Effect Of Isothermal Annealing Research Articles

Effect of isothermal annealing on CdTe and the study of electrical properties of Au–CdTe Schottky barriers

Single-crystal CdTe was grown using the vapour phase technique. The dice were suitably etched and isothermally annealed in air for different times (0.5, 1, 2, 3, and 4 h) at 673 K. Schottky diodes were fabricated by vacuum evaporation of Au onto CdTe single-crystal substrates which were isothermally annealed. The behaviour of Au–CdTe devices was studied as a function of time using capacitance–voltage and current–voltage analysis. The isothermal anneal technique was found to produce a significant change in the electrical properties of Au–CdTe Schottky barriers such as barrier height, carrier concentration, ideality factor and depletion width. The results were discussed in terms of various theories of Schottky barrier formation.

Effects of isothermal annealing on the microstructure and mechanical properties of SiC ceramics hot-pressed with Y2O3 and Al2O3 additions

Abstract Silicon carbide compacts containing various α contents and 7 wt.% of Y2O3 and Al2O3 (weight ratio 60:40) were hot-pressed and isothermally annealed at 1950 °C to study the coarsening behavior of SiC grains and the crystallization of the grain-boundary glass phase. The samples which were prepared from the powder compacts containing small amounts of the α phase contained well-developed large plate-like grains in fine matrix grains and showed enhanced fracture toughness. A subsequent isothermal annealing was effective in controlling the grain boundary phase and resulted in the enhancement of mechanical properties. When the crystallization of the grain boundary phase leads to an aluminum-rich phase (Y–Al garnet) during the intermediate stage of annealing, flexural strength is improved. On the other hand, the fracture toughness can be increased when crystallization of the grain boundary glass is directed to an yttrium-rich phase during extended annealing. These results were explained in terms of the thermal mismatch between the SiC grain and the remaining glassy phase.

Effect of annealing in the nematic phase on the transient shear response of thermotropic liquid-crystalline polymers

The effect of isothermal annealing, prior to start-up of shearing flow, in the nematic region on transient shear responses was investigated using a glassy thermotropic liquid-crystalline polymers (TLCP), PSHQ9, and a crystalline TLCP, PSHQ10. It was observed that the peak value of first normal stress difference (N1,peak+) of PSHQ9 remains constant, independent of the duration of annealing prior to start-up of shearing flow, whereas the N1,peak+ of PSHQ10 increases steadily with increasing period of annealing in the nematic phase prior to start-up of shearing flow. On the other hand, it was observed that the peak value of shear stress (σpeak+) remains constant in both PSHQ9 and PSHQ10, independent of the duration of annealing in the nematic phase prior to start-up of shearing flow. The observed dependence of N1,peak+ for PSHQ10 on the duration of isothermal annealing in the nematic phase is found, via differential scanning calorimetry, to be attributable to the perfection (or growth) of the crystals in PSHQ10 during annealing prior to start-up of shearing flow. The experimental observations made from this study suggest that glassy TLCPs be used to obtain reproducible transient shear responses.

Effects of Metastable Phase Formation on the Magnetic Properties of Pr<SUB>4.5</SUB>Fe<SUB>77</SUB>B<SUB>18.5</SUB> Amorphous Ribbons

The effects of isothermal annealing on the magnetic properties of Pr4.5Fe77B18.5 amorphous ribbons have been investigated. Two separate reactions increasing coercive force ( Hc) were recognized during the progress of annealing. In the first reaction, hard magnetic Pr 2Fe14B particles with nanoscale diameters precipitated in the vicinity of Fe 3B and Pr2Fe23B3 particles. The precipitation of fine Pr 2Fe14B particles increased Hc largely but reduced saturation magnetization ( Ms) significantly. In the second reaction, the Pr 2Fe23B3 particles decomposed into Pr2Fe14B particles containing very fine α-Fe particles within them. This resulted in the second increase in Hc due to both the volume fraction increase of Pr2Fe14B particles and the exchange-coupling interaction between the Pr2Fe14B grains and α-Fe particles within them. This phenomenon was observed originally in the present study. In the final stages of annealing, both Hc and Ms were decreased substantially by the decomposition of Pr2Fe14B into PrFe4B4 particle in addition to the coarsening of α-Fe particles.

