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The transient characteristics of the dark current have been measured in SbI3‐doped HgI2 single crystals as a function of voltage and temperature for different dopant concentrations. The doping by Sb3+ was found to introduce a hole trapping level 0.5‐eV deep, with a density which was of the same order of magnitude as the SbI3 content. The room‐temperature effective hole mobility was 5×10−8 cm2/V s for 1.5 wt.% dopant content, as compared to about 2×10−6 cm2/V s for 0.1 wt.% dopant content. Previous results obtained with undoped crystals showed an effective mobility of 5×10−7 cm2/V s, but the trap depth was different, 0.7 eV, and the concentration was much lower, only of the order of 1015 cm−3.

Measurement results obtained with HgI2 detectors at room temperature in the low energy x-ray region down to 2 keV are reported. The best resolution obtained is 548 e V for 5.9 keV x-rays, and the 2.01 keV phosphorous x-ray line has been resolved with a detector with an area of 14 mm2. The different noise sources of the detector-amplifier system are analysed and polarization effects in the detectors are discussed. The mercuric iodide crystals were grown from the vapour phase by gradient reversal techniques.

Crystals of HgI 2 are grown from the vapor phase using the Temperature Oscillation Method. Techniques to dope the crystals with Hg, I 2 , NH 4 I, SbI 3 , PbI 2 , and TeI 4 during growth are described. Evaluation of the external morphology indicates that HgI 2 can incorporate a relatively large excess of Hg. Increasing the iodine concentration in the crystals introduces morphological break- down of the vapor/solid interface.

We have explored the merits of using a Hgl2 spectrometer as a detector in x-ray diffraction systems instead of a proportional gas counter, or a scintillation counter. The full width at half maximum energy resolution of the HgI2 spectrometer used was about 1.1 keV for the CuKα line (8.1 keV), and about 1.5 keV for the MoKα line (17.4 keV), The energy resolution was utilised to eliminate x-ray fluorescence background from powder diffraction spectra. We demonstrate the suppression of Fe x-ray fluorescence in diffraction patterns of ErFe03 obtained with a Cu x-ray tube, and of Y x-ray fluorescence in diffraction patterns of Y2O3 obtained with a Mo x-ray tube. The peak height to background ratios were improved by about an order of magnitude in both cases.

The occurrence of deviations from stoichiometry of the semi-insulator compound HgI2 has been established using a very elaborate chemical analytical procedure. It was found that the molar ratio of I 2 Hg varies from 1.993 to 2.015 (±0.002). The deviations from stoichiometry have been corroborated by studying the red to yellow solid state phase transformation temperature. It was found that the compounds, whether rich or poor in iodine, have lower Ttr than those closest to stoichiometry, i.e., where the I 2 Hg ratio is 2.000.

Mercuric iodide single crystals have been grown by static and dynamic sublimation methods. Characteristics of contacts and detector capacitance have been studied by photon excitation methods. Gamma and X-ray spectrometry has been carried out with completed detectors showing resolutions comparable to the best results published to date. A measurement of hole trapping length has been made from the spectral shapes observed and has been found to be approximately 0.3 mm. Transient waveform analysis with alpha-particle excitation shows hole mobilities of approximately 3 cm2/V-sec for a highly purified crystal and 0.05 for an expected less pure crystal. Electron mobilities of 120 cm2/V-sec are observed. An attempt is made to explain the observed transient waveforms in terms of a single dominant trap model, with only partial success. Due to the strongly excitonic character of the material, it is proposed that the unfamiliar observations made regarding transport properties with the HgI2 detectors studied may be due to exciton dissociation under high electric fields, to long exciton lifetimes and to interactions between excitons and trapping centers in the material.

A comparative study of the purification of α-HgI 2 by zone refining, solvent extraction, and the more effective repeated sublimation method is reported. Detector quality crystals have been grown using initially-purified raw materials by either a static or dynamic pulling vapor-growth or solution-growth method. The latter involves solvent evaporation or slow cooling of saturated solutions in CH 3 I, CH 3 OH, and CH 2 I 2 or by decomplexing solutions containing HgI 3 - for which phase diagrams have been established. X-ray topographical studies indicate that purity rather than physical perfection is the primary requirement for a detector crystal. The gamma-ray spectra of 241 Am, detected at room temperature with static and dynamically pulled vapor- and solution-grown HgI 2 crystals, are also reported.

