a. Complex dielectric permittivity and dielectric relaxation

This technique enables access to the real and imaginary parts of the dielectric permittivity from 8 K to 900 K, and in the frequency range 2 Hz up to 2 MHz. Measurements can be made as a function of the ac measuring voltage (50 mV to 5 V) and of the an external voltage up to 40 V.

Moreover, dielectric relaxation can be carried out at fixed temperature by sweeping frequency (2 Hz to 2 MHz).

Experimental run and data acquisition is fully automatic.

Available equipment: Impedance meters and multimeters.


b. Thermal stimulated currents and polar relaxation

This technique is addressed to carry out measurements of currents that are originated by temperature changes. This is most attractive in those materials exhibiting electric polarization that changes with temperature. Some examples for this type of materials are: Multiferroics, magnetoelectrics, ferroelectrics, relaxors, electrets and micro- and nano-scale heterostructures of these materials. In this technique a constant temperature rate is fixed and the current measured using a short-circuit method.

Available equipment: Electrometers and multimeters.


c. Polarization inversion, and hysteresis cycles

This technique is used at fixed temperature and the signals are obtained from a modified Sawyer-Tower circuit. The electric polarization/electric field curves can be obtained. Materials showing non-linear behaviour are adequately studied with this technique, in particular those exhibiting ferroelectric ground states.

Available equipment: ac power supplies (frequency and amplitude as adjustable parameters and digital oscilloscopes.


d. Specific heat

The heat capacity is measured in an ARS Cryocooler, between 8 and 300 K, in a quasi-adiabatic fashion by means of an impulse heating technique. Experimental run and data acquisition is fully automatic.


e. Magnetic susceptibility

AC magnetic susceptibility (15K to 300K); external magnetic field from 0 to 300 G; frequency between 20Hz and 40000Hz. Acquisition of data are computer-controlled.


f. Temperature control and measurement

The temperature is changed and controlled using close-cycle cryostats (8 K – 350 K) and Linkam furnaces (80 K – 900 K). The temperature precision is ~0.1 K.

Measurements procedures and acquisition of data are computer-controlled.


g. Dielectric Spectrometer

The dielectric spectrometer system enables access to the real and imaginary parts of the dielectric permittivity and consists of a high resolution dielectric analyzer ALPHA. This equipment possesses a broadband dielectric converter with high input impedance on the entry and displays a resolution of ~1E-5. This system is also controlled by computer connected by a GPIB interface. To analyze the result one can resort to several software namely Windet, Winplot, and WinFLIT WINTEMP, also available at our facilities.

Characteristics of the system:

  • Temperature range: 80 K to 700 K;
  • Frequency range: 0.3 microHz- 1MHz;
  • Control temperature: System FOUR;
  • Stabilized power supplies;
  • Nitrogen Dewar;
  • Heating Module;
  • Cell sample with gold electrodes.
 Contact person: amalmeid@fc.up.pt