Diffusion of Nitrogen Atoms Implanted into Synthetic Diamonds

The effect of isothermal annealing on the depth profiles of nitrogen atoms implanted into synthetic diamonds is studied by secondary-ion mass spectrometry. The annealing is performed under vacuum at 1400°C for 1, 5, or 20 h. It is found that the depth profile broadens on a macroscopic scale with annealing time. The broadening is successfully represented by a mathematical model of diffusion. The diffusion coefficient is roughly estimated at 2.3 × 10–15, 8.5 × 10–16, and 3.7 × 10–16 cm2/s for annealing times of 1, 5, and 20 h, respectively.

Destruction of monocrystals of potassium dihydrophosphate in the process of heating

We study the effect of isothermal annealing of KH2PO4 monocrystals in the temperature range 180–210°C on the quality of their structure and phase composition by the method of X-ray diffraction analysis and microscopically. It is shown that in the process of heating followed by cooling, the specimens undergo both the phase transition from the tetragonal to monoclinic modification and the inverse transition, namely,\(\bar 4\)2m → P21 →\(\bar 4\)2m, and these transitions are accompanied by the structural transition from monocrystals to polycrystals. This leads to the formation of a branched system of microcracks and, as a result, to the turbidity and degradation of the material. The indicated processes are explained by the great difference between the lattices of the tetragonal and monoclinic phases and stresses formed in the course of these phase transformations.

Effect of isothermal annealing on the properties of rolled products of powder alloys of the system Fe-Cr-Ni

Effect of isothermal annealing on the properties of rolled products of powder alloys of the system Fe-Cr-Ni

Effect of Isothermal Annealing on Crystallization Mechanism of Amorphous Ni65Cr16P19 Metallic Alloys

Crystallization behavior of amorphous Ni65Cr16P19 metallic alloy during the isothermal annealing process from 617 K to 648 K was studied using differential scanning thermal analysis and X-ray diffraction analysis. Two crystallization peaks are observed. The activation energies E A for the crystallization are determined to be 403 kJ/mol and 306 kJ/mol for the first and the second peak, respectively. Ni crystals precipitate in the first peak by a two-dimensional crystallization mechanism with a constant nucleation rate, and stable Ni3P crystallizes in the second peak. With the use of the Avrami index, the activation energy for nucleation of the Ni crystal is determined to be 470 kJ/mol.

Effect of isothermal annealing on the magnetic behavior of amorphous ferromagnets with composition near the percolation threshold. I. Outside the critical region

Results of detailed ferromagnetic resonance measurements taken on amorphous (a-) Fe90+XZr10−X alloys with X=0 and 1 in the horizontal-parallel and vertical-parallel sample configurations at a fixed microwave frequency of ≂9.23 GHz in the temperature range 77 to 300 K before and after these alloys have undergone isothermal annealing treatment at 400 K for durations of time, tA, ranging from 10 to 240 min are presented and discussed. While only a single (primary) resonance is observed for T≲TC (the Curie temperature), an additional (secondary) resonance first appears at T≂TC and then gets fully resolved for T≳(TC+10 K). For the primary resonance (i) the ‘‘in-plane’’ uniaxial anisotropy field, Hk, and the Gilbert damping parameter, λ, both scale with the saturation magnetization, MS, in the temperature ranges 77 K≤T≲TC and 0.5TC≲T≲0.8TC, respectively, at all tA including tA=0; (ii) isothermal annealing has essentially no effect on MS(T), the ‘‘peak-to-peak’’ linewidth, ΔHpp(T), ΔH0 (the frequency- and temperature-independent contribution to ΔHpp) and λ(T); (iii) with increasing Fe concentration, the value corresponding to the peak in λ(T) decreases, λ(0.5TC) increases while λ(300 K) stays constant at 1×108 s−1, and (iv) isothermal annealing up to a time duration of 30 min results in an enhancement of about 1.5% in TC and a reduction of nearly 40% in the characteristic temperature T0 (which is a measure of the re-entrant transition temperature) whereas no further change occurs in both TC and T0 at higher annealing times. By contrast, for the secondary resonance, (a) Hk≂0 at all temperatures T≳TC and values of tA covered in the present experiments, (b) isothermal annealing leaves the resonance field unaltered, and (c) a steep decline in the value of ΔHpp′ occurs for tA≤10 min but at higher values of tA, ΔHpp′ remains constant for a-Fe90Zr10 whereas it increases at first and then saturates in the case of a-Fe91Zr9. The effect of isothermal annealing on the quantities of interest, i.e., TC, T0, ΔHpp, etc., can be qualitatively understood in terms of a finite spin clusters plus an infinite ferromagnetic matrix model.

