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phase diagram and structural transformations of molten P
O
under pressureBrazhkin, V. V.*; Katayama, Yoshinori; Lyapin, A. G.*; Saito, Hiroyuki
Physical Review B, 89(10), p.104203_1 - 104203_4, 2014/03
Times Cited Count：9 Percentile：38.87(Materials Science, Multidisciplinary)The PO compound is an archetypical glass-forming oxide. We present the in situ X-ray diffraction study of the pressure-temperature phase diagram of PO and of the liquid PO structure under high pressure up to 10 GPa. We found that structural transformation in the liquid PO under pressure is unique and includes three stages: first, the disappearance of the intermediate range order of the melt together with a slow increase in the average first-coordination number 
(P-O and O-P neighbors) up to 4 GPa; second, the "normal" compression almost without structural modification at higher pressures up to 8-9 GPa; and, finally, the abrupt change of the short-range order structure of the liquid with the jumplike increase at 9-10 GPa.
Brazhkin, V. V.*; Katayama, Yoshinori; Kanzaki, Masami*; Lyapin, A. G.*
Advances in Chemical Physics, Vol.152, p.29 - 50, 2013/04
In recent years, transformations in the melts of elementary substances and oxides have been found under high pressure. These transformations are accompanied by structural changes and variations in physical properties. In this work, structure and viscosity of Se, AsS, AsS, AsS
and BO were studied using synchrotron radiation. These substances exhibit changes in bonding in the crystalline state under high pressure. An X-ray diffraction measurements and falling sphere viscosity measurements using an X-ray radiography technique were carried out. Huge change in viscosity which accompanies structural change under compression was observed in each substance.
Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki
High Pressure Research, 33(1), p.191 - 195, 2013/01
Times Cited Count：5 Percentile：39.08(Physics, Multidisciplinary)Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki
Physical Review B, 86(17), p.174103_1 - 174103_9, 2012/11
Times Cited Count：26 Percentile：70.69(Materials Science, Multidisciplinary)Brazhkin, V. V.*; Katayama, Yoshinori; Kanzaki, Masami*; Kondrin, M. V.*; Lyapin, A. G.*
JETP Letters, 94(2), p.161 - 170, 2011/09
Times Cited Count：11 Percentile：58.38(Physics, Multidisciplinary)It is known that a number of compressed melts undergo structural phase transitions. Data on the structural changes at high pressures in chalcogenides (AsS, AsS) and oxide (BO) melts with a network structure have been reviewed. Viscosity is one of the fundamental physical properties of a liquid. For various melts, it varies in a very wide range. Structural transformations in melts induce the corresponding changes in all physical properties, in particular viscosity. The measurements of the viscosity of a number of melts at high pressures and temperatures by the radiographic method have been reported. Changes in the viscosity by several orders of magnitude have been detected when the pressure is varied by several gigapascals. The diffusion mechanism in network structure melts at various pressures has been analyzed.
O glassBrazhkin, V. V.*; Akola, J.*; Katayama, Yoshinori; Kohara, Shinji*; Kondrin, M. V.*; Lyapin, A. G.*; Lyapin, S. G.*; Tricot, G.*; Yagafarov, O.
Journal of Materials Chemistry, 21(28), p.10442 - 10447, 2011/07
Times Cited Count：17 Percentile：48.01(Chemistry, Physical)PO compound is an archetypical glass-forming oxide with a high hygroscopicity. We found that the quenching from the POmelt under ultrahigh pressures enables obtaining densified PO glasses with a residual densification up to 12% at normal conditions. These glasses have a low hygroscopicity and can exist under air conditions for several weeks. An examination of the structure of the new form of PO glass reveals a cardinal decrease of the volume of nanovoids in the glassy matrix.
S under high pressureBrazhkin, V. V.*; Katayama, Yoshinori; Kondrin, M. V.*; Lyapin, A. G.*; Saito, Hiroyuki
Physical Review B, 82(14), p.140202_1 - 140202_4, 2010/10
Times Cited Count：17 Percentile：58.6(Materials Science, Multidisciplinary)The AsS melt at room pressure represents a liquid having a three-dimensional network structure, semiconducting properties, and a huge viscosity. We have found that under high pressure a considerable change in the medium and short-range structure of this liquid is observed. Intermediate-range order correlations in the atomic arrangement almost disappear under pressure and an increase in the coordination number is observed.
