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The exercises described here conveniently exploit the built-in acceleration sensors in smartphones, devices that are becoming ubiquitous if not essential items for most students. This allows each student to have the opportunity for a hands-on experience and to collect their own data, reduces preparation time, and greatly reduces cost by removing the need of purchasing a gravimeter to perform the same or similar tasks in gravity surveys. These exercises further demonstrate the educational value of using smartphones as scientific tools and that freely available accelerometer software applications operate with acceptable tolerance. The differences between accelerometers placed in smartphones and gravimeters are further discussed in the companion paper, “Part 1: Smartphone Applications for Gravitational Acceleration Surveys.”

There is a considerable amount of literature on the electrical resistivity of iron at Earth’s core conditions, while only few studies have considered iron and iron-alloys at other planetary core conditions. Much of the total work has been carried out in the past decade and a review to collect data is timely. High pressures and temperatures can be achieved with direct measurements using a diamond-anvil cell, a multi-anvil press or shock compression methods. The results of direct measurements can be used in combination with first-principle calculations to extrapolate from laboratory temperature and pressure to the relevant planetary conditions. This review points out some discrepancies in the electrical resistivity values between theoretical and experimental studies, while highlighting the negligible differences arising from the selection of pressure and temperature values at planetary core conditions. Also, conversions of the reported electrical resistivity values to thermal conductivity via the Wiedemann-Franz law do not seem to vary significantly even when the Sommerfeld value of the Lorenz number is used in the conversion. A comparison of the rich literature of electrical resistivity values of pure Fe at Earth’s core-mantle boundary and inner-core boundary conditions with alloys of Fe and light elements (Si, S, O) does not reveal dramatic differences. The scarce literature on the electrical resistivity at the lunar core suggests the effect of P on a wt% basis is negligible when compared to that of Si and S. On the contrary, studies at Mercury’s core conditions suggest two distinct groups of electrical resistivity values but only a few studies apply to the inner-core boundary. The electrical resistivity values at the Martian core-mantle boundary conditions suggest a negligible contribution of Si, S and O. In contrast, Fe-S compositions at Ganymede’s core-mantle boundary conditions result in large deviations in electrical resistivity values compared to pure Fe. Contour maps of the reported values illustrate ρ(P, T) for pure Fe and its alloys with Ni, O and Si/S and allow for estimates of electrical resistivity at the core-mantle boundary and inner-core boundary conditions for the cores of terrestrial-like planetary bodies.

Geodesy is a very active and essential research discipline in geophysics but it is not a commonly studied subject at the secondary school or junior post-secondary levels. Far more frequently, gravity and gravitational acceleration are discussed, to some extent, in elementary kinematics or classical mechanics courses. This often takes the form of the force acting on a body or bodies due to gravity, or that the acceleration (agrav) of a free-falling body is 9.8(1) m/s2—which implies the setting of the question is at Earth’s surface. While the latter is a reasonable and practical approximation, agrav observed over the surface of Earth varies and is dependent on several factors. These are normally related to elevation and latitude variations caused by Earth’s rotation. Earth’s rotation contributes negatively to agrav at the equator due to the centrifugal force outward and equatorial bulge, which makes the equatorial radius larger than the polar radius. Offsetting this partially is the positive contribution to agrav at the equator caused by the equatorial bulge because of the extra mass comprising the bulge.

Recent theoretical studies have tried to constrain Mercury’s internal structure and composition using thermal evolution models. The presence of a thermally stratified layer of Fe-S at the top of an Fe-Si core has been suggested, which implies a sub-adiabatic heat flow on the core side of the CMB. In this work, the adiabatic heat flow at the top of the core was estimated using the electronic component of thermal conductivity (kel), a lower bound for thermal conductivity. Direct measurements of electrical resistivity (ρ) of Fe-8.5wt%Si at core conditions can be related to kel using the Wiedemann-Franz law. Measurements were carried out in a 3000 ton multi-anvil press using a 4-wire method. The integrity of the samples at high pressures and temperatures was confirmed with electron-microprobe analysis of quenched samples at various conditions. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of ρ at melting seem to remain constant at 127 µΩ·cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury’s core-mantle boundary is estimated between 21.8-29.5 mWm-2, considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury’s dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core. Simply considering the internal structure of Mercury, these results support the capture of Mercury into a 3:2 resonance orbit during the thermally driven era of the dynamo.