Rare earth iron silicides and germanides of the R Fe 2 Si 2 or R Fe 2 Ge 2 type with R = La, Ce, Pr, Nd, Sm, Gd and Dy were measured for their magnetic susceptibility. The silicides and germanides of Nd and Gd are antiferromagnetically ordered below a Neel point of, respectively, 11 and 7°K for the silicides and 13 and 11 for the germanides. The Nd sublattice under-goes a spin-flop transition which at 4.2°K is at 11 KOe. Although the Fe sublattice is diamagnetic, all the samples showed a weak ferromagnetic ordering below a temperature of about 700°K. The ratio between the dia- and ferromagnetic phases is 94:6 per cent in the silicides and 80:20 in the germanides, as determined by Mossbauer spectroscopy and supported by magnetization measurements.

Miniature mercuric iodide nuclear detectors which are cased in either a larger 6 mm or smaller 1.7 mm outer diameter probes for potential use as gamma medical probe detectors have been fabricated and tested. The larger probes have been used mainly to monitor the dc output produced by high fluxes of 40 keV X-rays or of a 10 mCi a 226 Ra source which 15 mm long and which was placed at distances of 1–10 cm from the HgI 2 probe. The smaller probe, encased in a 16 gauge syringe needle was used mainly in the counting mode and resolved the 28 and 35 keV photopeak of 125 I. The nuclear response of the tiny planar detector encased in the needle probe is anisotropic in the ratios of about 1.4:1.0 and 1.2:1.0 for monitoring 60 and 122 keV gamma rays perpendicular or parallel to the detector contact area respectively.

Transient characteristics of dark currents have been measured in HgI2 single crystals as functions of voltage and temperature. The existence of a hole trapping center, 0.7 eV deep and of density ∼1015 cm−3, was established, which effectively lowers the hole drift mobility by about seven orders of magnitude. The samples were found to be slightly extrinsic n type, the Fermi level being 0.9 eV deep. The room‐temperature electron density was about 2×103 cm−3. The meaning of these characteristics to the performances of HgI2 γ‐ and x‐ray spectrometers is discussed. Particularly, it is suggested that lowering of the HgI2 detector operation temperature to about 0 °C will improve its energy resolution capabilities.

A new device has been designed to facilitate the cleaving of thin sections from bulk crystals of mercuric iodide. Crystallographic perfection of the machine-cleaved sections was established by gamma-ray diffraction rocking curves and was found to be higher than the perfection of hand-cleaved sections or of as-grown thin platelets, approaching the perfection of string-sawn sections of HgI/sub 2/. A correlation was found between the perfection and thickness of the machine-cleaved sections, i.e., the thicker the section the more perfect it is. Reproducibility of the fabrication was significantly improved by using machine cleaving in the fabrication process.

Pyrolysis of alkyl silane on silicon or tungsten substrates produces SiC films contaminated by various amounts of carbon and silicon. Under the same conditions of pyrolysis but using polycrystalline quartz substrate, the resultant deposit consists of hollow whiskers of silicon as characterized by transmission electron diffractions.

Total organic carbon was determined by measuring the CO 2 produced by combustion in a sealed quartz vessel. The CO 2 was quantified by nondispersive IR and by titration using commercial detectors. The total organic carbon was found to be around 10–100 μg/g in both starting materials and in single crystals. Gas chromatography-mass spectroscopy (GC/MS) measurements were made on hexane extracts of mercuric iodide (HgI 2 ) dissolved in potassium iodide solution. Hydrocarbons starting with C 10 (DIENE) and up to C 26 were found. In addition, phthalates, such as diethyl and dioctyl phthalate were also found. Some of the organic compounds, for example, such hydrocarbons as branched nC 16 , nC 20 , nC 21 , nC 22 , nC 23 , and nC 24 , were present in some HgI 2 materials in quantities of the order of weight ppm, but were eliminated in the purification process and were not found in the single crystals. Other organic compounds such as the phthalates were not always eliminated and were identified in the single crystals. In general, the GC/MS could identify only hydrocarbons of C 10 and higher which account for only a few percent of the total organic carbon determined by oxidation.