Effect of isothermal annealing on the magnetic behavior of amorphous ferromagnets with composition near the percolation threshold. II. In the critical region

Extensive ferromagnetic resonance (bulk magnetization) measurements have been performed on amorphous Fe90+XZr10−X alloys with X=0 and 1 (X=0, 1, and 2) in the critical region, −0.1≲(T−TC)/TC≲0.1, before and after they had been subjected to isothermal annealing treatment at 400 K for durations of time, tA, ranging from 10 to 240 min (in the ‘‘as-quenched’’ condition) with a view to study the alterations in the critical behavior as the tricritical point, Xc≂3, is approached along the ferromagnetic (FM)-paramagnetic (PM) transition line in the magnetic phase diagram and as the topological (TSRO) as well as chemical (CSRO) short-range order undergo changes on account of structural relaxation. Asymptotic values of the critical exponents β and γ and critical amplitudes m0 and (m0/h0) for spontaneous magnetization and initial susceptibility have been determined for the as-quenched as well as annealed samples. Consistent with the predictions of the infinite FM matrix plus finite spin clusters model and with the well-known Harris criterion, change in CSRO and TSRO caused by altering the alloy composition and/or by isothermal annealing leaves the values of the critical exponents β and γ, and the universal ratio m0/MS(0) unaltered from those predicted by the renormalization group theory for an ordered spin system with spatial as well as spin dimensionality of three. The presently determined values of the critical amplitudes reveal that the fraction of spins that actually participates in the FM-PM transition is as low as ≊10% and reduces drastically as X→Xc but for a given composition, it declines slowly with increasing tA.

Effect of isothermal annealing on the Bordoni relaxation in cold worked copper

The Bordoni relaxation in ultra-purity cold worked copper subsequent to isothermal annealing in the temperature range 298–423 K at 700 Hz frequency is investigated using a set up based on the electrostatic system. The Bordoni peak is observed at 79±2 K. The annealing characteristics of the Bordoni peak are found to be of complex nature. The decay and subsequent regrowth of the peak following annealing above room temperature are interpreted in terms of defects diffusing to dislocations and their removal from dislocations, respectively. The calculated activation energy values for the first decrease (0.55 eV), first increase (0.24 eV) and first minimum (0.27 eV) are in good agreement with the activation energies for interstitial and divacancy diffusion estimated by different workers. The activation energy for divacancy diffusion is computed to be 0.49 eV.

Effect of isothermal annealing of amorphous alloys on their tendency toward pitting corrosion

. Seek, "Breakthroughs in rapid solidification," Am. Machinist, 125, No. 3, 69-71 (1981). "Trends in powder metallurgy technology," Met. Prog., 121, No. i, 38-49 (1982). J. Niewiarowski and H. Matyja, "Splat quenching of high-speed tool steels," in: 3rd internat/ Conf. Rapidly Quenched Metals, The Metals Soc., Vol. i, London (1978), pp. 193196. A. Inoue, T. Masumoto, S. Arakawa, and T. Iwadachi, "Mechanical properties and thermal stability of new type amorphous high-carbon alloy steels," in: 3rd Internat. Conf. Rapidly Quenched Metals, The Metals Soc., Vol. i, London (1978), pp. 265-272. J. V. Wood, J. K. Bigham, and J. V. Bee, "Rapid solidification of high alloy steels and nickel superalloys," in: 3rd Internat. Conf. Rapidly Quenched Metals, The Metals Soc., Vol. i, London (1978), pp. 94-101. J. J. Rayment and B. Cantor, "Splat-quenched tungsten steels," in: 3rd Internat. Conf. Rapidly Quenched Metals, The Metals Soc., Vol. i, London (1978), pp. 85-93.

Coarsening of γ′-precipitates in single-crystal superalloy SRR 99

The effects of isothermal annealing between 800 and 1200°C on the microstructure of single–crystal SRR 99 have been investigated. During aging at either 800 or 900°C, the precipitates adopt an irregular, rounded, and highly interconnected array which suggests that they have undergone coalescence. Aging at higher temperatures was found to produce a regular cuboidal precipitate morphology, although long–term aging promoted the formation of γ′-‘rafts’. The precipitate size distributions were found to be broader than those predicted by the Lifshitz-Slyosov and Wagner theory, and the coarsening kinetics also showed significant deviations from the power law prediction of this theory. The reasons for these deviations are discussed in the light of the available models, and it is suggested that a progressive transition in the dominant coarsening mechanism takes place.MST/371