The isostructural dimers of the 1,4-phenylene-bridged bis-1,2,3,5-dithia- and bis-1,2,3,5-diselenadiazolyl diradicals 1,4-S/Se are small band gap semiconductors. The response of their molecular and solid state electronic structures to pressure has been explored over the range 0-10 GPa. The crystal structures, which consist of cofacially aligned (pancake) π-dimers packed into herringbone arrays, experience a continuous, near-isotropic compression. While the intramolecular covalent E-E (E = S/Se) bonds remain relatively unchanged with pressurization, the intradimer E···E separations are significantly shortened. Molecular and band electronic structure calculations using density functional theory methods indicate that compression of the π-dimers leads to a widening of the gap Δ E between the highest occupied and lowest unoccupied molecular orbitals of the dimer, an effect that offsets the expected decrease in the valence-to-conduction band gap E

Magnetism is traditionally taught within the subject of electromagnetism at the undergraduate and graduate levels in physics courses, with the goal of establishing a solid foundation of the underlying physical mechanisms before advancing to more specialized topics. Oftentimes, a laboratory component of these courses involves practical, hands-on exercises that include, e.g., characterization of magnetic properties of materials and dipoles, measuring the vertical and horizontal component of a magnetic field generated by power supplies, or measuring the EMF induced in a wire coil due to a changing magnetic field. Here, we provide a complement to these activities with a discovery exercise akin to an outdoor magnetic field survey, one that leverages the ready availability of strong small rare earth magnets (“neo-magnets”).

The electrical resistivity of gold was experimentally measured at high pressures from 2 to 5 GPa and temperatures ∼300 K above melting. The resistivity decreased as a function of pressure and incre...

The Earth's core is comprised mainly of Fe and Ni with some light alloying element(s) and the electrical resistivity behavior of these elements is an important property for characterizing geodynamo action, determining energy sources, and for understanding core thermal evolution. Knowledge of the electrical resistivity of solid and liquid transition metals with electronic structures similar to Fe reinforces our understanding of core properties. The electrical resistivity of high purity Co has been measured at pressures up to 5 GPa in a large volume press and at temperatures up to 100 K above the melting temperature. The results demonstrate that resistivity of Co is invariant along the melting boundary. This is interpreted in terms of the antagonistic effects of P-induced reduction in the amplitude of lattice vibrations tending to decrease resistivity, and the P-induced shift of the Fermi level closer to the d-resonance which tends to increase resistivity. We calculated the electronic thermal conductivity of Co using the Wiedemann–Franz law and show that it increases with pressure both in the solid and liquid states and decreases with temperature in the solid and increases in the liquid state. The pressure dependences of electrical resistivity and electronic thermal conductivity calculated from equations involving bulk modulus and the Gruneisen parameter are in reasonable agreement with values measured in this study. The constant resistivity of Co along its melting boundary found in our study portends similar behavior for its electronic structural analog, Fe. This prediction suggests that the electronic thermal conductivity of Fe at Earth's inner core boundary could be similar to its 1 atm value at the melting point. Using this value of thermal conductivity for the inner core boundary would admit thermal convection as an energy source for the geodynamo prior to the birth of the inner core.

Characterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3–9 GPa using a 3000-ton multi-anvil large volume press. A 4-wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry, and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann-Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P-dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behaviour are examined qualitatively through the impact of P-independent local short range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki-Woods ratio and the group of late transition metals with unfilled d-electron band displaying anomalously shallow melting curves, suggest that on the melting boundary, Fe may exhibit the same resistivity behaviour as Ni. This could have important implications for the heat flow in the Earth's core.

