Non-d0d^0 Mn-driven ferroelectricity in antiferromagnetic BaMnO3_3

Using first-principles density functional theory we predict a ferroelectric ground state -- driven by off-centering of the magnetic Mn$^{4+}$ ion -- in perovskite-structure BaMnO$_3$. Our finding is surprising, since the competition between energy-lowering covalent bond formation, and energy-raising Coulombic repulsions usually only favors off-centering on the perovskite $B$-site for non-magnetic $d^0$ ions. We explain this tendency for ferroelectric off-centering by analyzing the changes in electronic structure between the centrosymmetric and polar states, and by calculating the Born effective charges; we find anomalously large values for Mn and O consistent with our calculated polarization of 12.8 $\mu$C/cm$^2$. Finally, we suggest possible routes by which the perovskite phase may be stabilized over the usual hexagonal phase, to enable a practical realization of a single-phase multiferroic.Comment: 6 pages, 3 figure

Strain-controlled band engineering and self-doping in ultrathin LaNiO3_3 films

We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to those of bulk hole-doped superconducting cuprates with varying doping level. Density functional calculations reveal that the strain-induced changes in the transport properties are due to self-doping in the low-energy electronic band structure. The results imply that thin-film epitaxy can serve as a new means to achieve hole-doping in other (negative) charge-transfer gap transition metal oxides without resorting to chemical substitution

New Developments in Tellurite Glass Fibers

Recent developments on the manufacture of tellurite glass fibers are presented. Technical issues related to glass synthesis, preform manufacturing and fiber drawing as well as prospective of commercial exploitation are discussed

Computationally Directed Discovery of MoBi\u3csub\u3e2\u3c/sub\u3e

Incorporating bismuth, the heaviest element stable to radioactive decay, into new materials enables the creation of emergent properties such as permanent magnetism, superconductivity, and nontrivial topology. Understanding the factors that drive Bi reactivity is critical for the realization of these properties. Using pressure as a tunable synthetic vector, we can access unexplored regions of phase space to foster reactivity between elements that do not react under ambient conditions. Furthermore, combining computational and experimental methods for materials discovery at high-pressures provides broader insight into the thermodynamic landscape than can be achieved through experiment alone, informing our understanding of the dominant chemical factors governing structure formation. Herein, we report our combined computational and experimental exploration of the Mo–Bi system, for which no binary intermetallic structures were previously known. Using the ab initio random structure searching (AIRSS) approach, we identified multiple synthetic targets between 0–50 GPa. High-pressure in situ powder X-ray diffraction experiments performed in diamond anvil cells confirmed that Mo–Bi mixtures exhibit rich chemistry upon the application of pressure, including experimental realization of the computationally predicted CuAl2-type MoBi2 structure at 35.8(5) GPa. Electronic structure and phonon dispersion calculations on MoBi2 revealed a correlation between valence electron count and bonding in high-pressure transition metal–Bi structures as well as identified two dynamically stable ambient pressure polymorphs. Our study demonstrates the power of the combined computational–experimental approach in capturing high-pressure reactivity for efficient materials discovery

Análise da Proposta Federal de Implementação da Avaliação Ambiental Estratégica no Brasil

Strategic Environmental Assessment (SEA) is a process that makes environmental issues be considered in strategic decisions. After 2000, there was a global spread of this practice, and many countries already have regulations. Brazil is still in the stage of implementation proposals of this instrument. Thus, this study aims to investigate whether the guidelines formulated for SEA practice meet a set of factors that make the system to be deployed point to a more conducive way to the effectiveness of its action. To this end, we used the Fischer (2007) method with adaptations. The results indicate, as positive aspects of the proposal, the definition of the SEA goal and the predicted society participation in the process and, as its weaknesses, the lack of definition of responsibilities and procedures to be followed. From the conclusion that the text of the draft needs to be improved, international experience must be considered to avoid mistakes and maximise SEA gains.La Evaluación Ambiental Estratégica (EAE) es un proceso que procura que los temas ambientales sean considerados en decisiones estratégicas (políticas, planos y programas). A partir del año 2000 su práctica se difundió a nivel mundial, lo cual permitió que muchos países cuenten actualmente con regulaciones de esta herramienta. El contexto Brasilero aún se encuentra en la etapa de proponer la implementación de este instrumento. Así, el objetivo de este trabajo es indagar si las directrices que se están formulando para la práctica de la EAE cumplen con una serie de requerimientos que puedan permitir que el nuevo sistema inicie un camino hacia la implementación eficaz en el momento de la ejecución.  Para este fin, se utilizó el método propuesto por Fischer (2007), con algunos ajustes. Los resultados indicaron como aspectos positivos de la propuesta: la definición del objetivo de la EAE y la consideración de la participación de la sociedad durante el proceso; y como debilidades: la falta de definición de responsabilidades y de los procedimientos a seguir. Se concluye que el texto de la minuta necesita ser mejorado, y que sería interesante considerar la experiencia internacional para evitar errores y maximizar los beneficios de la EAE.A avaliação ambiental estratégica (AAE) é um processo que faz com que questões ambientais sejam consideradas em decisões estratégicas (políticas, planos e programas). Após 2000, ocorreu a disseminação mundial da prática, sendo que diversos países já contam com regulamentação específica. O Brasil ainda está na etapa de propostas de implementação deste instrumento. Este trabalho objetiva averiguar se as diretrizes que estão sendo formuladas para a prática da AAE atendem a um conjunto de fatores que façam com que o sistema a ser implantado aponte para um caminho mais propício à efetividade de sua ação. Para este fim, foi adaptado o método proposto por Fischer (2007). Os resultados apontam como aspectos positivos da proposta a definição do objetivo da AAE e a previsão de participação da sociedade no processo e, como fraquezas, a falta de definição de responsabilidades e dos procedimentos a serem seguidos. A partir da conclusão de que o texto da minuta precisa ser melhorado, a experiência internacional precisa ser considerada para evitar erros cometidos e potencializar os ganhos da AAE