Methods of material purification and crystal growth of mercuric iodide (HgI 2 ), plus preparation and characterization of nuclear detectors fabricated from HgI 2 crystals, are reviewed. The state of the art of HgI 2 nuclear detector fabrication is assessed. The use of HgI 2 to detect low energy X-rays of about 1.5 keV and its potential use for high energy gamma-ray detection of up to 1332 keV, as seen from 137 Cs and 60 Co gamma spectra, are discussed.

The Modified Entrainment Method (MEM) was used to compare the vapor pressures of HgI 2 from different sources in the temperature range 100–200°C. The vapor pressure varied with the impurity content and the stoichiometry of the materials studied. Impure or nonstoichiometric HgI 2 samples were found to have vapor pressures higher than those of purified and more nearly stoichiometric materials. The MEM was used here for the first time to observe a phase transition: red to yellow HgI 2 .

A study of the performance of currently available CdTe and Hgl2 detectors has been undertaken in the 10-660 keV energy range, in order to evaluate the possibilities as well as the limitations of these spectrometers. Energy resolution, absolute photo-peak efficiency, total counting efficiency, the ratio between the photopeak and total counts and risetime distributions have been successively analyzed.

Both space-charge-limited current and space-charge-free current pulses for electron and hole injection in HgI2 crystals have been observed using the Pulsed Laser Transient Charge Technique. A semi-quantitative theoretical analysis is made based on the assumption of a semi-insulating material. The current pulse analysis includes trapping, detrapping, field dependent trapping times (in both space charge free and limited cases), and plasma dispersal times. Measurement of trapping times and mobilities for both types of carriers are made from the pulse shapes. Measured values for the mobilities of both electrons and holes and trapping times are comparable to previous measurements using different techniques. The experimental techniques are also described. Lastly, the crystal growing techniques are outlined.

Dimethylsulfoxide is found to be an effective solvent for solution growth of large mercuric iodide crystals. Solvent properties, crystal growth and characterization, and nuclear detector properties are dis-cussed. When tested as nuclear radiation detectors, solution-grown crystals did not function as well as vapor-grown crystals.

The purification procedure of the LiY 0.5 Er 0.5 F 4 compound for Bridgman-Stockbarger and Czochralski single crystal growth has been investigated. Yttrium and rare-earth oxyfluorides were found to form during hydrofluoric heat-treatment of the starting fluoride mixture. Optically clear single crystals of purified LiY 0.5 Er 0.5 F 4 were grown by both Bridgman-Stockbarger and Czochralski methods. The stoichiometry was investigated by magnetic susceptibility measurements and the Er content in the single crystals grown by both Bridgman-Stockbarger and Czochralski methods were found to fit stoichiometry within the measurement error. No free (OH) − ions were found by infrared absorption spectroscopy.

Silicon-containing coatings were deposited on the nickel-based superalloy Hastelloy-X using the chemical vapour deposition technique. The coatings were obtained from gas mixtures of SiCl4H2 and SiCl4N2H2. The molar ratio of the SiCl4 was 5 × 10−3 mol l−1 in a total flow of 3 l min−1 at atmospheric pressure through a 50 mm diameter reactor. The N2:H2 ratio was 3:1. The substrates were heated to the temperature range 850–1100 °C on a graphite susceptor by an r.f. generator at 380 kHz. The coatings obtained in the temperature range 900–1000 °C consisted of two layers. X-ray diffraction revealed the existence of the following silicide phases in the coatings: NiSi, Ni3Si, Ni16(Cr,Ti)6Si7 (G phase). No pure silicon was found on the coatings.

The yield of HgI2 vapor grown platelets in the presence of polythylene is reported here for the first time to be dependent on the ampoule geometry. The quality of the HgI2 platelets was characterized in terms of each pit density, traping time, surface recombination velocity and spectral response using X- and γ-ray spectrometers. The above parameters were measured for HgI2 platelets and compared with the Temperature Oscillation Method (TOM) grown bulk HgI2 crystals.

