Department of Experimental Techniques

Creation of the device for the physics/chemistry investigations and technology.

Experimental investigations properties of substances(equation of states, structure) at high pressures by:

i - adiabatic pressure pulse technique, various versions of thermal analysis,

ii - neutron elastic/unelastic scattering, transmission,

iii - X-ray diffraction.

adiabatic pressure pulse technique

Measurement of the temperature response of the sample due to a small(15MPa) adiabatic pressure change(modulation) - determination of the derivative (T/P)s . Knowledge (T/P)s as a function of temperature and pressure allows to construct the family of adiabats, and to calculate the thermodynamic function.

Dzhavadov L.N.,Krotov Ju.I.,Prib.Tekh.Eksp.,1985,vol.3,pp.168-171.

m Experimental technique for measurement (T/P)s of solids and liquids up to 3.0GPa.

Dzhavadov L.N., Fiz.Tverd.Tela.,1985,vol.11,pp.3310-3314.

Heat capacity and thermal expansion of Sr under pressure.

Dzhavadov L.N., Zh.Fiz.Khim.,1987,vol.61(4),pp.1106-1108.

Determination of the thermodynamic properties from measurements of (T/P)s

Dzhavadov L.N.,High Temp.-High Press.,1989,vol.21,pp.401-405.

The temperature and pressure dependencies of (dT/dP)s near the - transformation of cerium

have been determined in the temperature range 300-700K and at pressures up to 3GPa.On the

basis of these data, the family of adiabats of cerium in the region of the critical point has been

calculated.

versions of thermal analysis

Thermal Analysis, Differential Thermal Analysis,Thermobaric Analysis.

The thermobaric analysis based on monitoring the excess pressure in the cell brought about under heating. This method is a sensitive indicator of the volume change at phase transition.

Dzhavadov L.N.,Instr. and Exper. Tech.,1996,Vol.39,No6,pp.861-864.

A cylinder-piston high-pressure apparatus with a useful volume of 10cm3. The maximum

pressure under piston for a solid compressed medium is 4.5GPa. The pressure

and temperature are controlled with a computer. Thermobaric Analysis.

neutron elastic/unelastic scattering, transmission

(collaboration with Russian Scientific Centre “Kurchatov Institute).

High pressure equipment for neutron studies (elastic & unelastic scattering, transmission of neutrons) is developed and created. Specimens (including highly compressible media, even such as molecular hydrogen) of volumes 0.5 to 20 ccm can be studied at temperatures 4.2 to 300 K and pressures 0 - 25 kbar. High pressure vessels which are optimised to experimental conditions are manufactured from highly durable aluminium alloys, from Ti-Zr alloy and from Cu-Be alloy. Pressure transmitting media can be liquid freons, heavy water, solidified gases etc.

Apparatus for Neutron Texture & Stress Analyses. The high-temperature apparatus for uniaxial compression at forces up to 150 KN under pressure to deform crystalline samples of volumes up to 20 ccm at temperatures up to 800 K is now situated at beam 7 of IBR-2 pulsed reactor in Dubna.

The crystal structures and phase diagrams of Li, Na & K were studied in the pressure range up to 3 GPa and temperatures 4.2120 K, new phase and non-trivial slope of phase transition line having been detected. [See: V.G.Vaks, A.A.Chernyshov V.F.Skok,. et.al., J.Phys.: Condens.Matter 1, 5319 (1989)]

The experimental equations of state of solid p-H2 and o-D2 have been determined [See: S.N.Ishmaev, I.P.Sadikov, A.A.Chernyshov. et.al., Sov.Phys.JETP 57, 228 (1983), Sov.Phys.JETP 62, 721 (1985),]

Search for zero defects existence in solid p-H2 was made. [See: B.A.Vindryaevskii, S.N.Ishmaev, N.M.Parovik et.al., Sov.Phys.JETP 77,509(1993),]

The short range order and the structure in liquid and solid isotopic solutions (p-H2)x(o-D2)1-x were investigated, weak tendency toward isotopic separation having been noted. [See: S.N.Ishmaev, I.P.Sadikov, A.A.Chernyshov. et.al., Sov.Phys.JETP 68,1403 (1988), Sov.Phys.JETP 75, 382 (1992).]

Various characteristics of solid p-H2 vibration spectrum (generalised anharmonic phonon density function, one-particle molecule mean kinetic energy, molecules mean square displacements etc.) have been determined in wide density range: 26.1850.78 nm-3. [See: B.A.Vindryaevskii, S.N.Ishmaev, G.V.Kobelev et.al., Sov.Phys. J.Low Temp Phys. 15,258(1989), G.V.Kobelev, V.A.Sukhoparov, A.S.Telepnev et.al., High Pressure Res. 14,111(1995), B.A.Vindryaevskii, S.N.Ishmaev, I.P.Sadikov et.al., JETP Lett. 62, 822 (1995).]

X-ray diffraction

(collaboration with Russian Scientific Centre “Kurchatov Institute).

The combination of energy-dispersive X-ray diffraction (EDXD) with synchrotron radiation (SR) and diamond anvil cell (DAC) allows rapid acquisition of crystallographic information from microscopic samples subjected to extreme static pressures (up to 2 MBar). For this aime special DAC is developed, in which the force on the piston is generated by pressurised helium, which pushes the membrane. It permits fine control and adjustment of the force applied to anvils, spatial stability of the sample under varying pressure and axial thrust. It is possible to reach low temperatures by use of rather helium refrigerator or a cryostat on cold helium gas flowing. Elevated temperatures are achieved in DAC by means of resistively heated furnace assembly. Special gas loading system permits to work with cryocrystals.