# Background dielectric permittivity: material constant or fitting parameter?

## TL;DR

This paper critically examines the concept of background dielectric permittivity, arguing that it cannot be consistently defined as a material constant or fitting parameter despite its usefulness in phenomenological models.

## Contribution

It provides a critical analysis of the background dielectric constant concept, highlighting its limitations in self-consistent physical modeling.

## Key findings

- Background dielectric constant is useful but not a true material constant.
- It cannot be introduced in a self-consistent manner.
- The distinction between critical and non-critical polarizations is discussed.

## Abstract

The concept of background dielectric constant proposed by Tagantsev, together with the distinction between critical and non-critical electric polarizations as a natural extension for the order parameter of ferroelectric phase transitions, is critically discussed. It is argued and exemplified that, even if these quantities can be very useful for obtaining qualitative and semi-quantitative results from phenomenological modeling, they cannot be introduced in a self-consistent manner.