O melt under high pressureBrazhkin, V. V.*; Farnan, I.*; Funakoshi, Kenichi*; Kanzaki, Masami*; Katayama, Yoshinori; Lyapin, A. G.*; Saito, Hiroyuki
Physical Review Letters, 105(11), p.115701_1 - 115701_4, 2010/09
Times Cited Count：51 Percentile：86.24(Physics, Multidisciplinary)Liquid BO represents an archetypical oxide melt with the cation coordination number 3 and unusual structural units - planar boroxol rings. It features super-high viscosity at melting temperature. The results of the 
X-ray diffraction study and viscosity measurements of the BO liquid under high pressure up to 8 GPa are presented. Additionally, the NMR study of BO glasses quenched from the melt at different pressures has been carried out. The number of the boroxol rings in the melt rapidly decreases with pressure. The viscosity of the BO melt along the melting curve drops by 4 orders of magnitude as the pressure increases up to 5.5 GPa and remains unchanged on further pressure increase.
-As
S realgar under high pressureTuktabiev, M. A.*; Popova, S. V.*; Brazhkin, V. V.*; Lyapin, A. G.*; Katayama, Yoshinori
Journal of Physics; Condensed Matter, 21(38), p.385401_1 - 385401_7, 2009/08
Times Cited Count：17 Percentile：57.91(Physics, Condensed Matter)The energy-dispersive X-ray diffraction technique has been employed to study the structure and equation of state of realgar AsS under pressures up to 8 GPa at room temperature. We have obtained pressure dependences of the unit cell parameters and volume for the monoclinic structure of realgar. At a pressure of around 7 GPa, realgar showed a polymorph transition to a new molecular phase with a supposedly orthorhombic structure. The phase transition is likely to be associated with the removal of a monoclinic distortion in the unit cell.
O glass under high pressureBrazhkin, V. V.*; Katayama, Yoshinori; Trachenko, K.*; Tsiok, O. B.*; Lyapin, A. G.*; Artacho, E.*; Dove, M.*; Ferlat, G.*; Inamura, Yasuhiro; Saito, Hiroyuki
Physical Review Letters, 101(3), p.035702_1 - 035702_4, 2008/07
Times Cited Count：74 Percentile：90.35(Physics, Multidisciplinary)We study polyamorphism of BO glass using X-ray diffraction up to 10 GPa in the 300-700 K temperature range, in situ volumetric measurements up to 9 GPa, and first-principles simulations. The glass undergoes two-stage transformations under pressure including a gradual increase of the first B-O (O-B) coordination numbers above 5 GPa. The fraction of boron atoms in the fourfold-coordinated state at P10 GPa is smaller than was assumed from inelastic X-ray scattering spectroscopy data, but is considerably larger than was previously suggested by the classical molecular dynamics simulations. The observed transformations under both compression and decompression are broad in hydrostatic conditions.
Brazhkin, V. V.*; Katayama, Yoshinori; Kondrin, M. V.*; Hattori, Takanori; Lyapin, A. G.*; Saito, Hiroyuki
Physical Review Letters, 100(14), p.145701_1 - 145701_4, 2008/04
Times Cited Count：44 Percentile：83.61(Physics, Multidisciplinary)An 
high-temperature high-pressure X-ray diffraction, resistivity measurements, and quenching from melt were performed on liquid chalcogenide AsS. The obtained data provide direct evidence for the existence three forms in the melt under compression: one is a moderate viscosity molecular liquid, the second one is a high-viscosity nonmetallic polymerized liquid and the third one is a low-viscosity metallic liquid. The two transformations occur at P 
1.6-2.2 GPa and at P 4.6-4.8 GPa. Upon rapid cooling, molecular and metallic liquids crystallize to normal and high-pressure phases, respectively, while a polymerized liquid is easily quenched to a new AsS glass. General aspects of multiple phase transitions in liquid AsS, including relations to the phase diagram of the respective crystalline, are discussed.
Brazhkin, V. V.*; Gavrilyuk, A. G.*; Lyapin, A. G.*; Timofeev, Yu. A.*; Katayama, Yoshinori; Kohara, Shinji*
Applied Physics Letters, 91(3), p.031912_1 - 031912_3, 2007/07
Times Cited Count：21 Percentile：61.45(Physics, Applied)A high pressure method to produce bulk chalcogenide glasses of a unique AsS composition has been developed. The structure, optical properties, and stability of the obtained glasses have been studied. Glasses have an intrinsic deep-red color, opticalpseudogap Eg
1.75 eV, a broad Urbach absorption tail W
120 meV, and high temperature stability up to 130
C. AsS glasses show photoinduced transformations, including photocrystallization. The glass structure is largely based on the quasimolecular AsS units with partial polymerization providing an example of an inorganic molecular-based glass.
and ZnCl halogenides under pressureBrazhkin, V. V.*; Lyapin, A. G.*; Popova, S. V.*; Katayama, Yoshinori; Saito, Hiroyuki; Utsumi, Wataru
Journal of Physics; Condensed Matter, 19(24), p.246104_1 - 246104_10, 2007/06
Times Cited Count：23 Percentile：67.31(Physics, Condensed Matter)Liquid AlCl and ZnCl halogenides are studied by high-pressure high-temperature X-ray diffraction measurements. These halogenides have a quasi-molecular network structure in liquid state at normal pressure. They are intermediate between pure covalent and ionic melts. The present study is indicative of a rapid and strong breakdown of an intermediate range order in a tetrahedral network of melts for the initial pressure range and points to rather sharp transitions in liquids with the formation of a short-range order structure similar to ionic melt structures. Such a two-stage structural transformation under pressure is the general feature for a wide class of simple melts, including most of the pseudo-covalent halogenides.