Coarsening of γ′-precipitates in single-crystal superalloy SRR 99

AbstractThe effects of isothermal annealing between 800 and 1200°C on the microstructure of single–crystal SRR 99 have been investigated. During aging at either 800 or 900°C, the precipitates adopt an irregular, rounded, and highly interconnected array which suggests that they have undergone coalescence. Aging at higher temperatures was found to produce a regular cuboidal precipitate morphology, although long–term aging promoted the formation of γ′-‘rafts’. The precipitate size distributions were found to be broader than those predicted by the Lifshitz-Slyosov and Wagner theory, and the coarsening kinetics also showed significant deviations from the power law prediction of this theory. The reasons for these deviations are discussed in the light of the available models, and it is suggested that a progressive transition in the dominant coarsening mechanism takes place.MST/371

A SAXS study of the crystallization behavior of the Pd 72B 28 glassy alloy

The effects of isothermal annealing of a Pd 72B 28 amorphous alloy were followed up to complete crystallization by small angle X-ray scattering and differential scanning calorimetry. An amorphous-in-amorphous phase separation develops at the beginning of the transformation process. A eutectic mechanism for a demixing stage was inferred from the SAXS integrated intensity behavior. The two separated phases undergo a second metastable-to-stable transformation toward the Pd 5B 2 compound suggested by the equilibrium diagram.

Stress relief of basal orientation zinc oxide thin films by isothermal annealing

The effect of isothermal annealing on residual strain in the lattice of as-deposited basal crystallographic orientation zinc oxide was studied. Films were prepared by rf diode sputter deposition from a zinc oxide target and annealed in air for 5 to 1995 min at 300 or 500 °C. The change in crystallography as a result of annealing was determined by x-ray diffraction. The results show that as-deposited films have a residual tensile strain along the c axis with an average value of +0.62%. Strain relaxation begins to occur after 5 min at 300 °C. The small activation energy, ∼0.2 eV, suggests that interstitial diffusion assisted by local plastic strain may be the process by which strain relaxation initiates. Annealing at 500 °C for longer than 5 min causes a compressive strain to develop along the c axis upon cooling. This effect is attributed to the difference in the coefficient of thermal expansion of zinc oxide and silicon. Comparison with other annealing studies suggest that the magnitude of this effect is likely to be dependent upon the structure of the film–substrate interface.

PIEZOELECTRICITY AND ENTHALPY RELAXATION IN THE COPOLYMER OF VINYLIDENE CYANIDE AND VINYL ACETATE

In amorphous copolymer of vinylidene cyanide and vinyl acetate showing high piezoelectricity, a considerable enthalpy relaxation was observed at the glass transition temperature (Tg) by annealing below Tg. The relationships between the excess thermodynamic properties and the piezoelectric properties were elucidated by investigating the effect of isothermal annealing on the depolarization process by the thermal stimulated current (TSC) measurements. From the comparison of activation energies between the enthalpy relaxation and the depolarizing process, the molecular motion associated with the energy absorption in DSC endothermic peak is considered to be the conformational rearrangement of C-CN bond induced by dipole rotations in the glassy matrix. Also corresponding changes in molecular mobility have an influence upon the stability of dipole orientation in depolarizing process. Consequently, annealing below Tg increases the stability of the remanent polarization (Pr) and its corresponding piezoelectricity.

Raman scattering studies on slow crystallization process from amorphous PbTiO3

Abstract The effect of isothermal annealing of amorphous PbTiO3 below the crystallization temperature, Tcrys, has been investigated by Raman scattering measurements. The occurrence of the crystallization has been confirmed by the appearance of the soft mode. In the crystallized sample, the possibility of the occurrence of a crystalline phase, which is different from the tetragonal PbTiO3 of perovskite structure, has been pointed out.

Slow crystallization process from amorphous PbTiO3

Abstract The effect of isothermal annealing of amorphous PbTiO 3 at a temperature below the crystallization temperature, T crys, has been investigated. Time dependent dielectric constant in the annealing process has been observed. From the experimental results, both the existence of the glass transition temperature, T g, and the steadiness of dielectric constant at room temperature have been established

Hopping conduction in Cr-doped amorphous gallium arsenide films

Amorphous Cr-doped GaAs has been prepared by rf sputtering and the dc conductivity measured at fields up to 10 7 V/m and temperatures down to 80 K. The results are explained in terms of field-assisted hopping. Effects of isothermal annealing at temperatures up to 200°C are studied. The studies are repeated and the results compared with undoped a-GaAs. Room temperature resistivities of a-GaAs: Cr, a-GaAs and polycrystalline GaAs are also compared. The recrystallization temperature for a-GaAs films is determined to be between 320°C and 340°C.