John C. Woolley

Solid solution, lattice parameter values, and effects of electronegativity in the (Cu1−xAgx)(Ga1−yIny)(Se1−z Tez)2 alloys

Equilibrium conditions for the alloy system (Cu1−xAgx)(Ga1−yIny) (Se1−zTez)2 were determined throughout the complete range of composition. Polycrystalline samples of 125 different compositions, i.e., with x, y, and z=0, 0.25, 0.5, 0.75, and 1.0, were prepared by a melt and anneal technique. Different annealing temperatures in the range 600–800 °C were used depending upon the alloy composition and annealing times of up to 5 months used to attain equilibrium conditions. Debye‐Scherrer x‐ray powder photographs were used to investigate the equilibrium conditions. It was found that single phase chalcopyrite structure was obtained for all compositions of the copper (x=0), indium ( y=1), and tellurium (z=1) sections but that miscibility gaps occurred in the silver (x=1), gallium ( y=0), and selenium (z=0) sections, and that these miscibility gaps extended through the general alloy system. Values of lattice parameters a and c were determined for all samples showing single phase condition and for each of the above...

Low temperature magnetic behaviour of CuFeS2 from neutron diffraction data

Abstract Measurements of neutron diffraction spectra were made at temperatures 4.2, 25, 45, 65, 85, 150 and 300 K on powdered polycrystalline synthetic CuFeS2. Standard Rietveld profile analysis using GSAS showed that at all temperatures, a good fit to the data could be obtained with both the chemical and magnetic space groups taken as I 4 2d, and an antiferromagnetic configuration of the Fe spins, as reported previously by Donnay et al. However, graphs of lattice parameters a and c against temperature showed a distinct change in slope close to 50 K, indicating the presence of a transition. Graphs of integrated intensity of diffraction lines against temperature showed corresponding discontinuities in the case of magnetic and mixed nuclear-magnetic lines but not for nuclear lines, indicating that the transition was magnetic. Detailed calculations of predicted magnetic intensities showed that the intensity variations could be explained by Cu spins, having a paramagnetic arrangement down to 50 K and then ordering to an antiferromagnetic form at lower temperatures. The analysis gave a value of ∼ 0.05 μB for the magnetic moment of the Cu ions.

Miscibility gap in the GaAsy Sb1−y system

Measurements have been made to determine accurately the solidus curve of the pseudobinary section GaAsySb1−y, by annealing samples to equilibrium and determining compositions by x-ray powder photography. It is found that the equilibriui diagram shows a peritectic form with a peritectic temperature of 745 ± 1‡C and a miscibility gap at that temperature extending from y = 0.38 to y = 0.68. It is also shown that as the temperature is lowered the miscibility gap widens rapidly, being from y = 0.30 to y = 0.95 at 700‡C. The form of these phase boundaries is important when growth of GaAsySb1−y alloys by liquid phase epitaxy or similar techniques is considered.

Phase diagram and lattice parameter data for the GaAsySb1−y system

Ingots of GaAsySb1−y alloys have been prepared by various directional freezing techniques, the rate of freezing being kept sufficiently small (e.g. ∼ 0.5cm/day) that equilibrium conditions were obtained in cross-sectional slices. Samples from these slices have then been investigated by powder X-ray photographs and an X-ray fluorescence technique to determine the variation of lattice parameter with composition and the range of single phase solid solution. The results show that this system has a solid miscibility gap of maximum range 0.38 < y < 0.61 and that this corresponds to a peritectic reaction. In the range 0 < y < 0.38 the lattice parameter ao follows the Vegard line, but for 0.61 < y < 1.00 ao lies below this line. By annealing samples in the liquid-solid two phase fields, data have also been obtained on the solidus curve and the peritectic temperature has been shown to be 745 ± 5C.

Temperature effects on the optical energy gap values of CdxZnyMnzTe alloys

Wavelength modulated reflectance measurements were made on a wide range of CdxZnyMnzTe alloys to determine the variation of the energy gap E0 as a function of temperature in the range 10–300 K. It was shown that in the vicinity of the spin‐glass transition temperature Tg, there is a magnetic contribution ΔE which increases E0, and ΔE was determined as the difference between the experimental values and a simple Manoogian–Leclerc extrapolation from higher temperatures. These values of ΔE were fitted to the relation (dt/dt)(ΔE)=−Pt−μ where t=‖T−Tg‖/Tg and good agreement found with the theoretical predictions of Alexander et al. for the effect on the band gap of a critical point such as Tg. As predicted, different behavior was observed close to Tg and at temperatures outside the critical region, μ having a value close to zero in the first range and close to 0.5 in the second. The values of P were very similar for both ranges, extrapolating to zero at the nearest‐neighbor percolation limit of z=0.18 and showin...

