TiC Single Crystals Research Articles

TiB2 and TiC single crystals by plasma-arc remelting of SHS products

The growth of TiB2 and TiC single crystals by plasma-arc remelting of SHS products was explored. The process was markedly improved by using special stabilization systems. The synthesized crystals exhibited a cellular structure and a strong dependence of the longitudinal distribution of impurity elements on a growth rate.

FZ 法による TiC 単結晶の育成

FZ 法による TiC 単結晶の育成

Overview of the TiC/TiO 2 (rutile) interface

The structural and chemical characterization of the TiC/rutile interface that grows in the high-temperature and low-oxygen partial pressure oxidation of TiC single crystals is reported. Based on previous data of micro-Raman and Auger electron spectroscopy (AES)–scanning electron microscopy (SEM) profiles of the TiC/rutile interface cross-section, a Ti oxycarbide phase is expected to form at the TiC/rutile interface. In order to be consistent with the above mentioned data, Ti oxycarbide should form by partial substitution of C with O without producing any change in the rock-salt structure of TiC except to small changes in the lattice parameter. Following the Ti oxycarbide e-gun synthesis by X-ray diffraction (XRD) analysis, the enhancement of the O substitution in the C sublattice of TiC has been shown. The final product has been identified by chemical analysis as Ti 1.00±0.01C 0.49±0.01O 0.4±0.1 having a XRD spectrum almost identical to TiC with a relative change of the lattice parameter equal to −0.8%. This result confirms the reason why no other signals other than the signals of amorphous carbon and rutile appear in the micro-Raman profiles of the TiC/TiO 2 interface as well as the reliability of the oxidation mechanism elsewhere proposed.

TEM observation of oxide scale formed on TiC single crystals with different faces

Cross-sectional observation of the oxide scale formed by oxidation of TiC single crystals with (100), (110) and (111) faces at 1500 °C for 30 min in a mixed gas of Ar/O 2 ( P O2=0.08 kPa) was performed by transmission electron microscope (TEM). The oxide scale was composed of outer (zone 2) and inner (zone 1) subscales. TEM and selected area electron diffraction combined with X-ray energy dispersion analysis showed that the zone 2 consists of rutile and pores and the zone 1 of carbon and titanium oxide, identified as Ti 3O 5 in the oxide scale formed on the (110) face. Zone 1 formed on the (100) and (111) faces showed crisscross patterns, in contrast to the (110) with the wavy lamellar pattern.

Rutile Growth Mechanism on TiC Monocrystals by Oxidation

The surfaces (111) and (110) of TiC single crystals have been exposed to an Ar/O2 mixture at low oxygen content (≈270 ppm, Ptot = 2 bar abs.) and 1073 K. The oxygen consumption and interaction gaseous products have been detected, respectively, through zirconia stabilized oxygen sensors and a quadrupole mass spectrometer. The cross-sections of oxidized samples have been analyzed by micro-Raman and SEM techniques. Concentration profiles of amorphous carbon and rutile have been detected along the carbide oxidized layer interface. This confirms previous observations of retention of carbon during the oxidation of the transition metal carbides. The results obtained have been compared with our previous experiments which showed the following structural relationships: TiO2(200)||TiC(111) and TiO2(110)||TiC(110). The rutile (200) growth rate was found to be higher than the growth rate of rutile (110). Oxidation routes have been proposed.

Structural characterization of TiO 2 films obtained by high temperature oxidation of TiC single crystals

The possibility of obtaining an oriented TiC-TiO 2 junction was investigated. The (110) and (111) crystallographic planes of TiC were exposed to an Ar/O 2 stream with an oxygen content of 180 ppm at 815 °C. Through the oxygen consumption measurement, the oxidation kinetics were monitored both in non-isothermal and isothermal conditions. The parabolic rate constants for the rutile growth on both the orientations of the TiC substrates were calculated. From their values, some information on the diffusion coefficient of the oxygen vacancies related to the oriented growth of rutile was also obtained. A detailed structural investigation was performed on TiO 2 (rutile) grown on single crystal TiC substrates with different orientation. Environmental Scanning Electron Microscopy (ESEM), X-ray Diffraction (XRD) and X-ray Diffraction texture analysis techniques were utilized to obtain morphological and crystallographic information on the TiO 2 films. Analysis of XRD spectra and XRD texture measurements show that growth of the TiO 2 layers is strongly influenced by the crystallographic orientation of the substrate. A correlation between the crystal structure of TiO 2 layers and the single crystal orientation of the TiC substrate is discussed in the paper.

