Perovskite structured materials contain myriad tunable ordered phases of electronic and magnetic origin with proven technological importance and strong promise for a variety of energy solutions. An always-contributing influence beneath these cooperative and competing interactions is the lattice, whose physics may be obscured in complex perovskites by the many coupled degrees of freedom, which makes these systems interesting. Here, we report signatures of an approach to a quantum phase transition very near the ground state of the nonmagnetic, ionic insulating, simple cubic perovskite material ScF 3 , and show that its physical properties are strongly effected as much as 100 K above the putative transition. Spatial and temporal correlations in the high-symmetry cubic phase determined using energy-and momentum-resolved inelastic x-ray scattering as well as x-ray diffraction reveal that soft mode, central peak, and thermal expansion phenomena are all strongly influenced by the transition. The class of materials with the perovskite structure and chemical formula ABX 3 contains examples of perhaps every possible type of physical behavior [1,2], much of which is difficult to understand because of the shear complexity of matter. A rich terrain of structural transitions associated with BX 6 octahedral tilting in perovskites strongly effects electronic conduction and magnetic exchange pathways, defining the framework of interactions governing a range of physical properties. The A-site tolerance appears to be an important parameter in determining the structural phase stability [1-3], but stable A-site-free perovskite structures are also thermodynamically stable. These are rare cases among oxides (X = O) because the B ions must take on rare hexavalent (+6) electronic configurations, and the only known instance is ReO 3 . In perovskites based on fluorine (X = F), however, the B ions assume the common trivalent (+3) configuration in an expanded suite of A-site-free perovskite lattices.Figure 1(a) shows a structural phase diagram of BF 3 perovskites, where B is a trivalent metal ion [4]. The 3d metal trifluorides display a reversible [5] structural cubic-torhombohedral (c-r) phase boundary. This sequence of 3d transition metal trifluoride compounds is rhombohedral at room temperature, with the exception of B = Sc, which appears at the zero-temperature terminated c-r phase boundary. Indeed, no rhombohedral phase transition has been observed for ScF 3 down to 0.4 K [6], suggesting that near this composition, the structural phase can be driven by a parameter other than temperature, implying that the ground state of this ionic insulator is very near a quantum phase transition (QPT). Cubic ScF 3 further stands out among substances in that it has the most stable structural phase of any known solid trifluoride, * Corresponding author: jason.hancock@uconn.edu retaining high cubic symmetry and a four-atom unit cell up to its high melting point, >1800 K [6,7]. Separate from the QPT reported here, further interest in this system is due t...

We present a broadband infrared and optical study of the compositionally complex nickel-based superalloy Inconel-718, a common material used in additive manufacturing using the direct metal laser sintering (DMLS) technique. We find a broad, featureless spectral emissivity, which is consistent with dc transport measurements and contextualize the results against literature reports of disordered metals. We show that electronic structure calculations based on first-principles modeling can explain most of the spectral weight distribution and show that the peculiar infrared optical properties in this class of materials can present challenges in accurately reporting remote temperature sensing in DMLS.

Simple cubic 'open' perovskite ScF 3 stands out among trifluoride materials in its large, isotropic negative thermal expansion (NTE), but also its proximity of its zerotemperature state to a structural phase transition. Here we report a temperature and frequencydependent lattice dynamical study of Brillouin zone center lattice excitations of single crystals of ScF 3 using infrared reflectivity measurements. In addition to quantifying the mode strengths and energies in single crystals of this interesting material, we also find strong evidence for multiphonon absorption processes which excite the zoneedge incipient soft modes associated with NTE and the structural quantum phase transition. In this way, we identify an optically allowed pathway to excite soft modes provides a means to athermally populate modes associated with NTE in ScF 3 .

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Strain solitons have been observed statically in several 2D materials and dynamically in substrate materials using ultrafast laser pulses. The latter case relies on lattice relaxation in response to ultrafast heating in a light-absorbing transducer material, a process which is sensitive to the thermal expansion coefficient. Here we consider an unusual case where the sign of the thermal expansion coefficient is negative, a scenario which is experimentally feasible in light of rapid and recent advances in the discovery of negative thermal expansion materials. We present numerical solutions to a nonlinear differential equation which has been repeatedly demonstrated to quantitatively model experimental data and discuss the salient results using realistic parameters for material linear and nonlinear elasticity. The solitons that emerge from the initial value problem with negative and positive thermal expansion are qualitatively different in several ways. The new case of negative thermal expansion gives rise to a nearly-periodic soliton train with chirped profile and free of an isolated shock front. We suggest this unanticipated result may be realized experimentally and assess the potential for certain applications of this generic effect.