We measured the electrical resistivity of high purity Zn along the melting boundary, up to 5 GPa in a large volume press. The electrical resistivity remained constant on the melting boundary, as predicted in a thermodynamics-based model for simple metals. The effects of pressure and temperature on the electrical resistivity of the solid and liquid states are interpreted in terms of their antagonistic effects on the electronic structure of Zn. Within the error of measurements, our melting temperature data agree well with those of the previous studies. The electronic thermal conductivity was calculated from resistivity data using the Wiedemann–Franz law and shows a decrease with temperature in the solid state and an increase in the liquid state, with a large decrease on melting. Comparison of calculated electronic and measured total thermal conductivities indicates that the electronic component dominates over the phonon component in Zn.

O 1s X-ray Photoelectron Spectroscopic (XPS) results for K-silicate glasses near the K-disilicate composition indicate the presence of at least two, and likely three, types of Bridging Oxygen (BO), which are distinguished by the number of K ions coordinated to BO (BO-K moieites). The relative abundances of these moieties cannot be accurately determined from XPS spectra, but based on crystalline K-disilicate, they are likely to be BO, BO-K 1 and BO-K 2 or BO-K 1 , BO-K 2 and BO-K 3 (subscript indicates the number of K + coordinated to BO). The presence of three BO moieties is consistent with crystallographic results for crystalline K-disilicate (K 2 Si 2 SiO 5 ) and their presence in K-silicate glass may be assessed using high quality molecular dynamics studies. The binding energy (BE) separating each BO-K peak is ~ 40 to ~ 70 kJ and sufficient to affect stretching frequencies in Raman and IR spectra, and to effect the electronic properties of O and Si atoms in 17 O and 29 Si NMR spectra. The BO moieties may give rise to separate signals or they may coalesce to produce a broad, asymmetric band in Raman, 29 Si NMR and 17 O NMR spectra, just as they do in O 1s XPS spectra. The O 1s XPS and previously published 17 O NMR spectra of glasses containing ~ 20 and ~ 35 mol% K 2 O are well resolved. Both types of spectra yield the same NBO and BO abundances within experimental uncertainty. For 20 mol% K 2 O glass, the O 1s XPS results yield ~ 21.5 mol% NBO and ~ 78.5% BO whereas the 17 O MAS NMR results are ~ 22.2% NBO and 77.8% BO. The 35 mol% K 2 O glass yields similarly close agreement between O 1s XPS and 17 O MAS NMR spectral fits. Both techniques can provide accurate oxygen species abundances provided the spectra are of high resolution, and provided complete fits are performed on the spectra. A 2D 29 Si MAF NMR spectrum of K-disilicate glass indicates that two Q 4 contributions are present in the spectrum, as previously observed in highly siliceous K-silicate glasses. One explanation for two peaks is that one Q 4 signal represents Q 4 tetrahedra attached to Q 3 tetrahedra and the second peak represents Q 4 attached to other Q 4 species. An alternative explanation is offered based on these findings. The two Q 4 signals may result from different types of BO-K moieties bonded to Si centers of Q 4 species. K + , located in the second coordination sphere of BO, modifies the electronic (valence band) properties of the BO and Si atoms of the tetrahedron, thereby producing two Q 4 signals. The 2D 29 Si MAF NMR, 17 O NMR and O 1s XPS spectra indicate ~ 2 (± 1) mol% O 2 − in the K-disilicate glass. These three types of spectra yield remarkably similar results when high resolution spectra are collected and complete fitting of the spectra are performed.

The Wiedemann-Franz Law is often used to calculate the thermal conductivity of Fe from experimental measurements of the electrical conductivity. It is shown by measurements of the Seebeck coefficient (S) of solid and liquid Fe at pressures up to 6 GPa and temperatures up to 2100 K that the Sommerfeld value ( L 0 = 2.445 × 10 −8 W Ω K −2 ) of the Lorenz number ( L ) represents more than 99% of the electronic component of the thermal conductivity of Fe. Using experimental values of electrical resistivity and thermal conductivity of Fe, L / L 0 is shown to vary by as much as 1.22 in the solid state and 1.32 in the liquid state, signifying a non-negligible phonon component. An expression for the pressure dependence of L at the melting boundary up to 5 GPa is derived for electron-phonon scattering. For Fe-Si alloys, L / L 0 varies more than for pure Fe and generally increases with increasing Si and state of disorder. New values for the conductive heat flow in a pure Fe core of Mercury are presented.

