  The recently discovered ferroelectric nematic liquid crystals have been
reported to exhibit very large dielectric permittivity values. Here, we report
a systematic investigation of the dielectric behavior of a prototypical
ferroelectric nematogen by varying the thickness of the parallel capacitor
measuring cell. While in the non-polar high temperature nematic phase results
show only slight differences due to slight variations of the alignment, the
measured permittivity values in the ferroelectric nematic phase show a linear
dependence on the cell thickness. It is also shown that the characteristic
relaxation frequency decreases inversely proportionally to the thickness. The
results are discussed in terms of three different available models based on
different underlying mechanisms, accounting for cancellation of the probe
electric fields by polarization reorientation or by ionic charges, or based on
a recently proposed continuous phenomenological model.
