Cosmic composites: Rocks from space and their astonishing influence on earth and humanity

Meteorites are some of the most complex natural materials known. They are incredibly compositionally diverse rocks, ranging from chunks of almost pure iron and nickel metal, which derive from the cores of disrupted planetary bodies, to pristine collections of dust and ice that have existed virtually umolested since the birth of the Sun. Certain types of meteorites contain the oldest materials ever dated, and some even host the direct remnants of previous generations of stars that contributed material to build our Solar System. Meteorites are time capsules of information about Solar System history and evolution, and, simply put, are a scientific treasure trove. In addition, whereas most meteorites come from the scores of planetary bodies that now reside in the asteroid belt, some even represent samples that originate directly from our Moon and Mars. However, although the value of information we have gained about Earth and the Solar System from studying meteorites as scientific objects cannot be underestimated, the principal importance of meteorites to humanity is far more complex due to their oftentimes spectacular arrivals and important payloads. From a cultural perspective, many of the world’s ancient empires and most popular religions have inflection points in which meteorites played an important role, in some cases drastically altering the course of history. Christianity was an obscure cult followed by relatively few people until a timely meteoritic interaction changed its trajectory. The most venerated object in the Islamic faith almost certainly has a meteoritic origin, and for a short time, worship of a meteorite (adorned with fancy dressings and gemstones) was even the official religion of the Roman Empire. Wars have been waged (and ended) due to encounters with extraterrestrial materials. Temples have been built to honor fallen stones, and early cultures were enamored by the metal found in meteorites, as they did not yet know how to produce such metal themselves. These numerous overlaps between humans and meteorites were critical in shaping modern culture around the world, yet the most important contributions of meteorites to Earth started happening shortly after the planet formed ~4.5 billion years ago. If meteorites had not interacted with the Earth shortly after its formation, the Moon would not exist. Earth likely would not have liquid water at its surface or offer a habitable atmosphere. The continued bombardment of Earth by space rocks gives humans access to many of the precious metals crucial for modern technology—such as iridium, platinum, and gold—which would otherwise be thoroughly sequestered in Earth’s core and inaccessible for exploitation. In addition, and probably most importantly, meteorites were the primary delivery vehicles for the complex organic materials that eventually created the biosphere. Many of the organic building blocks thought essential for the emergence of life are present in primitive meteorites, with one sample alone hosting over 80 amino acids (known life uses only 20 of these). In addition, multiple nucleotide bases of both RNA and DNA as well as other vital biomolecules have been discovered in extraterrestrial specimens, indicating that the building blocks of life could have been created abiotically in the outer Solar System and delivered to Earth via meteorites. And, of course, a meteorite impact was influential to ending the long reign of the dinosaurs, paving the way for mammals to rapidly evolve and thrive, promptly taking over the helm as Earth’s dominant class of creature. In this presentation, I will discuss the immense influence meteorites have had on our planet, spanning from its creation to modern human culture. In addition, I will highlight some of the incredible scientific insights we have gained from the study of these unique materials, and some of the active areas of research in reconstructing the history and evolution of our Solar System

Perovskite nitrides: A new playground for functional materials

The perovskite crystal is a favorite playground for electroceramists across a wide variety of applications, and recent developments on hybrid metallorganic perovskite photovoltaics has renewed interest in expanding the chemical space of this flexible and multifunctional crystal structure. A survey of experimentally confirmed simple perovskite compounds (ABX3) finds no reports of pure X=N anion chemistries. One challenge of forming nitride perovskite materials is the high valence cations needed to satisfy the high valency of nitrogen; another is limiting oxygen impurities. Computational predictions of energetically favorable nitride perovskites have been reported[1] and DFT+LDA methods[2] suggest that the lowest energy state of LaWN3 is a non-centrosymmetric R3c type distorted perovskite structure with a spontaneous polarization of approximately 60µC/cm2 along the \u3c111\u3e polar axis. A relatively low energy barrier predicted for polarization reversal raises the possibility of ferroelectricity as well. Developing a ferroelectric nitride would greatly simplify integration of a number of functional (e.g., ferroelectric, piezoelectric, and more) properties directly with nitride semiconductors for a variety of integrated sensing and energy conversion applications. Here we report the experimental confirmation of oxygen-free LaWN3 as a perovskite (Fig. 1) using multiple fabrication approaches. Calculations show 5 different symmetries with very similar lattice energies (3 polar and 2 non-polar); refinements of x-ray and electron diffraction in conjunction with property measurements document the complexity of the LaWN3 system in addition to other closely-related perovskite nitrides. [1] R. Sarmiento-Pérez et. al., Chemistry of Materials, 27, 5957 (2015) [2] Y. Fang et. al., Physical Review B,95, 014111 (2017) Please click Additional Files below to see the full abstract

Chemical heterogeneity in electroceramics: The good, the bad, and the difficult to characterize

As characterization techniques continue to advance, the materials community is reminded again and again that our samples are not as perfect as we generally describe them to be. This presentation will focus on Bi(Zn0.5Ti0.5)O3–BaTiO3-based ceramics in which subtle mesoscale cation gradients have been identified as a key factor in the phenomenal temperature- and field-stable permittivity of these unusual dielectrics as well as their remarkably high resistivity values and associated activation energies.[1,2] Earlier work has shown that the single perovskite phase that results after calcination of mixed oxides and carbonates is formed through a complex series of solid-state reactions (Figure 1),[3] and complementary sintering studies have strongly suggested that development of these complex microstructures with mesoscale heterogeneity is strongly dependent upon cation diffusion kinetics (Figure 2). Here, we report on the effects of reaction pathways during calcination on phase formation and microstructural development during sintering in ceramics of nominally identical xBi(Zn0.5Ti0.5)O3 – (1-x)BaTiO3 compositions. These results remind us once again that while often treated as such, material micro/meso/nanostructure is not a state function, and that local ion environments can be determined by processing steps, which can in turn profoundly and selectively affect phase formation, ion diffusion, microstructure development, and resultant properties. This reinforces the need for multiple complementary characterization and measurement techniques for effective description of complex functional materials, and provides a cautionary tale for the budding age of computational materials discovery that real materials—and occasionally enabling performance—often live outside the realm of thermodynamic equilibrium

Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions

Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years