The standard procedure used in our laboratory to purify commercially available mercuric iodide (HgI2) consists of a sequence of steps: (1) repeated sublimation under continuous evacuation, followed by (2) melting and recrystallization, and (3) a sublimation process in a closed tube. This paper describes a modification of the standard purification sequence by adding recrystallization of the HgI2 in hydrochloric acid. Leaching cation impurities out of HgI2 powder with hydrochloric acid has been practised before by Zaletin et al. Our objective for the hydrochloric acid treatment was to remove nitrates and hydrocarbons which were interfering with the vapor transport during crystal growth. Results of the procedure are presented in terms of total carbon and selected ion content of the treated and untreated material.

Nuclear detectors of HgI2 exposed to high fluences of up to 40 keV x-rays of counting rates up to 1012 photons sec-1 cm-2 which correspond to about 400 R/min show linear dependence of the dc current of the detector with the x-ray dose. Polarization can cause the deterioration of the dc current within the detector with a decay time which varies from several seconds to several hours at the highest fluence after which the dc current reaches a steady value. Better crystals, however, show practically no time deterioration of the dc current. The dc response of HgI2 nuclear detectors to high fluences of x-ray pulses of several milliseconds duration was also measured. Both the rise times and decay times varied between 0.4 to 0.8 millisecond for uncollimated and 0.06 to 0.3 millisecond for collimated x-rays.

High-temperature studies of mercuric iodide (HgI/sub 2/) involving differential scanning calorimetry (DSC), Raman spectroscopy, and x- ray powder diffraction have failed to confirm the existence of a red-colored tetragonal high-temperature phase called ..cap alpha.. '-HgI/sub 2/ reported by S.N. Toubektsis et al., (S.N. Toubektsis, E.K. Polychroniadis, and N.A. Economou, J. Appl. Phys., 58(5) (1985) 2070), using DSC measurements. The multiple DSC peaks near melting reported by Toubektsis are found by the present authors only if the sample is heated in a stainless-steel container. Using a Pyrex container or inserting a platinum foil between the HgI/sub 2/ and the stainless-steel container yields only one sharp, single DSC peak at the melting point. The nonexistence of the ..cap alpha..' phase is confirmed by high- temperature x-ray diffraction and Raman spectroscopy performed in the vicinity of the melting point which clearly indicate the existence of the yellow orthorhombic ..beta..-HgI/sub 2/ phase only. The experimental high-temperature DSC, Raman, and x-ray diffraction data are presented and discussed. 14 refs., 8 figs., 2 tabs.

The use of the Transient Charge Technique (TCT) for the evaluation of high resistivity Mercuric Iodide and Cadmium Selenide nuclear radiation detectors is suggested. It has been shown that the real values of mobilities and trapping times of electrons and holes in HgI2 can be easily obtained from the analysis of the voltage transient response to drift of charge carriers created by alpha particles. This allows to evaluate the bulk transport properties of the material and, additionally, to estimate accurately the surface recombination velocity of the carriers. Preliminary results on the shape of voltage transients in CdSe are also reported, and the limitations of the use of the TCT for characterisation of both materials are discussed.

HfO 2 films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 A) nearly stoichiometric monoclinic HfO 2 . The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO 2 films varied between 2 × 10 6 and 4.5 × 10 6 V cm −1 . C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10 11 and 6 × 10 11 cm t−2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V FB values were between −0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V 2 over a wide range.

The procedure of preparing starting materials of HgI 2 pre-treated with iodine and crystal growth from the vapor phase using the temperature oscillation method, TOM, in both a horizontal and vertical furnace is reviewed. The nuclear radiation detector properties of two of the best representative crystals grown in a horizontal furnace from iodized material and in a vertical furnace from non-iodized material are shown and discussed. The smallest full width half-maximum, fwhm, so far detected with a 10×8×0.5 mm 3 mercuric iodide detector is 4.5 keV for the 662 keV photopeak of 137 Cs.

