a broad peak is observed, several MeV wide, centred at about E_x≈ 20 MeV. Superimposed on this, in some cases, are narrower peaks, with width ≈ 1 MeV. Energies and widths have been extracted for all resonances.Cluster-model calculations have been carried out, using methods similar to those which have proved successful for low-lying states in A= 18–19 nuclei. No satisfactory correspondence with the present results was found. The shell model has been used to calculate Γ_3He and Γ_γ for 1?ω excitations in the final nuclei. These generally show good agreement with the trends of the experimental data. The results are consistent with the excitation of the giant dipole resonance in ³He capture, but much more weakly than in proton capture.     

Ni2+ emission in MgO,KMgF3, KZnF3 and MgF2

The emission of Ni²⁺ ions in MgO, KMgF₃, KZnF₃ and MgF₂ crystals has been investigated. The fine structure on the bands at about 20 000 cm^-1 and 13 000 cm^-1 has been studied in detail and from this and the excitation spectra these bands are assigned to ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{A}{}_{\mathrm{2g}}$ and ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{T}{}_{\mathrm{2g}}$ transitions respectively.     

Nuclear moments and optical isotope shift of radioactive 133Ba

Mass separated radioactive ¹³³Ba has been investigated by means of optical spectroscopy. From hyperfine structure and isotope shift we obtain the nuclear magnetic moment μ_I = ?0.769(3) μ_n and the change of the nuclear mean square charge radius $\text{δ〈r}{}^2\text{〉 (}{}^{133}\text{Ba}\text{?}{}^{132}\text{Ba}\text{) = ?0.017(3)}\text{fm}{}^2$.     

Absolute vacuum ultraviolet absorption spectra of some gaseous azabenzenes

Absolute extinction coefficient and oscillator strength of pyridine, pyrimidine, pyrazine, and s-triazine were recorded with moderate resolution in the region of 3.5–9.5 eV. Analogous to ${}^1\text{A}{}_{\mathrm{<mtext>1</mtext><mtext>g</mtext>}}\text{→}{}^1\text{B}{}_{\mathrm{<mtext>2</mtext><mtext>u</mtext>}}$, ¹B_1u, ${}^1\text{E}{}_{\mathrm{<mtext>1</mtext><mtext>u</mtext>}}\text{π → π}{}^1$ transitions of benzene, several $\text{n → π}{}^1$ and Rydberg transitions are presented and discussed.     

Thermal vibration in the cubic phase of K2SnCl6

The rectilinear and angular mean-square displacements of the atoms in K₂SnCl₆ have been measured from 293 to 450 K using single-crystal X-ray diffraction. The motion of the tin and chlorine atoms has been found to consist, essentially, of rigid-body translation and libration of the SnCl₆ octahedra. The root-mean-square angle of libration of the SnCl₆ octahedra, $\text{φ}{}^2$^{$\text{1}\text{2}$}, ranged from 5.7 to 6.1°. The slow variation of $\text{φ}{}^2$ with temperature, together with the measured non-zero value of one of the fourth cumulants of the chlorine atom displacement, are indicative of highly non-linear coupled motion associated with the soft-mode phase transition at 261.5 K.     

Charge transport in layer semiconductors

Electron and hole-drift velocity is measured in the layer semiconductors HgI₂, GaSe, PbI₂ and GaS, mainly on the direction parallel to the c-axis between 80 and 400 K. In the electric field range in question, electron and hole-drift velocity is proportional to the field except in the case of GaS, where a superohmic behaviour is observed. At 300 K the mobility parallel to the c-axis is $\text{μ}{}_{\mathrm{e}}\text{, = 100}\text{cm}{}^2\text{Vsec}$, $\text{μ}{}_{\mathrm{h}}\text{= 4}\text{cm}{}^2\text{Vsec}$ for HgI₂; $\text{μ}{}_{\mathrm{e}}\text{= 80}\text{cm}{}^2\text{Vsec}$, $\text{μ}{}_{\mathrm{h}}\text{= 210}\text{cm}{}^2\text{Vsec}$ for GaSe; $\text{μ}{}_{\mathrm{e}}\text{, = 8}\text{cm}{}^2\text{Vsec}$, $\text{μ}{}_{\mathrm{h}}\text{= 2}\text{cm}{}^2\text{Vsec}$ for PbI₂. The highest hole mobility observed in GaS is $\text{μ}{}_{\mathrm{h}}\text{= 80}\text{cm}{}^2\text{Vsec}$.Where it is possible to compare these data with mobility values perpendicular to the c-axis, the three-dimensional character of the energy bands near the fundamental gap is proved.For HgI₂ and GaSe we find no evidence for the large anisotropy of charge-carrier transport properties usually attributed to layered semiconductors. The mobility-temperature dependences found are interpreted on the basis of polar and non-polar optical phonon scattering mechanisms, except in the case of GaS, where a trapping model is used. The effective masses of electrons and holes are reported for PbI₂ and, for the first time, for HgI₂.