The 5v 3 bands of 18O enriched ozone: line positions of 16O16O18O, 16O18O16O, 16O18O18O and 18O16O18O

The four 5v ₃ bands of ¹⁸O enriched ozone have been observed and analysed for the first time. Two species (¹⁶O¹⁸O¹⁶O and ¹⁸O¹⁶O¹⁸O) belong to the C_2v symmetry group and two other (¹⁸O¹⁸O¹⁶O and ¹⁶O¹⁶O¹⁸O) to the C_s symmetry group. They have been recorded at a resolution of 0.008 cm^?1 with a pathlength of 32.16 m. Despite the very weak absorptions observed, almost 250 energy levels have been derived for each of the 4 species, with J ? 35 and K _a ? 13, and suitable sets of Hamiltonian parameters have been determined. For 3 species it has been necessary to account for the resonance between the (005) and (311) states to correctly reproduce the spectra observed. These resonances, anharmonic for C_2v, and hybrid (both anhar-monic and Coriolis) for C_s symmetry confirm the accidentally extremely strong coupling between the (005) and (311) states for ¹⁶O₃, due in that case to the very close distance between unperturbed energy levels. This work also confirms the excellent prediction of band centres of these four species derived from the recently determined isotopically invariant molecular potential function.     

Synthesis and thermal stability of cubic ZnO in the salt nanocomposites

Cubic zinc oxide (rs-ZnO), metastable under normal conditions, was synthesized from the wurtzite modification (w-ZnO) at 7.7 GPa and ∼800 K in the form of nanoparticles isolated in the NaCl matrix. The phase transition rs-ZnO → w-ZnO in nanocrystalline zinc oxide under ambient pressure was experimentally studied for the first time by using differential scanning calorimetry and high-temperature X-ray diffraction analysis. It was shown that the transition occurs in the temperature range from 370 to 430 K and its enthalpy at 400 K is −10.2 ± 0.5 kJ mol⁻¹.     

Kinetics of the wurtzite-to-rock-salt phase transformation in ZnO at high pressure

Kinetics of the wurtzite-to-rock-salt transformation in ZnO has been studied in the 5-7 GPa pressure range at temperatures below the activation of diffusion processes. The detailed analysis of non-isothermal experimental data using the general evolution equation describing the kinetics of direct phase transformations in solids allowed us to study the kinetic particularities of both nucleation and growth of the rock-salt phase in parent wurtzite ZnO. The main rate-limiting processes are thermally activated nucleation (E(N) = 383 kJ mol(-1) at 6.9 GPa) and thermally nonactivated (most probably quasi-martensitic) growth (k(G) = 0.833 min(-1) at 6.9 GPa). The high impact of thermal deactivation of nucleation places has been evidenced in the case of slow heating, which indirectly indicates that the rs-ZnO nucleation places are mainly produced by pressure-induced stresses in the parent phase.     

Reduction of the laminar compound of graphite with FeCl3 by hydrogen at high pressure

Conclusions A method is proposed for the reduction of laminar graphite compounds at hydrogen pressure up to 70 kbar, which has a number of significant advantages relative to reported methods. This method may be used to obtain new acceptor LGC.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 450–452, February, 1986.The authors express their gratitude to P. B. Fabrichnyi for assistance in the Moessbauer spectral study of these compounds.     

Thermal phase stability of rhombohedral boron nitride

Abstract

Thermal phase stability of rhombohedra] boron nitride has been studied between 0 and 8 GPa from 300 to 2700 K. Analysis of the data obtained points to the decisive role of kinetic factors in the rBN phase transformations, the structure and dispersity of the samples under study being of great importance. rBN phase transformations in the cBN thermodynamic stability region of the equilibrium p,T phase diagram for boron nitride occur according to Ostwald stepwise principle by the rBN→hBN→(wBN)→cBN scheme.     

hBN ↔ cBN equilibrium line calculated from experimental data on the cBN-to-hBN transformation to 1.4 GPa

Abstract

In the pressure range from 0.3 to 1.4 GPa, the onset temperatures of cBN-to-hBN transformation have been found by quenching method on high-purity single crystals of cubic boron nitride. From the experimental data with allowances made for the kinetics of solid-phase transformation. the hBN?cBN equilibrium line has been calculated, which fits well with the equilibrium phase p, T-diagram of boron nitride.