The feasibility of NaI(Tl) scintillators replacement by high energy resolution HgI2 detectors for rCBF measurements based on 133Xe inhalation technique has been investigated. Exhaustive phantom mapping has been carried out using 133Xe quasi-point sources. Comparative clinical rCBF measurements have been performed using the HgI2 and NaI(Tl) detectors simulaneously. The results show that the superior energy resolution of HgI2 compared to the NaI(Tl) and commercially available CdTe detectors allow efficient energy rejection of the scattered radiation, which improves considerably the spatial resolution of the rCBF instrumentation.

Tiny nuclear detector mercuric iodide probes which fit into a syringe needle of 0.9 mm diameter have been fabricated. Spectroscopic evaluation of the nuclear response shows im roved energy resolution of less than 10% for 57Co and 241Am. The probes show long term stability. One of the still unsolved problems of these probes is the lower energy anisotropic spatial response. Single sources of 137Cs and 125I were placed in a water phantom and counted with the probes. Calibration of the probes against the calculated dose rates for these sources, was carried out, and plotted.

The influence of various fabrication parameters on the surface quality of HgI2 X-ray spectrometers has been studied in detail. Exposure of etched HgI2 to ambient atmosphere for ∼ 24 h may reduce the electron surface recombination velocity by almost an order of magnitude. Reduction of the etching solution temperature (KI in water) to about 0°C and an increase of the KI concentration to ∼ 20 wt% are also important.

The majority of HgI2 detectors which have an energy resolution less than 5% for 241Am do not have severe plarization effects at all. Polarization effects are reported for detectors having energy resolution greater than 5% for 241Am in an attempt to discover if polarization is mainly due to either a nonoptimal fabrication or to severe trapping in the bulk crystalline material. An improved fabrication procedure using a rapid etch and evaporated palladium contacts is reported. This procedure has produced polarization free detectors which were refabricated from detectors which previously showed polarization.

Crystals of HgI 2 prepared from purified and iodine treated starting material and grown from the vapor phase in an improved horizontal furnace using the temperature oscillation method, TOM, have resulted in better quality crystals. The iodine treatment, growth apparatus, procedure and characterization is described. The better crystals when used as room temperature nuclear detectors resolved for the first time the 1.33 MeV photopeak of 60 Co.

Data from a survey of school-age children in Mannheim are used to test the hypothesis that two forms of mental retardation — the ‘pathological’ and the ‘subcultural’ — can be differentiated on the basis of intelligence tests. The findings indicate that this dichotomy is an over-simplification, since frequency of neurological and other organic impairments is inversely related to intelligence level over a fairly wide range. The best cut-off point for screening purposes, in discriminating between severe or moderately severe retardation (usually pathological), on the one hand, and mild retardation (usually subcultural), on the other, corresponds roughly to IQ 50. Use of higher thresholds tends to increase misclassification and to yield less reliable prevalence rates. Classification of children in the IQ-range 50–70 as mentally handicapped (severely or moderately mentally retarded) appears to be subject to social-class bias, and hence could be selectively disadvantageous for children from lower social-status families. can walk, at best, only with some help.

The bulk homogeneity of HgI2 detectors was evaluated by the nuclear spectral response of several detectors fabricated from the same iodine treated crystal grown by TOM (Temperature Oscillating Method) in a horizontal furnace. The 241 Am and 137CS spectral resolution is shown as a function of the detector thickness which ranges from 50 to 1000 ?m and of the bias voltage. The lowest ?T value for holes measured with 55Fe on these detectors is about 10-6 cm2V-l. Nevertheless, the spectral resolution for 137Cs indicates that these detectors must have spots with a higher value of ?Th Uniformity studies by scanning one of the detectors with 241Am are also given and discussed. In addition a 60Co spectrum taken with a 1 mm thick HgI2 detector is shown for the first time.

The crystalline perfection of wire sawn pieces of vapor grown single crystals of mercuric iodide was compared with the perfection of (00l) cleaved sections of the same crystal from which nuclear radiation detectors have been fabricated. The crystalline perfection was studied using neutron and gamma‐ray diffraction rocking curves. Most of the gamma‐ray data were obtained using a high intensity source of 153Sm gamma rays with a wavelength of λ = 0.12 A. Some of the data were obtained using highly penetrating 198Au gamma rays with a shorter wavelength of λ = 0.03 A. The neutrons had a wavelength of λ = 1.07 A. It was found that, in terms of the mosaic spread of the crystals, the cleaved detector plates have a much lower crystalline perfection than the thicker uncleaved detector plates. At the same time, the results show that for detectors cut from the same crystal, the one with the lower spectral resolution for radiation detection will also have a lower perfection and larger width of the gamma‐ray rocking cu...

A detailed semiquantitative electron microprobe analysis has been performed on the segregated impurities of Na2O, Fe2O3, Al2O3, and MgO present in micropockets of natural and synthetic hydrothermally-grown quartz. These oxides most probably combine with SiO2 to form silicates. The Kα1,2 X-rays of Na, Fe, Al, Mg, Si and O have been scanned along the micropockets whose sizes vary between 2 and 30 μm across. Analysis by phase contrast analysis shows that the number varies from about 0.4 × 166/cm2 for Li+ doped; 1.8 × 106/cm2 for Brazilian natural, to about 13.3 × 106/cm2 for Mg2+ doped synthetic quartz crystals. The typical content of two of the impurities in the micropocket can vary between 0.03 to 14.32 wt% Fe and 0.01 to 43 wt% Mg as compared to 0.2 wt% Fe and Mg in the matrix of all crystals as determined by neutron activation. Electron diffraction patterns performed on a thinned section of a crystal revealed some unidentified reflections in addition to the hexagonal quartz reflections and microtwinning around the [110], hinting at a possible crystalline state of the precipitate.

Thin films of Ge produced by the pyrolysis of alkyl germanium tetramethyl germanium and tetraethyl germanium compounds have been studied for their rates of deposition, crystallinity, and carbon contamination. The pyrolysis reaction has been found to be of first order, and the activation energies have been found to vary with concentration of the alkyl germanium compound between the limits of 25–30 kcal/mole for both tetramethyl and tetraethyl germanium. The morphology and crystallinity of the films vary with the chemical and crystalline structure of the substrate. Good quality and uniform films are produced on monocrystalline germanium substrates preetched in situ with gas. The carbon contamination is found to be strongly dependent on the substrate material, and it varies between 25 ppm for germanium and 200–50,000 ppm for tungsten substrates.

The contribution of incomplete charge collection (1− ν ) to the line broadening ΔE col of HgI 2 nuclear detectors has been analysed after subtracting the contribution of the electronic and statistical fluctuation. The measurement of ΔE col versus 1−ν for a given gamma radiation energy corresponds to ΔE col = a (1− ν ) for E γ ranging from 59.6 up to 662 keV where a is a calculated parameter.

X-ray, neutron and gamma ray diffraction rocking curves; X-ray topography; microhardness; and optical microscopic measurements have been performed directly on several mercuric iodide (Hgl2) nuclear radiation detectors fabricated from single crystals grown from the vapor phase. Two types of detectors were measured: spectrometer types (grades A and B), which had resolutions of 5–10% for the 662 keV photopeak of 137Cs, or radiation counters (grades C and D), where the spectral resolution ranged from 11% to no resolution. A good correlation has been found between the detector grade and the full width at half maximum (FWHM) of both the X- and gamma ray rocking curves (i.e., the higher the detector grade (A or B), the narrower the FWHM of the diffraction peak). X-ray topography also correlated with well both the FWHM of the diffraction X-ray rocking curve and the detector grade. The uniformity of the microhardness of the HgI2 detectors was found to be proportional to the nuclear performance of the detector. The better spectrometer-grade detectors were softer and much more uniform in microhardness than the most inferior detectors. The better detectors were also found to have much smoother surfaces than the poorer detectors, as observed by optical microscopy studies.

