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Densification in glassy networks has traditionally been described in terms of short-range structures, such as how atoms are coordinated and how the coordination polyhedron is linked in the second coordination environment. While changes in medium-range structures beyond the second coordination shells may play an important role, experimental verification of the densification beyond short-range structures is among the remaining challenges in the physical sciences. Here, a correlation NMR experiment for prototypical borate glasses under compression up to 9 GPa offers insights into the pressure-induced evolution of proximity among cations on a medium-range scale. Whereas amorphous networks at ambient pressure may favor the formation of medium-range clusters consisting primarily of similar coordination species, such segregation between distinct coordination environments tends to decrease with increasing pressure, promoting a more homogeneous distribution of dissimilar structural units. Together with an increase in the average coordination number, densification of glass accompanies a preferential rearrangement toward a random distribution, which may increase the configurational entropy. The results highlight the direct link between the pressure-induced increase in medium-range disorder and the densification of glasses under extreme compression.

Among amniotes, turtles are the only clade that lay aragonitic eggs. Because aragonite is a metastable mineral, unequivocal preservation of aragonite in fossil turtle eggs has only been reported from Pliocene deposits. Here, we report in situ preservation of aragonite in a turtle egg from the Judith River Formation (Campanian) of Montana, USA. We utilized electron backscatter diffraction (EBSD) and Raman spectroscopy to explore the carbonate mineral polymorphs in the eggshell. The EBSD maps show the presence of both aragonite and calcite with the former preserved as needle-like crystal, a feature of all turtle eggshells. The presence of aragonite is independently validated by Raman maps. This dual approach provides direct, unambiguous evidence that the record of aragonitic turtle eggshell dates back at least to the Campanian (ca. 76 Ma) and supports the hypothesis that aragonitic eggshell is a synapomorphy of all turtles. The presence of pristine aragonite also indicates minimal taphonomic alteration at the fossil locality. Consequently, diverse invertebrate or vertebrate fossils from localities with aragonitic turtle eggs may provide high quality, unaltered palaeoenvironmental information.

Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation., Ion migration can induce overshoot of luminance in normal 3D perovskite light-emitting diode devices and results in reduced lifetime. Here Kim et al. show that the ion migration and overshoot can be suppressed in 3D/2D hybrid perovskites, leading to 21 times longer operational lifetime.

Raman spectroscopic analyses of thermally altered organic materials can be used to assess the paleothermometry of the sedimentary deposits. Although this technique has been widely applied to diverse microfossils, macroscopic vertebrate fossils have been neglected. In this paper, we show that fossil eggshells can be used for this purpose by demonstrating the paleothermometric potential of diverse amniotic eggshells from the Wido Volcanics (Upper Cretaceous, South Korea) that contain thermally altered organic material. We estimate the maximum paleotemperature recorded in the eggshells using Raman spectroscopic data and the spectrum deconvolution technique, which was invented and developed by organic geochemists. The results show that the same type of eggshells record different paleotemperature gradients depending on their spatial distribution in the fossil locality, whereas different types of eggshells from similar locations show similar paleotemperature gradients (except for one specimen with a peculiar microstructure). These findings are further supported by Fourier transform infrared spectroscopic results, which focus on thermally altered organic materials, and electron backscatter diffraction data, which focus on calcite twinning. This study suggests that fossil eggshells are useful and reliable materials for paleothermometry because thermally altered organic materials and calcites of eggshells provide independent opportunities to assess paleothermometry. We propose that fossil eggshells may be useful for evaluating the thermal evolution of sedimentary basins.

NH4H2AsO4 (ADA) is a model compound for understanding the mechanism of phase transitions in the KH2PO4 (KDP) family of ferroelectrics. ADA exhibits a paraelectric (PE) to antiferroelectric (AFE) phase transition at TN ∼ 216 K whose mechanism remains unclear. With the view of probing the role of the various protons in the transition mechanism, we have employed the high-resolution technique of magic angle spinning at the high Zeeman field of 21.1 T (1H resonance at 900 MHz). We measured the temperature dependence of the isotropic chemical shift and spin–lattice relaxation time, T1, of the O–H···O and NH4+ protons through the TN. As T → TN, NMR peaks from the PE and AFE phases are seen to coexist over a temperature range of about 3 K, showing formation of nearly static (lifetime > milliseconds) pretransitional clusters in this lattice as it approaches its TN, consistent with the near first-order nature of the phase transition. The isotropic chemical shift of the O–H···O protons exhibited a steplike anomaly a...

Variable temperature magic angle spinning (MAS) NMR measurements are reported on

Dimethylammonium zinc formate ([(CH3)2NH2]Zn(HCOO)3 or DMZnF) is a model system for the study of hybrid perovskite-like dielectrics. It undergoes a phase transition from the paraelectric to ferroelectric phase at ∼166 K, as observed via NMR spectra. The mechanism of this phase transition has been shown to have contributions from ordering of the hydrogen bonds between [(CH3)2NH2]+ (DMA+) and the formate groups as well as buckling of the metal-formate framework, but the transition dynamics and atomistic mechanism are not fully clear. This work presents dielectric constant measurements as evidence of cluster formation of the low-temperature phase and the relaxor-like behavior of this metal–organic framework above the phase transition temperature. 13C CP-MAS is used to track the evolution of the chemical shift, T1, and T2 of the dimethylammonium cation and formate groups from room temperature to 120 K. 2D 13C–13C correlation measurements provide evidence of the formation of pretransitional clusters above the ...

