The V-Nb-Mo-Ta-W refractory high-entropy alloy exhibits high hardness and can maintain its strength at high temperatures. However, it would be advantageous to enhance the hardness of this alloy. This could be accomplished by shock-compression processing based on severe deformation caused by a projectile impact. The present work examines the effects of shock compression at pressures up to 31 GPa. X-ray diffraction analyses of shocked samples revealed no change in the crystal structure, but reduced crystallite sizes, and the appearance of strain and defects. Mapping of constituent elements using energy-dispersive spectroscopy confirmed that the composition was V17Nb22Mo21Ta21W19 and although elemental segregation occurred in some regions within the shocked samples, the grain and grain boundary microstructures apparent in the as-cast alloy were less obvious. The Vickers hardness of samples shocked at 8, 17, 23, and 31 GPa was 655 f 77, 708 f 53, 834 f 64, and 750 f 36 HV, respectively, whereas that of the unshocked material was 611 f 30 HV. These increases in hardness are slightly greater than those obtainable using other processing methods.

Phase transitions of the ionic liquid (IL) with a bulky cation were investigated at low temperature (LT) and high pressure (HP). The IL studied was trihexyl(tetradecyl)phosphonium hexafluorophosphate, [P666,14][PF6]. Upon cooling of 4.6 K/min, LT alpha phase was formed at 286 K. In the unit cell, void space was visualized. LT crystallization was influenced slightly by the cooling rate. Under HP, the crystal (alpha-phase) transformed into a flexible crystal ((3 phase) at 0.7 GPa by reducing void space. The HP alpha-(3 phase transition of [P666,14][PF6] was caused by compression of the void space within the unit cell. During the (3 phase with drastic volume contraction, the void fraction was almost constant. At 4.1 GPa, the flexible (3 phase transformed to a rigid ionic liquid crystal. Even at the maximum pressure of 7.2 GPa, a reversible volumetric phase transition was observed in the bulky [P666,14] [PF6].

Cobalt spinel ferrites are an important class of materials with inverse spinel structures in which Co2+ ions occupy octahedral sites. These materials can exhibit high coercivity and thus can have various uses in applications involving magnetism. The magnetic properties of these ferrites are also affected by variations in strain and crystallite size. Among the techniques developed to prepare nanosized particles of such compounds, mechanical alloying (MA) was adopted in this study to fabricate nanosized cobalt spinel ferrites (CoFe2O4 and Co1.5Fe1.5O4) with high strain. In addition, specimens were subjected to severe plastic deformation based on shock compression via a projectile impact method, generating pressures as high as 30 GPa, to produce a wide range of strains and crystallite sizes. The X-ray diffraction patterns were identified to a spinel structure irrespective of shock pressure. In the Co1.5Fe1.5O4 and CoFe2O4 samples shocked at 30 GPa, decomposition to cobalt oxide and creation of byproducts were found, respectively; however, no other specimens exhibited phase transitions or the formation of additional byproducts. Raman spectra also suggested a metastable cation distribution between tetrahedral and octahedral sites as a result of the MA process. The strain and crystallite size did not vary monotonically with the shock pressure, nor did the magnetic properties exhibit linear correlations with strain and crystallite size. The trend in the magnetic properties cannot be evaluated on the sole basis of strain or crystallite size. Shock compression can be regarded as a novel processing technique capable of broadly controlling magnetic properties without compromising crystal structure or composition of various nanomagnetic materials.

The complex phase behaviors of ionic liquids near the multiphase coexistence point (MCP) were examined using synchrotron small- and wide-angle x-ray scattering. The cations utilized in this study were 1-alkyl-3-methylimidazolium [Cnmim]+, where n represents the alkyl chain length, and the anions were Cl-, Br-, I-, and [NO3]-. In proximity to the alkyl chain length corresponding to the MCP (nMCP), crystal polymorphism or multiple phase transition pathways were induced under low-temperature (LT) or high-pressure (HP) conditions. Within the [C8mim][X] series, [C8mim]Cl and [C8mim]Br were crystallized under HP conditions. The multiphase coexistence in [C10mim]Br and [C10mim][NO3] was sensitively dependent on the heating rate and was explained by the generalized Gibbs phase rule. With increasing deviation from nMCP, the LT and HP phase behaviors of [Cnmim][X] considerably changed.

Synchrotron small- and wide-angle X-ray scattering and Raman spectroscopy were used to investigate the high-pressure (HP) liquid-liquid transitions (LLTs) in quaternary ammonium and phosphonium ionic liquids (ILs) at room temperature. Bis(trifluoromethylsulfonyl)imide ([TFSI]-) was used as the anion, and triethyloctylammonium, (2-ethoxyethoxy)ethyltriethylammonium ([N222(2O2O2)]+), triethyloctylphosphonium, and (2-ethoxyethoxy)ethyltriethylphosphonium ([P222(2O2O2)]+) were used as cations. In diether-substituted [N222(2O2O2)][TFSI] and [P222(2O2O2)][TFSI], the polar/nonpolar nanodomains were not formed due to the flexible and curled alkyl chains. Despite no nanodomain, HP LLT occurred with changing the local structures. A series of quaternary ammonium and phosphonium ILs exhibited entirely different HP behavior, which implies that the ether bonds of the cations have an intrinsic property.