The electrical resistivity and thermal conductivity behavior of Fe at core conditions are important for understanding planetary interior thermal evolution as well as characterizing the generation and sustainability of planetary dynamos. We discuss the electrical resistivity and thermal conductivity of Fe, Co, and Ni at the solid&ndash, liquid melting transition using experimental data from previous studies at 1 atm and at high pressures. With increasing pressure, the increasing difference in the change in resistivity of these metals on melting is interpreted as due to decreasing paramagnon-induced electronic scattering contribution to the total electronic scattering. At the melting transition of Fe, we show that the difference in the value of the thermal conductivity on the solid and liquid sides increases with increasing pressure. At a pure Fe inner core boundary of Mercury and Ganymede at ~5 GPa and ~9 GPa, respectively, our analyses suggest that the thermal conductivity of the solid inner core of small terrestrial planetary bodies should be higher than that of the liquid outer core. We found that the thermal conductivity difference on the solid and liquid sides of Mercury&rsquo, s inner core boundary is ~2 W(mK)&minus, 1. This translates into an excess of total adiabatic heat flow of ~0.01&ndash, 0.02 TW on the inner core side, depending on the relative size of inner and outer core. For a pure Fe Ganymede inner core, the difference in thermal conductivity is ~7 W(mK)&minus, 1, corresponding to an excess of total adiabatic heat flow of ~0.02 TW on the inner core side of the boundary. The mismatch in conducted heat across the solid and liquid sides of the inner core boundary in both planetary bodies appears to be insignificant in terms of generating thermal convection in their outer cores to power an internal dynamo suggesting that chemical composition is important.

The effect of the core thermal conductivity on the heat flow along the adiabat is investigated using direct measurements of electrical resistivity of Fe8.5Si at pressures from 5-24 GPa and temperatures above melting. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of electrical resistivity at melting seem to remain constant at 127 μΩ⋅cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury's core-mantle boundary is estimated between 21.8-29.5 mW m−2, considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury's dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core.

At transition zone depths in subduction zones, deep-focus earthquakes (300–690 km depth) are thought to be associated with faulting that arises from phase transformations. In order to test the viability of this mechanism experimentally, an investigation was conducted on fayalite at high pressure, P, and high temperature, T, under deviatoric stress in order to initiate transformational faulting. Experiments were performed in a 3000-ton multi-anvil press using an 18/11 octahedral cell with 6 piezoelectric transducers mounted on the rear side of the anvils to monitor acoustic activity in situ. Acoustic emission (AE) signals were collected at a sampling rate of 40 MHz using a triggered system and a data buffer for capturing full waveforms of AE events. The use of multiple transducers distributed in a micro-seismic array allowed for events to be located within the sample based on the arrival time of signals and non-linear least squares inversion techniques. Uncertainty in location estimates were on the order of ~1 mm. The system was tested by comparing the contrasting mechanical properties of quartz beads and AgCl samples. The multi-anvil apparatus constitutes an inherently noisy environment both acoustically and electrically, therefore methods of noise reduction were developed. Results of AE experiments on Fe2SiO4 under high pressure (3.7–9.2 GPa) and high temperature (673–1273 K) conditions in the spinel stability field showed acoustic events that locate within or within 1σ of the sample in five experiments defined by the P,T envelope P = 3.9–8.4 GPa and T = 748–923 K. Optical and scanning electron microscopy of the recovered specimens displayed conjugated faulting associated with transition from fayalite (olivine structure) to ahrensite (spinel structure) and microstructural analysis revealed microstructural morphology identical to that found in similar faulting experiments on Mg2GeO4. This is the first time an olivine→spinel structured transition in a silicate mineral has demonstrated macroscopic faulting and associated microstructures, as well as acoustic activity, under conditions that nominally promote plastic deformation.

