Ph.D. thesis (pdf) - dirac

72 Alpha Relaxation
the dielectric cell and the details of the electric connections were developed during
the course of this work. The specifications of the setup are not reported elsewhere,
and we will therefore present it in some detail below.
The cell and sample environment
The setup is depicted in figure 5.1. The pressure environment is based on liquid
compression using a commercial piston-and-cylinder device connected to the homebuilt
autoclave in which the dielectric cell is placed. The autoclave is cylindrical
with a diameter of 4 cm and a length of 15 cm. It has a wall thickness of 4 cm
and is made of metal . The dielectric sample cell is entered into the autoclave from
the end opposite the entrance of the compression fluid. Sealing of the autoclave is
accomplished with a metallic threaded conical piece and a system of metallic and
rubber o-rings. One of the major difficulties is to lead the electrical connections
of the dielectric cell out of the autoclave. This is done by leading two thin wires
through the metal closing piece. The wires are isolated from the metal by thin cones
of rezine. The pressure setup can resist pressures up to slightly above 400 MPa.
The pressure is measured using a strain gauge connected to the compression liquid
system.
Cooling is performed by flow of thermostated cooling liquid running inside the metallic
walls of the autoclave. The temperature and the temperature stability are monitored
by two Pt100 sensors. One is placed in the wall of the autoclave; the other
is emerged in the compression liquid and is at a distance of maximum 0.3 cm from
the sample. The connections to the second temperature control are led through
the walls of the autoclave with rezine isolation of the same kind as that used for
the electric connections of the dielectric cell. The temperature is held stable within
±0.1 K for a given isotherm. The temperature during the time it takes to record
a spectrum is stable within ±0.01 K. The accessible temperature range is 210 K to
340 K.
The capacitor used for the dielectric measurements is totally immersed in the sample
liquid, which is isolated from the compression liquid by a flexible Teflon cell. The
Teflon cell is cylindrical and closed with a threaded lead and a rubber o-ring. The
electric contacts to the electrodes are forced through the Teflon cell will which is approximately
1 cm at this point. In this system no mixing occurs between the sample
liquid and the compression liquid. The Teflon cell has the additional advantage that
the electrodes are electrically isolated from the metallic walls of the autoclave. The
Teflon cell is surrounded by the compression liquid from all sides and it has one end