21 research outputs found
Calculation of the P-T phase diagram and tendency toward decomposition in equiatomic TiZr alloy
Electronic, structural and thermodynamic properties of the equiatomic alloy
TiZr are calculated within the electron density functional theory and the
Debye-Gruneisen model. The calculated values of the lattice parameters a and
c/a agree well with the experimental data for the alpha, omega and beta phases.
The omega phase is shown to be stable at atmospheric pressure and low
temperatures; it remains energetically preferable up to T=600K. The alpha phase
of the TiZr alloy becomes stable in the range 600K<T<900K, and the beta phase
at temperatures above 900K. The constructed phase diagram qualitatively agrees
with the experimental data available. The tendency toward decomposition in the
equiatomic alloy omega-TiZr is studied. It is shown that in the ground state
the omega phase of the ordered equiatomic alloy TiZr has a tendency toward
ordering, rather than decomposition.Comment: 6 pages, 8 figure
Application of Thin Piezoelectric Films in Diamond-Based Acoustoelectronic Devices
The theory of external loading influence on acoustic parameters of piezoelectric five-layered structure as “Al/(001) AlN/Mo/(001) diamond/Me” has been developed. Oscillations in diamond-based high-overtone bulk acoustic resonators (HBARs) have been investigated in terms of 3D FEM simulation. Peculiarities of technology of aluminum-scandium nitride (ASN) films have been discussed. Composition Al0.8Sc0.2N was obtained to create the diamond-based HBAR and SAW resonator. Application of ASN films has resulted in a drastic increasing an electromechanical coupling up to 2.5 times in comparison with aluminum nitride. Development of ASN technology in a way of producing a number of compositions with the better piezoelectric properties has a clear prospective. SAW resonator based on “Al IDT/(001) AlN/(001) diamond” structure has been investigated in the band 400–1500 MHz. The highest-quality factor Q ≈ 1050 was observed for the Sezawa mode at 1412 MHz. Method of measuring HBAR’s parameters within 4–400 K at 0.5–5 GHz has been developed. Results on temperature dependence of diamond’s Q-factor at relatively low frequencies were quite different in comparison with the ones at the frequencies up to 5 GHz. Difference could be explained in terms of changing mechanism of acoustic attenuation from Akhiezer’s type to the Landau-Rumer’s one at higher frequencies in diamond
Strain-induced phase transformations under compression, unloading, and reloading in a diamond anvil cell
Strain-induced phase transformations (PTs) in a sample under compression, unloading, and reloading in a diamond anvil cell are investigated in detail, by applying finite element method. In contrast to previous studies, the kinetic equation includes the pressure range in which both direct and reverse PTs occur simultaneously. Results are compared to the case when “no transformation” region in the pressure range exists instead, for various values of the kinetic parameters and ratios of the yield strengths of low and high pressure phases. Under unloading (which has never been studied before), surprising plastic flow and reverse PT are found, which were neglected in experiments and change interpretation of experimental results. They are caused both by heterogeneous stress redistribution and transformation-induced plasticity. After reloading, the reverse PT continues followed by intense direct PT. However, PT is less pronounced than after initial compression and geometry of transformed zone changes. In particular, a localized transformed band of a weaker high pressure phase does not reappear in comparison with the initial compression. A number of experimental phenomena are reproduced and interpreted
Raman spectroscopy on carbon nanotubes at high pressure
Raman spectroscopy has been the most extensively employed method to study
carbon nanotubes at high pressures. This review covers reversible
pressure-induced changes of the lattice dynamics and structure of single- and
multi-wall carbon nanotubes as well as irreversible transformations induced by
high pressures. The interplay of covalent and van-der-Waals bonding in
single-wall nanotube bundles and a structural distortion near 2 GPa are
discussed in detail. Attempts of transforming carbon nanotubes into diamond and
other "superhard" phases are reviewed critically.Comment: 33 pages, 20 figures, review article, to appear in J. Raman
Spectroscop
Surface tension of copper-nickel alloy, silicon and graphite at normal and high pressure
Translated from Russian (Fiz. Khim. Obrab. Mater. 1997 (3) p. 105-108)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.190(9586)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Raman Spectra and Bulk Modulus of Nanodiamond in a Size Interval of 2–5 nm
Abstract Nanodiamond in a 2–5-nm size interval (which is typical for an appearance of quantum confinement effect) show Raman spectra composed of 3 bands at 1325, 1600, and 1500 cm−1 (at the 458-nm laser excitation) which shifts to 1630 cm−1 at the 257-nm laser excitation. Contrary to sp2-bonded carbon, relative intensities of the bands do not depend on the 458- and 257-nm excitation wavelengths, and a halfwidth and the intensity of the 1600 cm−1 band does not change visibly under pressure at least up to 50 GPa. Bulk modulus of the 2–5-nm nanodiamond determined from the high-pressure study is around 560 GPa. Studied 2–5-nm nanodiamond was purified from contamination layers and dispersed in Si or NaCl