Electrical and thermal transport properties of liquid Fe under high pressure have important implications for the dynamics and thermal evolution of planetary cores and the geodynamo. However, electrical resistivity (ρ) and thermal conductivity (k) of liquid Fe at high pressure still remain contentious properties. To date, only two experimental investigations of ρ of liquid Fe in the pressure region below 7 GPa are reported in literature. Here we report the results of measurements of ρ for solid and liquid Fe (inversely proportional to k through the Wiedemann-Franz law) at pressures from 3 to 12 GPa, using a large multi-anvil press. We show that ρ of liquid Fe decreases as a function of pressure up to the δ-γ-liquid triple point at ~5.2 GPa, and subsequently remains invariant from 6 to 12 GPa, which is consistent with an earlier study on liquid Ni. Our results demonstrate an important effect of solid phase on the structure and properties of liquid Fe. Our values of ρ for solid and liquid Fe are used to calculate k in Mercury’s solid inner core and along the adiabat in the liquid outer cores of Moon, Ganymede, Mercury and Mars. Our robust values of thermal conductivity place the focus on uncertainties in thermal expansion as the cause of variation in values of core conducted heat. Except for Mercury, our adiabatic heat flux values in these terrestrial cores validate the use of similar values used in several previous studies. Our high values of core adiabatic heat flux in Mercury would provide a stabilizing effect on, and lead to an increase in thickness of, the thermally stratified layer at the top of the core.

Oxygen 1s XPS spectra of a Pb-silicate glass containing 76.6 mol% PbO provide the first accurate, direct measurement of free oxide ion (O2−) in these glasses. O2− constitutes 35 (±3) mol% of total oxygen, with NBO and BO constituting, respectively, 52 (±3) and 13 (±3) mol%. All 29Si NMR and O 1s XPS results for Pb-silicate glasses indicate mol% levels of O2− containing more than ~30 mol% PbO. The O2− abundances are consistent with equilibrium thermodynamic considerations where K ~ 12 for the mass action equation involving NBO, BO, and O2−. Raman and 17O NMR spectra of two CaMg-silicate glasses indicate ~10 (±4) mol% O2− in CaMgSiO4 glass and ~18 (±4) mol% O2− in a Ca0.36Mg0.36Si0.28O1.28 glass. Oxygen species abundances are calculated using experimental results from 13 separate 29Si NMR, 17O NMR, and Raman measurements of Mg-, Ca-, and CaMg-silicate glasses. All reveal mol% levels of O2− with ~1 to 2.6 mol% in metasilicate glass and ~5 to 10 mol% in orthosilicate glass. Recent Raman experimental results also indicate O2− in CaMg-silicate glasses at levels ranging from about 1 to 10 mol%. In all there are 23 separate 29Si NMR, 17O NMR, and Raman measurements indicating mol% levels of O2− in alkaline earth silicate glasses. Eight recent MD simulations of Mg, Ca, and CaMg-silicate glasses include 21 separate simulations over a wide compositional range. All indicate mol% levels of O2− in the glasses demonstrating that the MD simulations and experimental results on these systems are in accord. There are two fundamentally important implications of these studies. First, free oxygen (O2−) is an essential constituent of Pb, Mg, Ca, and CaMg binary silicate melts and glasses. It is not an “accidental” product associated with glass or melt defects. It is instead, a thermodynamically important constituent of these binary melts (and glasses). Second, where melts are equilibrated, the mass action equation relating BO, NBO, and O2− must hold across the entire Ca, Mg, CaMg, and Pb binary systems, thereby requiring the activities and mole fractions of all three species to be defined and finite in the melts. Free oxygen, however, may be too low to be detected in highly siliceous glasses using conventional spectroscopic techniques.