Weak Interaction of Oxygen with Some Refractory Carbides

The reactivity of NbC (single crystal and polycrystalline), TiC (single crystal and polycrystalline), and polycrystalline ZrC in the temperature range from ambient to 1020°C and at oxygen partial pressures from 0.07 to 9 Pa is reported. The reactivities of the principal (hkl) planes of TiC as well as the polycrystal are also measured at 0.8 Pa of The reactivity ratio order is 1.0, 1.2, and 1.9, respectively, for (111), (100), and (110) planes. Under these conditions, laths at right angle of epitaxial rutile were observed. The comparison of the reactivity between NbC(100) and polycrystalline NbC has been determined and some tentative data are given on the reactivities of the other planes. The reactivity at higher oxygen partial pressures was also measured for TiC(111) and in these conditions a well-defined TiC-rutile ceramic to ceramic joint has been obtained. The reactivity and in situ electrical resistivity measurements on polycrystalline TiC and ZrC, both as received and high temperature, high vacuum treated, are presented. Large differences in the reactivity hystereses were found. The same result was not found in the behavior of the resistivity. © 2001 The Electrochemical Society. All rights reserved.

Oxidation of Hafnium Carbide and Titanium Carbide Single Crystals with the Formation of Carbon at High Temperatures and Low Oxygen Pressures

The isothermal oxidation of the 200 face of HfC and TiC single crystals was performed at temperatures of 700°—1500°C and at oxygen pressures of 0.08—80 kPa for 4 h. The weight gain by oxidation of the two crystals was followed using an electromicrobalance. A polished cross section of the oxidized crystals was observed using backscattered electron imaging in a scanning electron microscope. Quantitative chemical analysis for Hf, Ti, O, and C was performed by wavelength‐dispersive X‐ray microanalysis. The early‐stage oxidation kinetics of HfC crystals were described by the contracting volume equation, followed by slowed reaction in the latter stage, whereas the same equation was applied to the oxidation of TiC over the entire oxidation time. The preferred {200} orientation of monoclinic HfO2 occurred on the oxidized surface of the HfC crystal. The oxide scale on the HfC crystal consisted of a compact and pore‐free black inner scale (zone 1) and a white/gray outer scale that contained many pores (zone 2). Zone 1 contained ∼25 at.% unoxidized carbon, and zone 2 contained 6—11 at.% carbon. The oxide scale of TiC was composed of an inner dense lamella subscale (zone 1) with a carbon content of 7—23 at.% and an outer region with laminations that was separated by pores and cracks (zone 2). The Ti3O5 phase, which exhibits a strong 020 line, was formed at depths of ≥40 μm in the scale obtained at 1500°C. Treatment with a concentrated HF solution allowed zone 1 to be separated from the HfC crystal in the form of carbon‐containing films, which were characterized using Raman spectroscopy and transmission electron microscopy.

Inelastic x-ray scattering from TiC and Ti single crystals.

