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Abstract We have investigated the effect of synthesis conditions of BCNO compounds on BN formation and its structural ordering. BCNO compounds were synthesized from boric acid (H 3 BO 3)-melamine (C 3 H 6 N 6) mixtures with various molar ratios (H 3 BO 3 :C 3 H 6 N 6 = 1:1 to 6:1) at 400 °C. The BCNO compounds were then subjected to post heating between 1400 °C and 1800 °C under argon flow. The final products were crystalline BN with hexagonal symmetry exhibiting varying degrees of structural ordering. As the H 3 BO 3 to C 3 H 6 N 6 ratio in the starting composition is increased, BN formation temperature decreases and the structural ordering of BN increases. Post heating at higher temperature also promotes BN formation and structural ordering. The findings indicate that synthesis and structural ordering of BN can be tailored by controlling starting composition and post heating temperature. These observations may provide a guideline to synthesize high or low-density polymorphs of BN at reduced pressure, temperature, or both. Graphical abstract Boron nitrides formed from BCNO compounds exhibited higher degree of structural ordering during post-heating when higher H 3 BO 3 to C 3 H 6 N 6 molar ratios were initially used to synthesize BCNOs. fx1 Highlights • Correlation between BCNO synthesis conditions&BN formation at high temperatures. • Increase in H 3 BO 3 :C 3 H 6 N 6 ratio promotes BN formation and its structural ordering. • Increase in post heating temperature promotes BN formation. • BN synthesis with varied 3-D structural ordering, particle size and morphologies. [ABSTRACT FROM AUTHOR]

Abstract To understand the mechanism of mass transfer during solid state reactions and order-disorder transitions the formation processes of CuAuI and L1 0 -FePd ordered structures at solid state reactions in Cu/Au и Fe/Pd bilayer thin films have been carried out using the method of in situ electron diffraction (ED). The value of the long-range order (LRO) parameter has been estimated for the L1 0 type ordered structures being formed; the order-disorder transition temperatures have been determined. The formation mechanism of the L1 0 type ordered structures formed at the initial stages of the solid state reaction in the Cu/Au and Fe/Pd thin films has been suggested. In the case of Cu/Au it has been shown that the interdiffusion of copper and gold at the initial stage of the solid state reaction results in the reduced size of the grains of the initial materials, as a result, nanocrystalites of the Cu-Au solid solution are formed, and further, grains of the CuAuI ordered solid solution appear and their growth begins. Graphical abstract fx1 Highlights • Solid state reactions in Cu/Au and Fe/Pd bilayer thin films have been investigated. • Structural phase transformations have been studied by in situ ED. • The formation processes of CuAuI and L1 0 -FePd ordered phases have been studied. • The value of the long-range order parameter has been estimated for the ordered structures. • The formation mechanism of the L1 0 type ordered structures has been suggested. [ABSTRACT FROM AUTHOR]

The temperature-dependent behavior of quenched single-crystalline (GeTe) n Sb 2 Te 3 ( n ~2.8, n ~5 and n ~11) was investigated by semiquantitative modeling of diffuse X-ray scattering. The structure at room temperature exhibits trigonal twin domains, each comprising a stacking-disordered sequence of distorted rocksalt-type slabs with variable thicknesses. Ge and Sb share the cation position and vacancies are partially ordered in defect layers (van der Waals gaps) between the slabs. The average structure determined with resonant diffraction data corresponds to a rocksalt-type structure whose cation position is split along the stacking direction. Upon heating, cation ordering leads to a metastable superstructure of the rocksalt type at ~400 °C, which transforms to a rocksalt-type high-temperature phase with randomly distributed cations and vacancies at ~500 °C; this structure was also refined using resonant diffraction. Cooling at high or intermediate rates does not yield the long-range ordered phase, but directly leads to the twinned disordered phase. [ABSTRACT FROM AUTHOR]

We study termination proofs in order to (i) determine computational complexity of programs and (ii) generate efficient programs from the complexity analysis. For this, we construct a termination ordering, called light multiset path ordering (LMPO), which is a restriction of the multiset path ordering. We establish that the class of first order functional programs on lists which is terminating by LMPO characterises exactly the functions computable in polynomial time. [Copyright &y& Elsevier]

Order–disorder structural phase transitions in alkali perchlorates MClO4 (M=Na, K, Rb, Cs) are investigated using molecular dynamics simulation. The potentials in the simulations are based on the Gordon–Kim modified electron gas formalism extended to molecular ions. The simulations yield first-order phase transitions in perchlorates from low temperature orthorhombic structures to high temperature cubic NaCl structures. The perchlorate ions are found to be orientational disordered in the high temperature phases. [Copyright &y& Elsevier]