Pressure-induced changes in the solid-state structures and transport properties of three oxobenzene-bridged bisdithiazolyl radicals 2 (R = H, F, Ph) over the range 0–15 GPa are described. All three materials experience compression of their π-stacked architecture, be it (i) 1D ABABAB π-stack (R = Ph), (ii) quasi-1D slipped π-stack (R = H), or (iii) 2D brick-wall π-stack (R = F). While R = H undergoes two structural phase transitions, neither of R = F, Ph display any phase change. All three radicals order as spin-canted antiferromagnets, but spin-canted ordering is lost at pressures

The sound velocities of four iron-nickel-silicon liquids (Fe-5 wt %Ni-6 wt %Si, Fe-5 wt %Ni-10 wt %Si, Fe-5 wt %Ni-14 wt %Si, and Fe-5 wt %Ni-20 wt %Si) are measured between 1460 and 1925 K at ambient pressures using ultrasonic interferometry. The results constrain both the dependence on Si content of the bulk modulus of these liquids and the temperature dependence of their elasticity. These elastic data are utilized to assess both relatively low pressure (to 12 GPa) compressional data on Fe-Si liquids and to extrapolate to higher-pressure and higher-temperature conditions. If a single equation of state for Fe-Ni-Si liquids of a given composition applies from low pressure to near core conditions, then our results imply that the isothermal pressure derivative of the bulk modulus of these liquids is high: likely 8 and above at high temperatures. This high value of the pressure derivative of the bulk modulus at low pressures in Fe-Si liquids causes marked stiffening at higher pressures, leading to notable incompressibility and apparent low values of the pressure derivative of the bulk modulus at core conditions. These results reinforce the conclusion that silicon is not a major alloying component of Earth's core.

A large body of work has focused on resistivity saturation in systems where scattering is caused by impurities or by thermal effects. Electrical resistivity saturation is here classified as either static, where impurity scattering causes saturation, or dynamic, where changing external parameters such as temperature or pressure cause saturation. Resistivity measurements up to 5 GPa show pressure-induced resistivity saturation in Fe17wt%Si by the change in sign from positive to negative of the temperature coefficient of resistivity. The pressure dependence of the Curie temperature is 10.2(8) K GPa−1. The Debye temperature is calculated from the Bloch–Gruneisen equation and yields a pressure dependence of 40(9) K GPa−1.

Malfait challenges our XPS results by arguing that the XPS spectroscopic technique cannot be used to determine small amounts of O2– in potassium silicate glasses. Instead, he claims that there is no free oxide (O2–) in potassium silicate glasses based primarily on his 29Si MAS NMR spectroscopic results. In this rebuttal, we demonstrate that O1s XPS and well-resolved 2D 29Si MAF NMR spectral results of potassium disilicate (K2Si2O5) glass are consistent with each other and that both techniques indicate the presence of a few mol% of O2– in the glass. Neither of these techniques, however, supports the interpretation of the 29Si MAS NMR results presented in the comments of Malfait. The major difficulty relates to the low resolution of the 29Si MAS NMR spectra, which does not reveal the Q4 signal beneath a strong Q3 peak in these spectra. The proof is provided by the 2D 29Si MAF NMR spectrum of potassium disilicate glass in which both Q3 and Q4 peaks are revealed; the 2D 29Si MAF NMR results for potassium disilicate glass are far more informative than 29Si MAS NMR spectra. It demonstrates that the potassium disilicate glass (K2Si2O5) contains greater Q4 intensity, is more polymerized than previously considered, and that O2– is present at ∼2 (±1) mol% in the potassic glass. This O2– value confirms our O1s XPS results. Specific points raised by Malfait are rebutted in Appendix A .

A technique for detecting and measuring phase transitions in a multi-anvil apparatus by measuring the change in travel time for a longitudinal sound wave as a function of pressure is reported. The system measures the time for pulsed ultrasonic signals to travel through a high pressure assembly with a sample in the center. Upon phase change from liquid to solid, the travel time shows an abrupt decrease due to the intrinsic increase in velocity in the sample and a reduced delay between the triggering of an amplitude threshold and the arrival of the waveform. As a proof of concept, results are shown for mercury as it undergoes pressure-induced liquid ⇌ solid transitions at room temperature. We propose that this non-destructive technique may be valuable in situations where other in situ probing techniques cannot be readily used to provide information about changes of state and potentially to study transition kinetics at high pressures as well.