The phase varieties of ionic liquids (ILs) were examined at low temperature (LT) and high pressure (HP) using small-and wide-angle X-ray scattering. The cations of these ILs were 1-alkyl-3-methylimidazolium ([Cnmim]+), and the anion was iodide (I-). [C10mim]I was located in the vicinity of the multiphase coexistence point on the phase diagram, and the complicated phase behavior was induced at LT. [C12mim]I indicated a simple and reversible phase transition at LT. The LT crystal structure of [C12mim]I was characterized by the 00 & ell; Bragg reflections, derived from the stacking layers. Under HP, a double peak at low Q appeared in [C12mim]I with the loss of stacking layers. The crystal flexibility of the ILs under HP was estimated using the second-order Birch-Murnaghan equation.

Lightweight medium entropy alloys (LMEAs) of AlxTiVCr (x = 1, 1.5, 2, 2.2, 2.4, 2.5, 3, or 4) were prepared, and shock compression was conducted to enhance their mechanical properties. The Vickers hardness value of 704 HV for as-cast Al2.2TiVCr alloy is highest among the prepared alloys and it compares favorably with other LMEAs. In all shocked samples, no phase transition was observed except for x = 2.5, whereas broadening of the Bragg peaks was observed. For AlxTiVCr alloy with dual-phase structure, large cracks were observed, and some cracks propagate inside FCC phase grains, changing propagation direction when encountering BCC grain. The Vickers hardness was enhanced by shock compression in some conditions. Especially, the specimen having an x value of 4 exhibited a 43% increase in hardness after shock compression at 30 GPa. This study offers important insights into hardening the alloys by shock compression.

The luminescence properties of single-component and binary ionic liquids (ILs) were investigated in relation to their nanoheterogeneities. The cations of the ILs were 1-alkyl-3-methylimidazolium and trihexyl(tetradecyl)phosphonium ([P666,14]+). The anions were [Cl]-, [Br]-, [MnCl4]2-, and [MnBr4]2-. Even in the liquid state, the binary mixtures of η[P666,14][Br] + [P666,14]2[MnBr4] (η = 0.5, 1, 2, and 4) emitted green light at room temperature. In the mixed liquids, the prepeak derived from the nanoheterogeneity was observed at a low Q position on the small- and wide-angle X-ray scattering patterns. With increasing temperature, the luminescent intensities of the IL mixtures increased, contrary to the almost constant prepeak intensity. The luminescence intensity maximum of the mixture (η = 0.5) was observed at 403 K.

In this study, two novel quadruple perovskite compounds SmA ' 3Co4O12 (A ' = Cu, Mn) were synthesized using a high-pressure synthesis method. Structural analysis of the perovskites using synchrotron X-ray powder diffraction revealed that both SmCu3Co4O12 and SmMn3Co4O12 have cubic Im 3 structure. In the temperature range of 2-300 K, SmCu3Co4O12 did not exhibit a magnetic phase transition, whereas SmMn3Co4O12 exhibited a paramagnetic to ferrimagnetic phase transition at similar to 90 K. A comparison of structural information, X-ray absorption near edge structure, and magnetic properties revealed that the low-spin state (S = 0) characterizes the spin state of Co3+ when the A ' site is occupied by Cu3+. However, when the A ' site is occupied by Mn3+, the Co3+ spin state is in a high-spin state (S = 2), indicating that a long-range magnetic phase transition occurs owing to the magnetic interaction between the Mn and Co ions.

Complicated phase transitions were observed in a single-component 1-decyl-3-methylimidazolium nitrate ([C10mim][NO3]) ionic liquid (IL) using Raman spectroscopy and synchrotron small- and wide-angle X-ray scattering (SWAXS). Time-resolved synchrotron SWAXS could distinguish the phase transitions depending upon the cooling rate. Low-Q peaks representing a few kinds of layered structures were decomposed. Multiphase coexistence was observed in [C10mim][NO3] at specific cooling rates (8-9 K/min). Ionic liquid crystals (ILCs), hybrid-layered crystals, and hexagonal close-packed structures coexisted simultaneously. At the cooling rate region, the reentrant phase transition of the ILC phase upon heating was observed.

The phase behavior of an ionic liquid (IL) was investigated at low temperature (LT) and high pressure (HP). The utilized IL was 1-decyl-3-methylimidazolium bromide ([C10mim][Br]), whose cation possesses a long alkyl side-chain. The LT- and HP-crystal polymorphs of [C10mim][Br] were observed conducting small- and wide-angle X-ray scattering (SWAXS) experiments. Upon cooling, a liquid crystal was formed, which subsequently transformed into crystalline species with the modulated layered structure possessing the double Bragg reflection. In addition to the layered structure, the hybrid layered structure coexisted upon heating. At HP, 00ℓ Bragg reflections representing the layered structure were not observed in SWAXS patterns. The HP-crystal phase of [C10mim][Br] was characterized by double Bragg reflection in the low scattering wavevector region. The non-layered HP-crystal caused the large bulk modulus.

