Temperature dependence of elastic moduli of polycrystalline β plutonium

Abstract

The elastic moduli of pure polycrystalline beta plutonium were measured over its full range of existence (417 K to 491 K) using resonant ultrasound spectroscopy. The Debye temperature (138 K), Poisson's ratio (0.28), Grüneisen parameter (2.3), and the zerotemperature atomic volume (21.2 Å 3 ) were computed from the measurements. Both bulk and shear moduli decrease smoothly on warming with expected discontinuities at the phase boundaries. The shear modulus is surprisingly nearly the same for beta and gamma Pu. The temperature dependence of bulk moduli for beta Pu is, like gamma Pu, unusually small. Poisson's ratio shows very strong differences among alpha, beta, and gamma Pu indicating they are entirely different metals. The zero-temperature elastic moduli were computed for the three phases as well as for gallium-stabilized delta Pu (also measured by us) and compared to calculations.PACS numbers: 62.20. de, 63.70.+h, 65.40.G-, 62.20.dj

The influence of phonon anharmonicity on thermal and elastic properties of neptunium

“…According to our data at the point of phase transition from a-to b-phase of Np a quite dramatic change of the bulk modulus occurs: b-Np exhibits lower values of the bulk modulus and its weaker temperature depende nce. It is worth noting that the similar changes are observed at the phase transition from a-to b-phase of plutonium [5]. However, in order to verify the results of our calculations , a big amount of experimental data on the bulk modulus of neptunium is required, whereas at the present moment this data is extremely sparse.…”

“…Thus, for palladium and platinum in the entire range of their existence C does not exceed 3.1 [12]. Comparing to plutonium [5] we can point that neptunium possess the values of the Gruneise n parameter, which are typical for d-Pu (C = 3.8 at T = 480 K) but higher than in the case of b-Pu (C = 2.3 at T = 450 K) and c-Pu (C = 1.9 at T = 550 K). This confirms the presence of strong phonon anharmonicity of neptunium.…”

“…It should be noted that the Poisson coefficient r, which strongly affects the Debye temperature and (as a consequence) all thermal and elastic properties, can be determined from either data on elastic modules [5] or on the mean-sq uare displacemen t (MSD) of atoms from the equilibrium positions [12]. However, in the case of Np experimental data neither on elastic modules nor on MSD is available.…”

“…[1][2][3][4][5]) dedicated to investigation of the actinide metals and their compounds. This can be explained not only by their strategic importance, but also by their unusual physical properties.…”

Origin of the multiple configurations that drive the response of δ-plutonium’s elastic moduli to temperature

“…This model could be made to fit δ-Pu's volume versus temperature dependence as measured by elastic neutron scattering for the range of Ga concentrations typically used to stabilize the δ-phase (4). However, measurements of the elastic moduli of polycrystalline Pu-Ga alloys by Suzuki et al (5) showed that the bulk modulus softened substantially on warming in temperature regions where the atomic volume remained fixed. In an attempt to include elastic softening as temperature increased and volume decreased, Lawson et al (1) made the unusual conjecture that the higher energy state with smaller volume, required to get the thermal expansion correct, must make no contribution to the bulk modulus.…”