Inelastic x-ray scattering spectra were measured with incident x rays having an energy near 8 keV for a range of momentum transfers q extending from 0.70 to 2.0 \AA{} $^{\mathrm{\ensuremath{-}}1}$. We find spectral features corresponding to valence electron excitations, as well as Raman scattering corresponding to excitation from the 3p core states to the 3d valence states of Ti. The spectral features corresponding to valence electron excitations lie in the regime conventionally interpreted as a bulk plasmon together with intraband and interband transitions. We compare our data for TiC at q=1.05 \AA{} $^{\mathrm{\ensuremath{-}}1}$ with calculations for the dynamical dielectric constant \ensuremath{\varepsilon}(q,\ensuremath{\omega}) based on local-density theory. The agreement between the data and calculations permits us to interpret certain features in the spectra as arising from band transitions out of the strongly hybridized C 2p--Ti 3d band. The energy loss position of the Raman scattering peak is independent of momentum transfer for both TiC and Ti and lies at 48 eV for Ti. This value is above the highest-lying x-ray ultraviolet absorption resonance for atomic Ti at 43.5 eV. This shift in the data to higher energy transfer is consistent with electron energy loss spectra and photoemission results reported in the literature and indicates that important physical processes are not encompassed within existing theoretical approaches to x-ray Raman scattering. \textcopyright{} 1996 The American Physical Society.

Ion channeling studies of C + irradiated TiC single crystals

TiC 0.83 crystals have been irradiated in a random direction at room temperature to 5 × 10 15/cm 2 with 350 keV C + ions. Depth profiles of displaced atoms from the carbon and titanium sublattices have been extracted from 1.25 MeV D + backscattering energy spectra and proton energy spectra produced by the 12C(d,p) 13C nuclear reaction, respectively, by comparison of the undamaged and damaged areas oriented along the 〈110〉 direction. The experimental data have been analyzed using a dechanneling theory for diatomic lattices developed in the present study. The profiles obtained for the displaced Ti- and C-atoms are compared with the simulated profiles obtained using a Monte Carlo practice transport code. The results suggests that the threshold displacement energy is different for Ti- and C-sublattices: the displacement energy for the C-sublattices is smaller than that of the Ti-sublattices in TiCo 0.83 crystals.

Flux growth and characterization of TiC crystals

Single crystals of TiC were grown using nickel and cobalt metal as a flux at soaking temperatures of 1500 to 1800° C and at compositions of 12.5 to 30 mol% TiC. The use of cobalt flux produced crystal sizes less than 0.5 mm under all conditions. With a nickel flux, a maximum crystal size of 1.5 mm was obtained at 1700 and 1800°C and at 20 and 25 mol% TiC composition, using a cooling rate of 3° C min−1. A slower cooling rate of 0.2° C min−1 also gave crystals of 1.5 mm at 1600° C. The crystals were cubic and metallic-lustre silver grey in colour. The lattice parameter of the crystal was measured to bea 0 = 0.432 75 ± 0.000 05 nm, with nearly stoichiometric composition. The grown faces were of the {1 0 0} family with a dislocation density around 107 cm-2. The Vickers' microhardness on these faces was in the range 2600 to 2800 kg mm−2. The nickel impurity and free carbon contents in the crystals were 700 to 1000 p.p.m. and 0.8 to 4 wt%, respectively.

Growth conditions of high purity TiC single crystal using the floating zone method

Abstract In the preparation of TiC single crystal with high purity from a self-combustion rod by a floating zone technique, the dependence of the crystal quality on the growth conditions was examined. The quality of the prepared crystals was determined by measuring the etch pit density and X-ray diffraction of the grown crystals. The quality of the crystals was partially improved by increasing the growth rate and decreasing the crystal diameter.

Preparation of TiC single crystal from self-combustion rod by floating zone method

In order to prepare a single crystal of TiC with a high purity using the floating zone method, the feed rods were prepared by the self-combustion reaction of Ti metal and carbon. The control of the composition of the feed rod, the impurity refining, the density of the feed rod and the degree of the reaction were examined in the process of self-combustion. Using the feed rod prepared in this way, a high purity single crystal with controlled composition was prepared by a modified zone leveling method.

State‐Variable Analysis of Inelastic Deformation of TiC Single Crystals

The log σ‐log ɛ data obtained from load relaxation experiments on TiC single crystals, at 900° to 1400°C, were analyzed in terms of Hart's two‐branch rheological model. The analysis verified the existence of a mechanical equation of state within the ranges of stress, strain rate, and temperature employed. Straight and clustered dislocations dominated the micro‐structure of samples at low temperatures, while well‐developed cell structures dominated the microstructure of samples at high temperatures. The observed changes in log σ‐log ɛ curves and the dislocation structure both indicate that, in addition to the glide‐controlled mechanisms, climb/cross‐slip‐controlled mechanisms contribute significantly to the plastic flow with increasing temperature.

