Isotopic Exchange in a Neutron-Irradiated Mixed-Valence Compound: Tl<sub>3</sub>′Tl′′′Cl<sub>6</sub>

Valverde, Serafı́n; Duplâtre, G.

doi:10.1524/ract.1977.24.23.121

Cited by 5 publications

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“…In a series of experiments [3][4][5][6][7][8], we have undertaken to unravel the mechanism of exchange between thallium atoms in a mixed-valence compound, Tl|Tl ni Cl 6 , by combining radiochemical analysis and physical techniques, conductivity and positron lifetime spectroscopy [7,8].…”

Section: Introductionmentioning

confidence: 99%

“…The most salient observations were as follows: (i) in the 204 Tl-labelled material, exchange proceeds at moderate temperatures, roughly between 470 Κ and 550 K, and is affected neither by changing the atmosphere (either in air or in vacuo), nor by producing extrinsic atomic defects when irradiating the samples with γ-rays prior to heating [3]; (ii) local disorder generated by recoiling 204 η atoms has no influence, since exchange proceeds in exactly the same way in labelled or in neutron-irradiated samples [4]; (iii) on the contrary, exchange occurs at lower temperatures, when probed with 208 T1 atoms implanted into the crystals [5]; (iv) intrinsic mobile cation vacancies are produced with a low formation energy in T1 4 C1 6 [7];…”

Section: Introductionmentioning

confidence: 99%

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Isotopic Exchange Reaction Kinetics in Mixed-Valence TI₄CI₆

Fernández-Valverde¹,

Duplâtre

1989

Radiochimica Acta

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Kinetics new to the field of isotopic exchange in solids and based on diffusion controlled reactions are applied to isochronal and isothermal data obtained in a radiochemical study of two batches of ,04 Tl-labelled mixed-valence T1 4 C1 6 , consisting of either untreated or of crushed crystals. The exchange between Tl 1 and Tl m is shown to be faster in the latter samples. On the basis of previous results, suggesting that exchange would be triggered by the diffusion of anion vacancies, two models are probed, implying either the presence of two regions in the lattices (surfaces and dislocations as opposed to the bulk) or of two populations of vacancies (extrinsic and intrinsic). The mathematical expressions used allow a very good fitting of the data, much better than what is obtained with the classical MACKAY equations. However, in either case all derived parameters have quite acceptable values on physical grounds, except the reaction radius which appears to be too large, at a few nm. Ignoring this anomaly, the main difference between untreated and crushed crystals appears to be a lower apparent activation energy for diffusion in the latter, ascribable to the presence of strains in the lattice; a minor difference would arise from either a larger proportion of the disordered regions or a larger extrinsic vacancy concentration in the crushed samples, although both properties would contribute only to a few percents in the overall exchange process.

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