The Effect of X‐Ray Irradiation on Conductivity of C and 2C Polytype TlInS2 Ferroelectrics

Abstract

The influence of X‐ray irradiation on DC conductivity of TlInS2 C and 2C polytypes is studied in the temperature range of 100–300 K. The X‐ray irradiation (absorbed doses are 0.9 and 2.7 kGy) leads to an increasing conductivity of both C‐ and 2C‐samples in proportion to the absorbed dose; the conductivity decreases on cooling in the temperature region of 100–300 K. An anomalous increase in conductivity is observed in C‐polytype samples on cooling in the temperature range of the incommensurate phase (197–214 K). The X‐ray irradiation causes the “blur” of that anomaly. It is established that the mechanism of hopping conductivity with variable hopping length takes place for both polytypes in the temperature range of 125–175 K, and the densities of localized states near the Fermi level (NF) are determined. Under irradiation, the density NF increases from 3.7 × 1018 eV−1 cm−3 (C) to 6.9 × 1018 eV−1 cm−3 (2C) and exceeds the initial value more than three times at D = 2.7 kGy. Using the 1D Kroning–Penney model, the role of incommensurate periodic potential in modification of electron band structure at creation of the incommensurate phases in crystals is discussed.