Electrical resistivities in single crystals of TiC x and VC x

TiCx and VCx have wide non-stoichiometric composition ranges which come only from the carbon vacancies. High purity single crystals with controlled compositions were prepared, and their electrical resistivities at 4.2 and 298 K were measured as a function of composition. In the case of TiCx whose carbon vacancies are disordered in the lattice, the dependence of the residual resistivity on the composition was interpreted' by applying Nordheim's rule to the vacancy scattering and by considering the change in carrier density due to the introduction of vacancies. In addition, the difference in the resistivity between 4.2 and 298 K was discussed. In the case of VCx whose carbon vacancies are ordered, the dependence of the resistivity on the composition ranges of the ordered phases was examined in detail.

表面処理ＴｉＣ〈１１０〉フィールドエミッターの特性

It has been found that a new field emitter using a -oriented TiC single crystal (TiC ) tip shows highly stable emission under appropriate “surface-processing”. The field emission pattern and current stability of the surfaceprocessed TiC tip are discussed compared with those of the clean TiC tip.

Surface compositional changes of TiC, B 4C and SiC at high temperatures

Changes in the surface composition of TiC, B 4C and SiC single-crystals and coatings have been studied by using Auger electron spectroscopy. The analysis of the surface composition was performed under a heat treatment up to 1500°C and/or an argon-ion bombardment (3 keV. 7 μA/cm 2). In both the TiC single-crystal and coating, an increase in the surface composition of carbon atoms was observed as the temperature was raised, regardless of the bombardment. Carbon atoms diffused to the surface of the coating to form graphite-type carbon above 1000°C. In case of the B 4C single-crystal, a remarkable increase in surface concentration of carbon atoms was observed at 1000°C and 1250°C, while such a drastic change was not observed during the bombardment. On B 4C coating, graphite-type carbon atoms existed in the near-surface region at 1500°C. On the SiC single-crystal, the surface composition of carbon atoms increased on raising the temperature regardless of the bombardment. At 1500°C the surface was completely covered with graphite-type carbon atoms.

Field electron emission properties of TiC single crystals

Very stable field electron emission from TiC single crystals was observed. No current fluctuations were included in an emission current of 10 μA in a vacuum of 10−8 Pa. Step- and spike-like current fluctuations were slightly included when the emission current was large. The frequency and the amplitude of the current fluctuations were largely dependent on the sorts of the residual gas molecules. For instance, when the total emission current was 10 μA, no current fluctuation was included in 10−6 Pa of H2; on the other hand, fluctuations of several percents were included in 10−7 Pa of O2.

Surface composition change of TiC and SiC under hydrogen ion bombardment

Surface composition changes of TiC and SiC single crystals under hydrogen ion bombardment have been investigated. The depletion of carbon atoms in the surface region was observed in both compounds. The depletion was enhanced as the primary ion energy decreased, though in SiC the energy dependence was less prominent. In TiC the dependence of depletion on the ion energy can be explained by the change of the sputtering mechanisms with the ion energy. In addition chemical effects seem to contribute to the depletion, which become prominent in the lowest energy region. In SiC a region enriched with carbon atoms was observed beneath the surface, probably resulting from recoil implantation of carbon atoms.

ＴｉＣ単結晶の電界放射電子のフラッシング温度依存性

Field electron emission from TiC single crystals of and directions was examined. Very stable electron emission was observed when the crystals were flashed at a certain temperature. The current fluctuations due to the residual gas were also reduced. The flashing temperatures make changes in the emission patterns, which render the shapes of the top of the field emission tip. It is concluded that the surface near the top is constracted by (100) and (111) facets independently of the crystal orientations, and this conclusion is confirmed by the Fowler-Nordheim plot of the emission current.