There are many lab exercises for upper-level school students and freshman undergraduates to measure the value of the local acceleration due to gravity (g) near Earth's surface. In these exercises, the value of g is usually taken to be constant. The approach is often based on measuring the period of a pendulum that is inversely proportional to the square root of g. Traditional measurements of the period of a simple or inclined pendulum involve use of a stopwatch to measure the time required to complete a number of oscillations, but other more sophisticated measurement techniques for greater accuracy, such as a photogate timing system, measuring the time-dependent tension on the string, or using a stepper motor connected to a conical pendulum have been described. Using video imaging, the mechanics of objects dropped from some height has also been used to determine g. In physics courses where physical principles are applied to Earth problems, however, the goal is usually to measure a change in a potential field, such as Earth's gravitational field, in order to determine anomalous subsurface characteristics. In this paper, we describe an indoor exercise to measure the local change in g resulting from a large anomalous mass near the observation location.

A simple cooling system for a 3000-ton multi-anvil press was developed for temperatures below room temperature at high pressures. It is much simpler in design, easier to make and use, and has the same cooling capability as the previous design. The new system uses a steel ring surrounding the module wedges, which contains liquid nitrogen (LN2) that flows freely through a port to flood the interior of the pressure module. O-rings on the steel ring seal in LN2 while permitting compression. Two different cooling systems reach ∼220 K which suggests that thermal equilibrium for this press is reached between the removal and influx of heat.

The heterocyclic bisdithiazolyl radical 1b (R1 = Me, R2 = F) crystallizes in two phases. The α-phase, space group P2₁/n, contains two radicals in the asymmetric unit, both of which adopt slipped π-stack structures. The β-phase, space group P2₁/c, consists of cross-braced π-stacked arrays of dimers in which the radicals are linked laterally by hypervalent 4-center 6-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility measurements on α-1b indicate Curie-Weiss behavior (with Θ = -14.9 K), while the dimer phase β-1b is diamagnetic, showing no indication of thermal dissociation below 400 K. High-pressure crystallographic measurements indicate that the cross-braced π-stacked arrays of dimers undergo a wine-rack compression, but the dimer remains intact up to 8 GPa (at ambient temperature). The resistance of β-1b to dissociate under pressure, also observed in its conductivity versus pressure profile, is in marked contrast to the behavior of the related dimer β-1a (R1 = Et, R2 = F), which readily dissociates into a pair of radicals at 0.8 GPa. The different response of the two dimers to pressure has been rationalized in terms of differences in their linear compressibilities occasioned by changes in the degree of cross-bracing of the π-stacks. Dissociation of both dimers can be effected by irradiation with visible (λ = 650 nm) light; the transformation has been monitored by optical spectroscopy, magnetic susceptibility measurements, and single crystal X-ray diffraction. The photoinduced radical pairs persist up to temperatures of 150 K (β-1b) and 242 K (β-1a) before reverting to the dimer state. Variable-temperature optical measurements on β-1b and β-1a have afforded Arrhenius activation energies of 8.3 and 19.6 kcal mol(-1), respectively, for the radical-to-dimer reconversion. DFT and CAS-SCF calculations have been used to probe the ground and excited electronic state structures of the dimer and radical pair. The results support the interpretation that the ground-state interconversion of the dimer and radical forms of β-1a and β-1b is symmetry forbidden, while the photochemical transformation is symmetry allowed.

The electrical resistivity of solid-state tungsten (W) and rhenium (Re) was experimentally measured at high pressures up to 5 GPa and temperatures up to ∼2273 K using a four-wire resistivity method. For both metals, the resistivity decreased as a function of pressure and increased as a function of temperature, in excellent agreement with 1 atm data. The Wiedemann–Franz law was used to calculate the total thermal conductivity from the resistivity. Thermal conductivity increased as a function of pressure for both metals, but decreased as a function of temperature for W and increased for Re. Values of thermal conductivity at high pressures and temperatures are consistent with most recommended previous experimental studies at 1 atm.