The hydrogen/deuterium (H/D) exchange of ionic liquid (IL) occurred in the deuterated solutions. Kinetic H/D exchange was investigated via Raman spectroscopy and pH measurements. The ILs employed were amphiphilic 1-alkyl-3-methylimidazolium triflate ([Cnmim][OTf] (n = 2, 4, 6, and 8)) and hydrophilic [C2mim][X] (X = Cl, Br, I, and BF4). The H/D exchange occurred in the [C2mim][OTf]-deuterated methanol (MeOD-d4) solutions and was dependent on the additive concentration. For [C2mim][X]-D2O (X = Cl, Br, and I), which did not possess nano-heterogeneity and the anionic anisotropic shape factor, significant relationships were observed among the H/D exchange rate, pD, and ion-pairing strength.

Molybdenum(VI) oxide (MoO3) is a promising semiconductor material that can be used in several functional applications. Understanding the structural response of MoO3 under high-pressure and high-temperature conditions is important for designing a material used in device applications. An X-ray free electron laser (XFEL) enables the structural response under extreme conditions to be probed at the nanosecond timescale. We describe laser-driven shock compression experiments on MoO3 using an XFEL to directly observe the structural evolution of MoO3. When a laser-driven shock wave arrives at a pressure of 61 GPa, MoO3 melts immediately and remains in the molten state for a few nanoseconds. Rapid recrystallization to the α-MoO3 phase and a high-pressure phase MoO3-II is also observed on nanosecond timescales during pressure release. Our results provide insights into the kinetic and phase transition under shock compression and represent the advancement toward the understanding structural response of MoO3 under high-pressure, high-temperature conditions, which has not been studied.

The hydrogen bonding of nanoconfined water (water pockets) and ionic liquid crystals (ILCs) was examined in a hydrophilic IL-D 2 O system by Raman spectroscopy. The IL was 1-decyl-3-methylimidazolium nitrate ([C 10 mim] [NO 3 ]). The lyotropic ILC of [C 10 mim][NO 3 ]-70-90 mol% D 2 O was obtained at room temperature. The hydrogen bonding states of the water pocket and lyotropic ILC phases were represented by additional nearly -free and very strong hydrogen bondings. H/D exchange occurred at room temperature in [C 10 mim][NO 3 ]-D 2 O, promoted by the gel -inherent hydrogen bonding of water.

Ionic liquids, specifically 1-alkyl-3-methylimidazolium nitrate, [Cnmim][NO3] (n = 4, 6, and 8), underwent pressure-induced amorphization. High-pressure-driven multiple-glass transitions were clarified through Raman spectroscopy. Both double- and triple-glass transitions were observed in [Cnmim][NO3]. Small- and wide-angle X-ray scattering revealed a prepeak representing nanoheterogeneity in [Cnmim][NO3] (n = 6 and 8) at ambient pressure. Despite the decrease in intensity at glass transition pressure, the prepeak of [C8mim][NO3] still existed. In [C8mim][NO3], the first glass-glass transition occurred a nanoheterogeneous double glass. The second glass-glass transition marked the transition from a heterogeneous to a homogeneous glass.

The shock-compression method enables dense solidification at relatively low temperatures, and fabrication of bulk material is possible without thermal alteration of the nonequilibrium phases. A metastable phase of an equiatomic Al-Ti-V-Cr-Si high-entropy alloy was prepared by mechanical alloying, and the obtained alloy was solidified by shock-compression to retain the metastable phase of AlTiVCrSi. The bulk form composed of a metastable body-centered cubic (BCC) solid solution was attained after shock solidification at a pressure of 11 GPa. However, when shock stresses of 21 GPa and 31 GPa were applied, the intermetallic compounds (Ti, V)5Si3 and Al8(V, Cr)5 were formed in addition to the BCC phase. The formation of these intermetallic compounds during shock compression was consistent with thermodynamical predictions and empirical parameters for phase prediction. The bulk AlTiVCrSi samples shock-solidified at 11 GPa and 21 GPa exhibited Vickers hardness values greater than 1000 HV, whereas that for the sample shock-solidified at 31 GPa was 400 HV. The decrease in hardness was attributed mainly to the formation of a large number of cracks.

The phase transitions of a fluorinated ionic liquid (fIL) were examined at low temperature (LT) by X-ray diffraction and Raman spectroscopy. The fIL was 1-ethyl-3-methylimidazolium perfluorobutanesulfonate ([C2mim][PFBS]). The cation and anion possessed conformational degrees of freedom. The trans and gauche conformers of [PFBS]- coexisted in the liquid state. The LT crystal polymorph of the [C2mim][PFBS] was observed, and [C2mim][PFBS] possessed the large unit cells. The gauche' conformer of [PFBS]- appeared, accompanying with the phase transition at 220 K.