LiH2PO4 (LDP) is a favored candidate for hydrogen fuel cells, but the mechanism of its high protonic conductivity remains unclear. A complicating factor has been the lack of resolution in the repor...

We have studied the charge transport and dielectric properties of KH2PO4 (KDP) single crystals, irradiated by proton beams with high energies up to 20 MeV, by means of the temperature-dependent electrical conductivity and dielectric constant measurements. It is shown that the electrical conductivity and the electric dipole moment may be sensitively controlled by the proton irradiation energy and dose. The activation energy and the dipole moment were shown to be strongly correlated.

Plasma-facing components (PFCs) in fusion devices are exposed to an irradiation environment of high particle flux. Among various candidate materials for PFCs, graphite is used as a first-wall material of the Korea Superconducting Tokamak Advanced Research (KSTAR) and tungsten is being strongly considered as a divertor material of the international thermonuclear experimental reactor (ITER). In this experiment, graphite and tungsten targets were irradiated by using low-energy helium ions, and the irradiation’s influence on each target was studied with particular emphasis on the surface change. Changes in the surface morphology were observed by using scanning electron microscopy (SEM); induced disorders in the structure were investigated by using X-ray diffraction (XRD), Raman spectroscopy, and electron spin resonance (ESR) measurements.

Single crystals of LiH2PO4 were grown from an aqueous solution by slow evaporation method, the morphology being observed by optical and scanning electron microscopes and the crystal structure being labeled by powder X-ray diffraction. The virtual crystal was simulated in accord with the realistic crystal observed, with the following faces in the space group P n a 2 1 − C 2 v 9 : pyramid {111}, { 11 1 ¯ } ; prism {110}; dome {011}, { 01 1 ¯ } , { 20 1 ¯ } ; pedion { 00 1 ¯ } . From comparison of the macroscopic morphology and the microscopic crystal structure, terminating groups of the top layer surfaces are suggested.

Phase transformations in squaric acid (H 2 C 4 O 4 ) have been investigated by thermogravimetry and differential scanning calorimetry with different heating rates β . The mass loss in TG apparently begins at onset temperatures T di =245±5 °C ( β =5 °C min −1 ), 262±5 °C ( β =10 °C min −1 ), and 275±5 °C ( β =20 °C min −1 ). A polymorphic phase transition was recognized as a weak endothermic peak in DSC around 101 °C ( T c + ). Further heating with β =10 °C min −1 in DSC revealed deviation of the baseline around 310 °C ( T i ), and a large unusual exothermic peak around 355 °C ( T p ), which are interpreted as an onset and a peak temperature of thermal decomposition, respectively. The activation energy of the thermal decomposition was obtained by employing relevant models. Thermal decomposition was recognized as a carbonization process, resulting in amorphous carbon.

The proton and phosphorus dynamics of the superprotonic conduction in the LiH2PO4 system has been studied by means of 1H and 31P NMR rotating-frame nuclear magnetic resonance (NMR). The temperature-dependent 1H NMR rotating-frame spin–lattice relaxation time measurements revealed in a sensitive manner the evolution of the microscopic environment and proton dynamics of the two distinct hydrogen-bond types in the system, which is quite compatible with the electrical conductivity and the impedance spectroscopy measurements. Besides, the proton dynamics was found to be coupled to the reorientational motion of the PO4 tetrahedra.

Plasma-facing materials in fusion devices are irradiated by a high particle flux from a dense plasma. Graphite tiles, widely used as plasma-facing materials, were irradiated with a helium plasma of a high flux and low energy; the damage in the graphite-tile target was investigated. Changes in the surface morphology were observed from scanning electron microscopy; the electrical conductivity was decreased from four-probe measurement; the intensity of the graphite disorder peak was increased from Raman spectroscopy.

We have carried out Raman, electron spin resonance (ESR), and X-ray photoemission (XPS) spectroscopy measurements on the graphite tiles modified by electron and proton irradiation. While increase in local order was observed in the electron-irradiated sample, structural disorder and amorphization were revealed in the proton-irradiated sample, with much reduced electrical conductivity. Besides, a narrow ESR peak attributed to localized spins, closely associated with C–OH bonds as identified by the XPS measurements, was detected in the proton-irradiated sample.

