Dielectric Spectroscopy

Description, Specification, The principle, Integration with external stimuli, Current setup

[Photo: PI1 Uni Stuttgart]

Specifications

Frequency range

Agilent 4294A Precision Impedance Analyzer: 40Hz - 110MHz

Novoncontrol Alpha-A High Resolution Frequency Analyzer: 3μHz – 40MHz
Temperature range

Cryovac He-Konti Magno Cryostat: 2K – 325K
Magnetic field range

Oxford Spectromag Superconducting Magnet: - 9T – + 9T
Pressure range

Almax easyLab Diamond Anvil Pressure Cells: 0GPa – 15GPa
Voltage range

Novocontrol HVB 300 High Voltage Interface: 150V

aixACCT TF Analyzer 2000 + 400V High Voltage Amplifier: 400V

General Description

Dielectric spectroscopy is the study of dynamics in matters in domain of frequency from 10−6 to 1012 Hz together with a variety of stimuli. This extended range of frequency covers the characteristic time-scales of electronic, molecular and dipolar relaxations, the conducting charges transport behaviours, polarizations within the interfacial areas in the crystal structures, etc. Henceforth, dielectric spectroscopy determines the collective dielectric properties of the molecular systems, and more microscope details can be dissected with the application of extra stimuli, like magnetic fields and physical pressure.
Fig. 2: Dielectric spectroscopy setup
Photo: PI1 Uni Stuttgart
Fig. 3: Metallic contacts on samples as the capacitors
Photo: PI1 Uni Stuttgart
Fig. 1: Schematic of the auto-balancing bridge method from ref. [1]

Principle

The primary quantity being determined is the complex dielectric permittivity Ԑ* = Ԑ´ + i Ԑ". There are plenty of approaches in measuring  Ԑ*  of the sample, with feasibility depends on the favoured frequency range and sample conditions. One of the most intuitive and widely deployed approach is the auto-balancing bridge method, in which the crystal is sandwiched by electrodes and its complex admittance Y = G + iB is measured by a balanced bridge circuit.

 

 

With the admittance and geometric factor of the sample known, other electrical quantities can subsequently be calculated, such as the conductivity (Fig. 4) and the dielectric permittivity (Fig. 5). Dielectric spectroscopy simultaneously probe the conduction and dipolar polarizations in the sample, and so it can provide a consistent overview of the electronic nature of the system.

 

 

Fig. 6: Superconducting magnet
Photo: PI1 Uni Stuttgart
Fig. 7: Diamond anvil cell
Photo: PI1 Uni Stuttgart
Fig. 8: High voltage amplifier and analyzer
Photo: PI1 Uni Stuttgart
Fig. 4: Conductivity of BaFe2S3 and BaFe2Se3 [2].
Fig. 5: Dielectric permittivity of BaFe2S3 and BaFe2Se3 [2]

Integration with external stimuli

The microscopic origin of the electronic properties can be dissected by tracking down their evolutions with the environment, e.g. under magnetic field and under physical pressure. Our laboratory is well-equipped with external stimuli devices (Fig. 6-8), allowing a comprehensive study of the material properties under extreme conditions. On top of that, these stimuli can be incorporated and operated simultaneously, namely, multiple extreme conditions can be realised in case of any interest.

References

[1] F. Kremer and A. Schönhals, eds., Broadband Dielectric Spectroscopy. Springer Berlin Heidelberg, 2003.
[2] Y. T. Chan, S. Roh, S. Shin, T. Park, M. Dressel, and E. Uykur, “Three-dimensional hopping conduction triggered by magnetic ordering in the quasi-one-dimensional iron-ladder compounds BaFe2S3 and BaFe2Se3,” Physical Review B, vol. 102, jul 2020.

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