Quaternary adamantine selenides and tellurides of the form I III IV VI4

Abstract The preparation of a range of polycrystalline Selenides and Tellurides of the form I III IV VI 4 was undertaken. Twelve Selenides with quaternary composition were prepared but the eight Tellurides attempted did not grow as quaternaries. Single crystal samples of CuGaSnSe 4 were grown by vapour transport. X-Ray powder photography confirmed that the quaternary Selenides have tetragonal Chalcopyrite structure with a c/a ratio of approximately 2. A systematic variation of unit cell volume and of c/a was found over the entire range of compounds grown.

Magnetic properties of CdxZnyMnzTe alloys

Low‐field measurements of magnetic susceptibility χ have been made as a function of temperature in the range 4–150 K on polycrystalline samples of the alloy system CdxZnyMnzTe (x+y+z=1). Values of Tg, the spin‐glass transition temperature, have been obtained from the cusp in the χ vs T curves and values of the Curie‐Weiss θ obtained by extrapolation of the 1/χ vs T line at the higher temperatures. When the various values of Tg vs composition are fitted to a straight line they all extrapolate to a percolation limit of 0.18±0.01. However, it is shown that the plot proposed by Escorne et al. of ln Tg vs az−1/3, where a is the lattice parameter, also gives a straight line variation within the limits of experimental error. This indicates that for z≤0.2, the variation of Tg with z must deviate from linearity. The extrapolated value of 0.18±0.01 is attributed to nearest neighbors only and for z≤0.2 more distant neighbors become relatively more important. For both the Tg vs z and ln Tg vs az−1/3, a change in slop...

Crystallography and optical energy gap values for Cd2x(CuIn)yMn2zTe2 alloys

Abstract Polycrystalline samples of Cd 2 x (CuIn) y Mn 2 z Te 2 ( x + y + z = 1) alloys were prepared by a melt and anneal technique. Debye-Scherrer X-ray powder photographs were used to determine equilibrium conditions and lattice parameter values. It was found that in addition to the zinc blende and chalcopyrite structures, a partially ordered cubic structure was obtained, plus a two-phase field at higher z values. Room-temperature measurements of optical absorption were made to give values of the optical energy gap E g for all single phase samples. It was found that the variation of a was practically linear with composition and so could not be used to determine the boundaries between the three different phase fields. However, while E g varied linearly with composition inside a phase field, the resulting lines had different aiming points at z = 1, the values being 2.83 eV for zinc blende, 1.90 eV for the ordered cubic phase, and 1.36 eV for the chalcopyrite phase. Thus the values of E g give a very good indication of the phase boundaries.

Electron spin resonance in CdxZnyMnzTe alloys

Electron spin resonance (ESR) studies were made on the Mn2+ constituent of CdxZnyMnzTe (x+y+z=1) polycrystalline semimagnetic semiconductors, covering the whole range of solid solutions available, alloys with 0.10≤z≤0.75 being used. These materials exhibit spin‐glass properties at low temperatures. The temperature dependence of the Mn2+ ESR linewidths were measured in the samples between 4.2 to 300 K, and it was found in each case that the linewidth increased with decreasing temperature, reaching a maximum value at a critical temperature Tc. The temperature variation of the linewidths were found to fit a theoretical expression of the form ΔH=A[Tc/(T−Tc)]α, where ΔH is the linewidth, A is a constant, Tc is the critical temperature and α is the critical exponent. The percolation limit for any ratio of x:y was found to be in the range 0.20≤z≤0.25. For values of z above this limit, Tc was found to vary smoothly with z for fixed x:y ratios, showing a linear variation in the limiting case of Zn1−zMnzTe , and al...

Effects of crystallographic ordering on the magnetic behaviour of (AgIn)1-zMn2zTe2 and (CuIn)1-zMn2zTe2 alloys

Abstract Measurements of magnetic susceptibility in the temperature range 4.2–300 K were made on polycrystalline samples of the (AgIn) 1 - z Mn 2 z Te 2 and (CuIn) 1 - z Mn 2 z Te 2 alloys, and the data used to give values of spin-glass transition te mperature T g and Curie-Weiss paramagnetic temperature θ. For any sample for which the X-ray powder photograph indicated an apparently single phase condition, either zinc-blende or chalcopyrite, the susceptibility data could show up to three separate T g values. These different magnetic conditions are attributed to crystallographic ordering of the Mn ions on the chalcopyrite and zinc-blende lattices, the three observed T g values corresponding to disordered zinc-blende, ordered zinc-blende and ordered chalcopyrite. The value of θ obtained from the 1/χ vs. T plot is shown to be a weighted mean of the separate values of θ for the phases present. The relative sizes of the T g peaks and the values of θ for any given sample gives an indication of the amount of each phase present. These amounts were varied by using different methods of heat treatment and it was shown that the magnetic behaviour was consistent with the T ( z ) phase diagram for the two alloy systems.