Variable temperature magic angle spinning (MAS) NMR measurements are reported on 1H and 31P nuclei in KH2PO4 (KDP) in the vicinity of its paraelectric-ferroelectric phase transition temperature, T c, of 123 K, to examine the transition mechanism, in particular if this is a model order-disorder type or whether it also involves a displacive component. It has been well established that the temperature variation of the isotropic chemical shift, δ iso, in NMR measurements of the nuclei directly involved in the transition should remain constant or change smoothly through T c for an order-disorder type transition but it should show an anomalous change for a displacive one. Here we demonstrate that the δ iso for both 31P and 1H nuclei in KDP show clear anomalies as a function of temperature around KDP's T c, providing direct evidence of a displacive component for the phase transition of KDP in contrast to the generally accepted notion that it is a model order-disorder type.

The electrical properties of single-walled carbon nanotubes (SWNTs)/TlH2PO4 composites have been studied, a metallic transition being observed around a SWNTs concentration of 0.2 wt.% and investigated by means of impedance spectroscopy. This work represents the first study of its kind to show that nanoparticles may be employed as valued additives that are compatible with the solid acids, providing for increased electrical conductivity of fuel-cell electrolytes. A two orders of magnitude increase in the surface capacitance was observed in the composite, opening up a possibility of new solid acid electrolytes for fuel cells and composite electrolytes serving as a supercapacitor by itself.

The proton conductivity of KH2PO4 (KDP) was modi ed by means of proton irradiation. Our neutron di raction and high-resolution 1H nuclear magnetic resonance measurements indicate that modi cation in the O O bond length in the KDP system induced by the proton-beam treatment is responsible for the change in the proton conduction, which is accompanied by a reduction in the proton-hopping activation energy.

Protonic currents play a vital role in electrical signalling in living systems. It has been suggested that succinoglycan plays a specific role in alfalfa root nodule development, presumably acting as the signaling molecules. In this regard, charge transport and proton dynamics in the biopolymer exopolysaccharide succinoglycan have been studied by means of electrical measurements and nuclear magnetic resonance (NMR) spectroscopy. In particular, a dielectric dispersion in the system has revealed that the electrical conduction is protonic rather electronic. Besides, our laboratory- and rotating-frame 1H NMR measurements have elucidated the nature of the protonic conduction, activation of the protonic motion being associated with a glass transition.

We have carried out an impedance spectroscopy study on a series of proton-irradiated KH2PO4 (KDP) systems. A systematic modification was observed in the transverse dipole moment of the proton-irradiated KDP systems, associated with hydrogen-ion displacements, as obtained from dielectric constant measurements by using a mean-field approximation. Besides, intercorrelation of the charge transport with the dielectric properties was revealed, both having closely to do with the hydrogen-bond modification.

Our systematic study employing high-resolution nuclear magnetic resonance measurements shows that the hydrogen bonds and proton transport in the KH2PO4 (KDP) system may be tuned sensitively by proton irradiation. In particular, the hydrogen-bond length in KDP increased by a properly chosen dose of proton irradiation is shown to give rise to a minimum in the activation energy of proton hopping in the hydrogen-bond direction.

Superprotonic conduction in the LiH2PO4 system has been studied by means of high-resolution nuclear magnetic resonance measurements, which enabled us to distinguish dynamics of the two different hydrogen bonds in the structure. The protonic motion, primarily associated with the longer hydrogen bond, rather than the Li ionic motion, was revealed to dictate the extraordinarily high electrical conductivity of the system.

We have studied the metal–insulator transition (MIT) taking place at 340 K in vanadium dioxide nanoparticles. A peculiar nanosize effect on the 10-nm-sized VO2 nanoparticles is reported. While the infrared transmittance at high wave numbers displayed a broad transition behavior, the magnetic susceptibility and infrared transmittance at low wave numbers showed a sharp first-order MIT. Our results suggest that the size effect on the MIT is due to the surface region while the core region undergoes the same MIT as that in the bulk.

Electron spin resonance measurements of proton-irradiated graphite have revealed detailed nature of proton-irradiation-induced defects. Our results indicate that proton-irradiation creates confined defect regions of a metallic island surrounded by an insulating magnetic region which “isolates” the metallic island inside from the metallic graphite background outside. We have thus come up with a picture of phase separation in proton-irradiated graphite comprising three regions of distinct electrical and magnetic properties.

Microscopic environments and dynamics in LiCoO2 systems were probed by L7i nuclear magnetic relaxation measurements with regard to the structural defects as revealed by x-ray diffraction and electron spin resonance measurements. Thus, the structural defects of differing degrees, associated with Li vacancies, were well accounted for in the temperature-dependent spin-lattice relaxation rate analysis, and in the structural and dynamical inhomogeneity as derived from the relaxation patterns.

The ferroelectric phase transition temperature was significantly raised by 5K in partially deuterated KH2PO4 irradiated by a proton beam. Increase in the hydrogen bond length was indicated by the dielectric constant analysis. Deuteron nuclear magnetic resonance (NMR) measurements of the electric field gradient tensor showed atomic displacement after the proton irradiation, and P31 NMR measurements of the chemical shift tensor revealed phosphorous displacement in the hydrogen-bonded direction and the PO4 tetrahedral distortion. Increase of the phase transition temperature can be closely related to the structural modification involving the hydrogen-bond geometry.