Pathway bias and emergence of quasi-irreversibility in reversible reaction networks: Extension of Curtin-Hammett principle

可逆な化学反応ネットワークにおける経路選択の原理 --準不可逆性の発現--. 京都大学プレスリリース. 2023-07-21.The Curtin-Hammett principle, which works in a reaction sequence where slow irreversible reactions are connected to a fast reversible reaction, determines the product distribution depending only on the relative energy barriers of the two irreversible reactions, resulting in kinetic pathway selection. A basic question is how the reaction pathway is selected in reaction networks composed of reversible reactions to generate a metastable state. Numerical simulations of model systems where reversible elementary reactions are connected linearly to an initial reversible reaction demonstrate that a metastable state far from equilibrium is transiently produced and that its lifetime is prolonged by increasing the number of connected reversible reactions. The pathway selection in the model systems originates from quasi-irreversibility, and a similar behavior was also observed in the molecular self-assembly of a Pd₆L₄ truncated tetrahedron, which supports the idea that the emergence of quasi-irreversibility is a key general concept underlining kinetic control in reversible reaction networks

Long-range order parameter of single L1₀-FePd nanoparticle determined by nanobeam electron diffraction: Particle size dependence of the order parameter

The long-range order (LRO) parameter (S) of single isolated L 10 -FePd nanoparticle was determined by quantitative analysis of nanobeam electron diffraction (NBD) intensities and intensity calculations considering the multiple scattering of electrons. The obtained order parameters of the nanoparticles larger than 8 nm are distributed around the mean LRO parameter (S- =0.79) which was determined by selected area electron diffraction intensity analysis, while the parameters slightly decreased gradually as the particle size decreased below about 8 nm (S=0.60-0.73). The low degree of order in very small particles is responsible for the coercivity decrease of the L 10 nanoparticles in smaller-sized regions. Quantitative NBD intensity analysis is quite useful for the determination of the LRO parameter of individual L 10 -FePd single crystalline nanoparticle. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed. © 2005 American Institute of Physics.Kazuhisa Sato, Yoshihiko Hirotsu and Hirotaro Mori, "Long-range order parameter of single L1₀-FePd nanoparticle determined by nanobeam electron diffraction: Particle size dependence of the order parameter", Journal of Applied Physics 98, 024308 (2005) https://doi.org/10.1063/1.1985973

Determination of order parameter of L1₀ -FePd nanoparticles by electron diffraction

Long-range order (LRO) parameters of two-dimensional dispersed single-crystalline 10-nm -sized FePd nanoparticles with the L 10 structure have been determined accurately by electron diffraction in transmission electron microscopes (TEMs) under accelerating voltages of 300 kV and 1 kV. Diffraction patterns by exciting hh0 systematic reflections effectively reduced the numbers of diffracted beams and simplified the thickness dependence of intensity ratio I110 I220 for 110 and 220 reflections. Mean thickness of the nanoparticles was estimated to be 7.8 nm by electron holography. The relation between the intensity ratio and the order parameter was calculated on the basis of multiple-scattering intensity calculation. By comparing the relation and experimentally obtained intensity ratios, the order parameters of 0.65 and 0.79 were obtained using 300-kV TEM for FePd nanoparticles after annealing at 873 K for 3.6 and 36 ks, respectively. Also, the order parameter of 0.82 was obtained using 1-MV TEM for the same specimen annealed at 873 K for 36 ks. These order parameters were determined using the Debye-Waller factors for bulk Fe and Pd. The order parameter decreased about 7.3% when a very large Debye-Waller factor as large as 0.01 nm2 was assumed. A combination of electron diffraction under the conditions of hh0 systematic reflections and the diffraction experiment at the high accelerating voltage makes the LRO parameter analysis easy and correct. © 2005 American Institute of Physics.Kazuhisa Sato, Yoshihiko Hirotsu and Hirotaro Mori, "Determination of order parameter of L1₀–FePd nanoparticles by electron diffraction", Journal of Applied Physics 97, 084301 (2005) https://doi.org/10.1063/1.186198