There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Most of the research is centred on large magnetocaloric effects and large electrocaloric effects, but the former require large magnetic fields that are challenging to generate economically and the latter require large electric fields that can only be applied without breakdown in thin samples. Here we use small changes in hydrostatic pressure to drive giant inverse barocaloric effects near the ferrielectric phase transition in ammonium sulphate. We find barocaloric effects and strengths that exceed those previously observed near magnetostructural phase transitions in magnetic materials. Our findings should therefore inspire the discovery of giant barocaloric effects in a wide range of unexplored ferroelectric materials, ultimately leading to barocaloric cooling devices.

/pdf/giant-barocaloric-effects-at-low-pressure-in-ferrielectric-22u5kpucus.pdf

Giant barocaloric effects at low pressure in ferrielectric ammonium sulphate

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2–7 m, while providing data at sub-mm to mm scales. We report on SuperCam’s science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.

/pdf/the-supercam-instrument-suite-on-the-mars-2020-rover-science-2ss3m5owmk.pdf

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

A luminescence database for minerals and materials has been complied from the literature, the aim being to create a resource that will aid in the analysis of luminescence spectral of ionic species in minerals and materials. The database is based on a range of excitation techniques and records both major and minor lines, and their activators. The luminescence techniques included in the database are cathodoluminescence, ion luminescence, and photoluminescence. When combined with other traditional X-ray measurements collected on the same region, use of the luminescence database will give additional insight into the chemistry of minerals and materials.

/pdf/luminescence-database-i-minerals-and-materials-19sr3ou4xi.pdf

Luminescence Database I—Minerals and Materials

In this Letter, we address the long-range interaction between kinks and antikinks, as well as kinks and kinks, in φ^{2n+4} field theories for n>1. The kink-antikink interaction is generically attractive, while the kink-kink interaction is generically repulsive. We find that the force of interaction decays with the 2n/(n-1)th power of their separation, and we identify the general prefactor for arbitrary n. Importantly, we test the resulting mathematical prediction with detailed numerical simulations of the dynamic field equation, and obtain good agreement between theory and numerics for the cases of n=2 (φ^{8} model), n=3 (φ^{10} model), and n=4 (φ^{12} model).

Kink-Kink and Kink-Antikink Interactions with Long-Range Tails.

Brillouin spectroscopy was used to study the elastic properties of ferroelastic ${\mathrm{LiCsSO}}_{4}$. The sound velocities, linewidths, and intensities of twelve acoustic modes were measured in the temperature range from 150 to 293 K. The mmm (${D}_{2h}$)\ensuremath{\rightarrow}2/m (${C}_{2h}$) phase-transition temperature was found to be 202 K. All nonzero components of the elastic stiffness tensor of the high-temperature phase were determined. The frequency, linewidth, and integrated intensity of the Brillouin line associated with the soft acoustic mode (characterized by ${c}_{66}$) were found to be strongly temperature dependent in the vicinity of ${T}_{c}$. In order to explain all experimental features, the fourth-order Landau free-energy expansion in all strain components was carried out. Using a non-Gaussian approach to critical fluctuations, the effective interaction range was calculated to be \ensuremath{\sim}10 nm.

Brillouin scattering studies of the ferroelastic phase transition in LiCsSO4.

High-resolution Brillouin spectroscopy was used to study the elastic properties of ferroelastic ${\mathrm{K}}_{3}$Na(${\mathrm{SeO}}_{4}$${)}_{2}$. The temperature dependence of nine Brillouin modes of the acoustic phonons propagating in the [100], [010], [001], and [011] directions were measured in the temperature range 290--380 K. These results indicate a 3\ifmmode\bar\else\textasciimacron\fi{}m\ensuremath{\rightarrow}2/m transition at ${\mathit{T}}_{\mathit{c}}$=334 K followed, by approximately 12 K, by a transition involving an unknown mode Q. Mode softening in the ${\mathit{c}}_{66}$ and ${\mathit{c}}_{44}$ elastic constants results from the main first-order transition while an additional softening in ${\mathit{c}}_{33}$ and ${\mathit{c}}_{44}$ is due to coupling with Q. A Landau-type free-energy expansion has been postulated and discussed in order to explain the qualitative features of the system.

Ferroelastic phase transition in K3Na(CrO4)2: Brillouin scattering studies and theoretical modeling.

Brillouin spectroscopy was used to study surface acoustic waves on a supported layer of (111)‐oriented porous silicon having a thickness of 2.7 μm and a porosity of 30%. The Rayleigh surface wave velocities were found to be significantly lower than corresponding velocities for crystalline silicon. A complete set of elastic constants for the porous layer was determined from the measured directional dependence of the surface wave velocity in the (111) plane. The best‐fit constants are C11=56.0±0.7 GPa, C12=6.7±0.3 GPa and C44=37.0±0.8 GPa. The anisotropy factor, η=1.50 indicates that the porous layer is elastically anisotropic.

Elastic characterization of a supported porous silicon layer by Brillouin scattering

High-resolution Brillouin spectroscopy was used to study the elastic properties of Rb4LiH3(SO4)4 and K4LiH3(SO4)4 crystals. In contrast to earlier studies of the former compound, the present results indicate that the ferroelastic phase transition, which occurs at approximately 115 K, is of the 4 to 2 type rather than 4 mm to mm2 as previously believed. An appropriate theoretical model using a two-component order parameter free energy expansion has been presented based on the Landau theory. K4LiH3(SO4)4 does not appear to be ferroelastic in the temperature range examined and only exhibits a slight change in slope of the temperature plots for elastic constants associated with longitudinal phonons.

http://iopscience.iop.org/article/10.1088/0953-8984/3/30/001/pdf

Elastic properties of Rb4LiH3(SO4)4 and K4LiH3(SO4)4

High-resolution Brillouin spectroscopy was used to investigate the elastic properties of $[{\mathrm{NH}}_{3}{(\mathrm{C}\mathrm{H}}_{3}{)]}_{5}{\mathrm{Bi}}_{2}{\mathrm{Cl}}_{11}.$ The temperature dependences of nine phonon modes propagating in the directions [100], [010], [001], [110], [101], and [011] were obtained in the temperature range from 120 to 330 K. Strong correlations were found with the electric polarization mode which exhibits anomalous behavior at 307 and 170 K. A theoretical explanation of the experimental observations was given in terms of Landau-type free energy expansion for two inequivalent sublattices. Discussion was provided regarding the possible types of couplings between strain tensor components and spontaneous polarization.

M. J. Clouter

Papers

Brillouin scattering studies of the ferroelastic phase transition in LiCsSO4.

Ferroelastic phase transition in K3Na(CrO4)2: Brillouin scattering studies and theoretical modeling.

Elastic characterization of a supported porous silicon layer by Brillouin scattering

Elastic properties of Rb4LiH3(SO4)4 and K4LiH3(SO4)4

Brillouin-scattering studies of ferroelectric [ NH 3 ( C H 3 ) ] 5 Bi 2 Cl 11