Brazhkin, V. V.*; Ekimov, E. A.*; Lyapin, A. G.*; Popova, S. V.*; Rakhmanina, A. V.*; Stishov, S. M.*; Lebedev, V. M.*; Katayama, Yoshinori; Kato, Kenichi*
Physical Review B, 74(14), p.140502_1 - 140502_4, 2006/10
Times Cited Count：49 Percentile：84.56(Materials Science, Multidisciplinary)Using two different high-pressure techniques, we have prepared boron-doped diamonds with atomic concentration of the dopant ranging from 0.04% to 4% (from 7
10
to 710
atom/cm
) and studied the lattice constants and thermal expansion of the diamonds in the temperature range from 90 to 300 K. Both sets of samples demonstrate the same increasing concentration dependence of the lattice parameter with maximum shift of the lattice constant about 0.011
. We have established an abnormally high thermal expansion of the heavily boron-doped superconducting diamonds with respect to the undoped ones and a nearly linear correlation between lattice constant and critical temperature of the superconducting transition.
, AlCl) under pressureBrazhkin, V. V.*; Katayama, Yoshinori; Lyapin, A. G.*; Popova, S. V.*; Inamura, Yasuhiro*; Saito, Hiroyuki; Utsumi, Wataru
JETP Letters, 82(11), p.713 - 718, 2005/12
Times Cited Count：11 Percentile：55.64(Physics, Multidisciplinary)The results of investigating the phase diagrams of ZnCl and AlCl halides, as well as the structure of the short range order of the corresponding melts under pressures up to 6.5 GPa, by the method of energy-dispersive X-ray diffraction are reported. When a ZnCl crystal is compressed, a phase transition occurs from the 
phase (HgI structure type) to the 
phase (distorted CdI structure, WTe type). The structural studies of the liquid state of ZnCl and AlCl indicate that the intermediate-range order decreases rapidly in the tetrahedral network of both melts as the pressure increases to 1.8 and 2.3 GPa for ZnCl and AlCl, respectively. With further compression, the transitions in both melts occur with a change in the structure of the short-range order and with an increase in the coordination number. In this case, the transition in AlCl occurs at about 4 GPa and is a sharp first order transition, whereas the transition in ZnCl occurs more smoothly in a pressure range of 2-4 GPa with a maximum intensity near 3 GPa. Thus the AlCl and ZnCl compounds exemplify the existence of two phenomena, gradual decay of intermidiate-range structural correlations and a sharper liquid-liquid coordination transition.
O under high pressureBrazhkin, V. V.*; Katayama, Yoshinori; Inamura, Yasuhiro; Kondrin, M. V.*; Lyapin, A. G.*; Popova, S. V.*; Voloshin, R. N.*
JETP Letters, 78(6), p.393 - 397, 2003/06
Times Cited Count：31 Percentile：77.51(Physics, Multidisciplinary)We present in situ (X-ray diffraction) and ex situ (quenching) structural studies of crystalline, liquid, and glassy BO up to 9 GPa and 1700 K, drawing equilibrium and nonequilibrium phase diagrams of BO, Particularly, we have determined the melting curve, the stability regions for crystalline BO and BO II modifications, the regions of transformations, such as densification or crystallization, for both the liquid and glassy states, including the region of sharp first-order-like transition in liquid BO to a high-density phase near 7 GPa. Quenching experiments also show that the transition to the high-density liquid can occur at much lower pressures in nonstoichiometric melts with an excess of boron. BO is the first glassformer whose transformations in the disordered state have been comparatively studied for both liquid and glassy phases.
Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki
no journal, ,
Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki
no journal, ,
Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki
no journal, ,
Gallium has a unique crystal structure which has Ga as building blocks. Many phases are found as function of temperature and pressure. The structure of liquid cannot be described as a simple hard-sphere model. In this study, details of structural changes of liquid under high-pressure and high-temperature conditions were investigated using modern measurement and analysis methods, reliable density data, a quasi-crystalline model and a reverse Monte Carlo method. The energy-dispersive X-ray diffraction measurements along the melting curve up to 5.3 GPa were carried using a cubic-type multi-anvil press installed on a JAEA beamline, BL14B1, in SPring-8. Structural change towards a simple-liquid like structure was observed.
