First-Principles Thermodynamics of Coherent Interfaces in Samarium-Doped Ceria Nanoscale Superlattices

Nanoscale superlattices of samarium-doped ceria layers with varying doping levels have been recently proposed as a novel fuel cell electrolyte. We calculate the equilibrium composition profile across the coherent {100} interfaces present in this system using lattice-gas Monte Carlo simulations with long-range interactions determined from electrostatics and short-range interactions obtained from ab initio calculations. These simulations reveal the formation of a diffuse, nonmonotonic, and surprisingly wide (11 nm at 400 K) interface composition profile, despite the absence of space charge regions

First-principles thermodynamic modeling of lanthanum chromate perovskites

Tendencies toward local atomic ordering in (A,A′)(B,B′)O_(3−δ) mixed composition perovskites are modeled to explore their influence on thermodynamic, transport, and electronic properties. In particular, dopants and defects within lanthanum chromate perovskites are studied under various simulated redox environments. (La_(1−x),Sr_x)(Cr_(1−y),Fe_y)O_(3−δ) (LSCF) and (La_(1−x),Sr_x)(Cr_(1−y),Ru_y)O_(3−δ) (LSCR) are modeled using a cluster expansion statistical thermodynamics method built upon a density functional theory database of structural energies. The cluster expansions are utilized in lattice Monte Carlo simulations to compute the ordering of Sr and Fe(Ru) dopant and oxygen vacancies (Vac). Reduction processes are modeled via the introduction of oxygen vacancies, effectively forcing excess electronic charge onto remaining atoms. LSCR shows increasingly extended Ru-Vac associates and short-range Ru-Ru and Ru-Vac interactions upon reduction; LSCF shows long-range Fe-Fe and Fe-Vac interaction ordering, inhibiting mobility. First principles density functional calculations suggest that Ru-Vac associates significantly decrease the activation energy of Ru-Cr swaps in reduced LSCR. These results are discussed in view of experimentally observed extrusion of metallic Ru from LSCR nanoparticles under reducing conditions at elevated temperature

First-principles thermodynamic modeling of atomic ordering in yttria-stabilized zirconia

Yttria-stabilized zirconia YSZ is modeled using a cluster expansion statistical thermodynamics method built upon a density-functional theory database. The reliability of cluster expansions in predicting atomic ordering is explored by comparing with the extensive experimental database. The cluster expansion of YSZ is utilized in lattice Monte Carlo simulations to compute the ordering of dopant and oxygen vacancies as a function of concentration. Cation dopants show a strong tendency to aggregate and vacate significantly sized domains below 9 mol % Y_2O_3, which is likely important for YSZ aging processes in ionic conductivity. Evolution of vibrational and underlying electronic properties as a function of Y doping is explored

Measurement and Control of Single Nitrogen-Vacancy Center Spins above 600 K

We study the spin and orbital dynamics of single nitrogen-vacancy (NV) centers in diamond between room temperature and 700 K. We find that the ability to optically address and coherently control single spins above room temperature is limited by nonradiative processes that quench the NV center's fluorescence-based spin readout between 550 and 700 K. Combined with electronic structure calculations, our measurements indicate that the energy difference between the 3E and 1A1 electronic states is approximately 0.8 eV. We also demonstrate that the inhomogeneous spin lifetime (T2*) is temperature independent up to at least 625 K, suggesting that single NV centers could be applied as nanoscale thermometers over a broad temperature range.Comment: 8 pages, 5 figures, and 14 pages of supplemental material with additional figures. Title change and minor revisions from previous version. DMT and DJC contributed equally to this wor

Self-driven lattice-model Monte Carlo simulations of alloy thermodynamic

Monte Carlo (MC) simulations of lattice models are a widely used way to compute thermodynamic properties of substitutional alloys. A limitation to their more widespread use is the difficulty of driving a MC simulation in order to obtain the desired quantities. To address this problem, we have devised a variety of high-level algorithms that serve as an interface between the user and a traditional MC code. The user specifies the goals sought in a high-level form that our algorithms convert into elementary tasks to be performed by a standard MC code. For instance, our algorithms permit the determination of the free energy of an alloy phase over its entire region of stability within a specified accuracy, without requiring any user intervention during the calculations. Our algorithms also enable the direct determination of composition-temperature phase boundaries without requiring the calculation of the whole free energy surface of the alloy system

First-principles theory of the luminescence lineshape for the triplet transition in diamond NV centre

In this work we present theoretical calculations and analysis of the vibronic structure of the spin-triplet optical transition in diamond nitrogen-vacancy centres. The electronic structure of the defect is described using accurate first-principles methods based on hybrid functionals. We devise a computational methodology to determine the coupling between electrons and phonons during an optical transition in the dilute limit. As a result, our approach yields a smooth spectral function of electron-phonon coupling and includes both quasi-localized and bulk phonons on equal footings. The luminescence lineshape is determined via the generating function approach. We obtain a highly accurate description of the luminescence band, including all key parameters such as the Huang-Rhys factor, the Debye-Waller factor, and the frequency of the dominant phonon mode. More importantly, our work provides insight into the vibrational structure of nitrogen vacancy centres, in particular the role of local modes and vibrational resonances. In particular, we find that the pronounced mode at 65 meV is a vibrational resonance, and we quantify localization properties of this mode. These excellent results for the benchmark diamond nitrogen-vacancy centre provide confidence that the procedure can be applied to other defects, including alternative systems that are being considered for applications in quantum information processing

Vibrational thermodynamics: coupling of chemical order and size effects

The effects of chemical order on the vibrational entropy have been studied using first-principles and semi-empirical potential methods. Pseudopotential calculations on the Pd_3V system show that the vibrational entropy decreases by 0.07k_B upon disordering in the high-temperature limit. The decrease in entropy contradicts what would be expected from simple bonding arguments, but can be explained by the influence of size effects on the vibrations. In addition, the embedded-atom method is used to study the effects of local environments on the entropic contributions of individual Ni and Al atoms in Ni_3Al. It is found that increasing numbers of Al nearest neighbours decreases the vibrational entropy of an atom when relaxations are not included. When the system is relaxed, this effect disappears, and the local entropy is approximately uniform with increasing number of Al neighbours. These results are explained in terms of the large size mismatch between Ni and Al. In addition, a local cluster expansion is used to show how the relaxations increase the importance of long-range and multisite interactions

Consumer Perception of Bread Quality

Bread contains a wide range of important nutritional components which provide a positive effect on human health. However, the consumption of bread in Belgium is declining during the last decades. This is due to factors such as changing eating patterns and a increasing choice of substitutes like breakfast cereals and fast foods. The aim of this study is to investigate consumer’s quality perception of bread towards sensory, health and nutrition attributes. Consumer’s quality perception of bread seams to be determined by sensory and health attributes. Three clusters of consumers are identified based on these attributes. In the first cluster, consumers’ quality perception of bread is not dependent on the health attributes it embraces, but to some extent on sensory attributes. For the second cluster, both health and sensory attributes appear to influence quality perception. In the third cluster only sensory attributes appear to be important in determining quality perception, though in a negative direction. The results of this study will possibly help health professionals and policy makers to systematically inform the consumers about the positive effects of bread and its components. Furthermore, firms can use the result to build up a tailor-made marketing strategy.Consumer, Quality perception, Bread, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety,