Position: Head Scientist About: Dr. Sinitsyn was graduated from the Faculty of General and Applied Physics of Moscow Institute of Physics and Technology in 1984 (diploma: "Pressure-Temperature phase diagram of superprotonic conductor CsHSO4"). Since then, he has worked at the Institute of Solid State Physics RAS. He got a PhD degree in Physics and Mathematics in 1990 (dissertation: “Pressure effect on phase transition and protonic conductivity in crystals with hydrogen bond network“) and a Dr. Sci. degree in 2014 (dissertation: "Dynamical and static disorder in solids under high pressure").

Visiting positions:

•  Laboratoire Leon Brillouin (LLB), Saclay, France, 1999;

•  Darmstadt University , Solid State Department, Germany, 2001-2003.

•  The European Synchrotron Radiation Facility (ESRF), Grenoble, France, 2001;

•  Institute Laue-Langevin ( ILL ), Grenoble, France, 2002;

•  Synergy Ceramics Laboratory, FCRA, Nagoya, Japan, 2004-2005.

Areas of expertise :

•  Protonic conductors of solid acid sulfates and selenates crystals (transport properties, phase transitions, dielectric relaxation);

•  Application of solid state ionic conductors (fuel cells, electrochemical cells for NO_x decomposition);

•  Structural and physical properties of ice and water;

•  Phase transitions and solid state amorphization under high pressure.

Number of papers in refereed journals: over 50

Research activities:

1. Phase transitions in superprotonic MeHAO₄ and Me₃H(AO₄)₂ (where Me = Rb, Cs, NH4; A = S, Se) crystals were studied at high hydrostatic pressures. An analysis of the P-T phase diagrams of these substances revealed the occurrence of some general trends in the baric dependences of the melting temperature and superprotonic transition temperature. This allowed predictions of the location of stability fields of superionic phases in the diagrams of a large variety of yet unexplored systems. High-pressure investigations of NH₄HSO₄ and RbHSO₄ well corroborated the predictions.

2. Large samples of a few high-pressure phases of water ice have been for the first time recovered at ambient pressure by quenching at high pressure to liquid nitrogen temperature. These were high-density amorphous ice ( hda ), ice VI, ice VIII and a new form of ice, "defective" ice VI'. Studies of the quenched samples by inelastic neutron scattering showed a close similarity in the vibrational spectra of the hda ice and ices VI and VI' that points to the essentially the same atomic correlations and force constants in these phases.

3. The available experimental data on the properties of supercooled water and on the parameters of the I-st order phase transition lda ® hda between the low-density and high-density amorphous phases of water ice were analysed using a two-level thermodynamic model. The transition was shown to terminate in a critical point at 173 atm and -43°C. Thus, water proved to have a second critical point. Every feature of water at ambient pressure including the maximum density at 4°C was quantitatively described as a supercritical anomaly of the lda « hda phase transformation.

4. It is widely accepted that solid-state amorphization can occur as an intermediate stage of a polymorphic phase transition delayed by kinetics reasons. A structural study Cu₂O heated at a pressure of 30 GPa (diamond-anvil cell, synchrotron radiation) revealed the following sequence of phase transitions:

hexagonal phase amorphous state nanocrystalline mixtureof CuO and Cu crystalline CuO + Cu mixture.

This has been for the first time that solid-state amorphization proceeded as an intermediate stage of decomposition of a compound. Estimates show that this new type of amorpization should be characteristic of many complex compounds and minerals in the Earth crust.

Office Address: Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Moscow Region, RUSSIA.

Office Phone: 2-52-46 (local)
FAX: 007-(095)-576-41-11 (ISSP office)

e-mail: sinitsyn@issp.ac.ru

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