A method to increase the cyclic oxidation resistance of a chromium and molybdenum rich nickel-based superalloy, Hastelloy-X (48 Ni22Cr18Fe9Mo), is presented, in which the cyclic oxidation resistance is increased at 1100°C. The time after which the total weight change becomes zero is increased from 100 to between 400 and 500 h. The method consists of thermally etching the alloy with gaseous hydrochloric acid (HCL) at 1100°C for approximately 0.5 h. The mechanism of the increased oxidation resistance was investigated using metallography, X-ray diffraction and electron microprobe analysis. As a result of the HTET, a thick and continuous protective subscale of Cr8O3 is formed during the oxidation which acts as an efficient diffusion barrier against further oxidation.

Crystal growth of DyAlO3or Dy3Al5O12by the flux method is in certain cases determined by the size of the crucible starting from the same initial flux mixture to prepare the crystals. A molar mixture composed of 30.5 g PbO, 41.5 g PbF2, 16.5 g Al2O3and 11.5 g Dy2O3produces the garnet phase in a crucible of 40 ml or larger and the perovskite phase in a small crucible of 10 ml.

A composition diagram which compares various mixtures used for growing rare earth garnets is described. The flux components of PbOB2O3 or PbOPbF2 recommended for growth of either rare earth iron, gallium or aluminium garnets are expressed in terms of a pseudoternary diagram. The crystals discussed in this paper are Eu3Fe5O12, Eu3Ga5O12, Tm3Al5O12, Tm3Ga5O12, Yb3Ga5O12, and Yb3Fe2Ga3O12. The crystals are characterized by lattice constant, morphology, and in some cases, by magnetic susceptibility data. In einem Phasendiagramm werden verschiedene Mischungen, aus denen Granate der seltenen Erden gezuchtet werden, miteinander verglichen. Die Komponenten der Schmelzlosungen PbOB2O3 oder PbOPbF2, die zur Zuchtung von Eisen-, Gallium-oder Aluminiumgranaten empfohlen werden, werden in einem pseudoternaren Diagramm dargestellt. Die in dieser Arbeit diskutierten Kristalle Eu3Fe5O12, Eu3Ga5O12, Tm3Al5O12, Tm3Ga5O12, Yb3Ga5O12 und Yb3Fe2Ga3O12 werden durch ihre Gitterkonstante, ihre Morphologie und in einigen Fallen ihre magnetische Suszeptibilitat charakterisiert.

Virtually strain and inclusion free crystals of paratellurite have been grown by Czochralski technique using self prepared TeO2 raw materials. It has been found that both platinum and iridium from the crucible are dissolved by the TeO2 melt causing constitutional supercooling and in certain cases cellular growth. The protective atmosphere of O2 or Ar is also dissolved by the melt contributing to the occurence of gas inclusions. Semi-quantitive analysis of the necessary gradient in the liquid and the rate of growth has been performed in order to prevent constitutional supercooling. For a gradient of 7 °C cm-1, a rate of growth of 0.4 cm/h and a segregation coefficient of Pt in liquid TeO2 of k0 = 0.5, we could estimate the diffusion coefficient of Pt in liquid TeO2 of 0.2×10-5 cm2 sec-1 and a dissolution heat content of 837 J mole-1.

Thin films of TiO2, ZrO2 and HfO2 have been deposited on single crystals of (111) silicon, by chemical vapor deposition (CVD) of the respective organometallic compounds. The thin films of TiO2 have the anatase structure while ZrO2 and HfO2 are monoclinic. All films are easily etched by 5% HF solution, while films of TiO2 are also etched by 70% H2SO4. The indices of refraction of the thin films are 2.05–2.26 for TiO2, 1.94 for ZrO2 and 2.02 for HfO2. All the oxide films show good MOS C-V characteristics, the flatband voltages having values near zero. The bias-temperature (B-T) tests on C-V curves in the case of HfO2 show high stability.

The preparation and heat-treatment of single crystals of spinel lithium ferrite, LiFe 5 O 8 , are described. X-ray study confirms the existence of two phases, one ordered (α) and one disordered (β), and interplanar spacings are given for these. Two new high-temperature phases, named γ and δ, have been discovered. These appear to be associated loss of lithium from the material when it is heated above 1000°C in a vacuum of 10 −3 mm Hg. Once in the γ form, the material cannot be returned to the α or β forms, but the γ → δ transformation, occuring at 1250°C, is reversible.