Tuneable correlated disorder in alloys

Abstract

Understanding the role of disorder, and the correlations that exist within it, is one of the defining challenges in contemporary materials science. However, there are few material systems, devoid of other complex interactions, that can be used to systematically study the effects of crystallographic conflict on correlated disorder. Here, we report extensive diffuse x-ray scattering studies on the epitaxially stabilized alloy U 1−x Mo x , showing that a new form of intrinsically tuneable correlated disorder arises from a mismatch between the preferred symmetry of a crystallographic basis and the lattice upon which it is arranged. Furthermore, combining grazing incidence inelastic x-ray scattering and state-of-the-art ab initio molecular dynamics simulations, we discover strong disorder-phonon coupling. This breaks global symmetry and dramatically suppresses phonon lifetimes compared to alloying alone, providing an additional design strategy for phonon engineering. These findings have implications wherever crystallographic conflict can be accommodated, and they may be exploited in the development of future functional materials.

Synchrotron Radiation Techniques and their Application to Actinide Materials

“…These materials have been of interest for many years, and might find applications as advanced nuclear fuels, but single crystals are not available and there has been controversy over whether the structures are body-centered cubic (bcc) or something more complicated. Growing epitaxial films turned out to be relatively simple, and the subsequent diffuse scattering patterns (Chaney et al, 2021) showed that the structure is essentially bcc but superposed on that symmetry is correlated disorder, where the local symmetry is lower, as if the uranium atoms prefer to have neighbors reminiscent of the low symmetry found in the element at room temperature, and not the high symmetry demanded of bcc. The correlation length of such disorder depends on the composition, but is of the order of 5-10 nm.…”

Correlated disorder as a way towards robust superconductivity

“…Effects related to the disorder correlations have been experimentally observed in gases of cold atoms 38,39 and photonic systems 40 . Also, correlated deviations from the ideal periodicity of a crystal structure plays a significant role for functional materials 41 that utilize ionic conductivity 42 and their ferroelectric 43,44 , thermoelectric 45 , and photoelectric properties 46 . Achieving desired functionalities by manipulating patterns of the structural disorder is one of the goals of contemporary material science studying disordered crystals 33,47 .…”

Mode-coupling theory of lattice dynamics for classical and quantum crystal

“…It is interesting to also consider static properties associated with the formalism, in particular the quasiparticle frequencies. Interestingly, these temperature-dependent frequencies have often been compared with great success to experiments 35,37,43 , but these comparisons lacked a rigorous theoretical justification. It has been proposed to interpret these frequencies as an approximation of the first excitation of the system 49,75 .…”

“…The goal of this procedure is to minimize the importance of high order contributions compared to the effective harmonic one. By using perturbation theory on top of this effective anharmonic Hamiltonian, TDEP has proven its ability to describe anharmonic properties with a great number of applications on the free energy and transport of materials [37][38][39][41][42][43] . Unfortunately, the renormalized anharmonic Hamiltonian at the heart of TDEP lacks a theoretical justification.…”