The heat capacity at constant pressure (CP) data of rutile and synthetic TiO2II were measured in the temperature range of 5–465 K using the heat capacity option of the physical property measurement system (PPMS) and by differential scanning calorimetry (DSC). The entropy values for rutile and TiO2II at standard temperature and pressure conditions calculated from the measured heat capacity data are 50.22 ± 0.20 and 47.50 ± 0.20 J mol−1 K−1, respectively. The CP for both phases were also calculated using the Kieffer model to extrapolate CP to higher temperatures beyond experimental range. These new thermodynamic data were used to calculate the phase transition boundary between rutile and TiO2II with the help of other parameters available in the literature. The calculated phase boundary is compared with previous experimental results and possible reasons for the differences are discussed.

The pressure-induced anomalously high AC conductivity of zeolite NaA mixed with water was measured by impedance spectroscopy at various water/zeolite ratios. The conductivity reaches a maximum value at 0.9–1.4 GPa with increasing water content of up to 20 wt.% in NaA + water. The high ionic conductivity of NaA compressed in water is interpreted to result from cation diffusion in the quasi-liquid Na+–H2O intra-channel system enhanced by the filling of additional H2O sites. The pressure range of anomalously high AC conductivity in NaA enlarges towards higher pressures with decrease of the water/zeolite ratio. An abrupt drop in conductivity observed at P > 1.5 GPa appears to be associated with freezing of intra-channel water. After pressure release, the overhydrated state of the zeolite kept in a closed container can be preserved for a long time, providing abnormally high conductivity which is comparable with that of Na+ β-alumina.

Benzoquino-bis-1,2,3-dithiazole 5 is a closed shell, antiaromatic 16π-electron zwitterion with a small HOMO-LUMO gap. Its crystal structure consists of planar ribbon-like molecular arrays packed into offset layers to generate a "brick-wall" motif with strong 2D interlayer electronic interactions. The spread of the valence and conduction bands, coupled with the narrow HOMO-LUMO gap, affords a small band gap semiconductor with σRT = 1 × 10-3 S cm-1 and Eact = 0.14 eV for transport within the brick-wall arrays. Closure of the band gap to form an all-organic molecular metal with σRT > 101 S cm-1 can be achieved by the application of pressure to 8 GPa.

A critical feature of the electronic structure of oxobenzene-bridged bisdithiazolyl radicals 2 is the presence of a low-lying LUMO which, in the solid state, improves charge transport by providing additional degrees of freedom for electron transfer. The magnitude of this multiorbital effect can be fine-tuned by variations in the π-electron releasing/accepting nature of the basal ligand. Here we demonstrate that incorporation of a nitro group significantly stabilizes the LUMO, and hence lowers Ueff, the effective Coulombic barrier to charge transfer. The effect is echoed, at the molecular level, in the observed trend in Ecell, the electrochemical cell potential for 2 with R = F, H and NO2. The crystal structures of the MeCN and EtCN solvates of 2 with R = NO2 have been determined. In the EtCN solvate the radicals are dimerized, but in the MeCN solvate the radicals form superimposed and evenly spaced π-stacked arrays. This highly 1D material displays Pauli-like temperature independent paramagnetic behavior,...

A new custom-designed system for a 3000 ton multi-anvil press has been developed to reach temperatures below room temperature at high pressures. The system was designed to remove heat selectively and conductively from the sample volume through six of the eight tungsten carbide (WC) cubes in direct contact with the octahedral pressure cell. The key components of the system include Cu cooling fins sandwiched between neighboring cube faces and the connected Cu heat exchange chamber through which liquid nitrogen flows. Currently, this system enables us to reach temperatures down to 220 K at pressures up to 8 GPa, but it can be easily modified to retain similar cooling capability at the highest pressure the press can reach (ca. 25 GPa).