Gamma Irradiation Effects in InBi0.8Te0.2 Crystals Grown by Horizontal Directional Freezing

doi:10.1007/s40195-015-0314-9

Abstract

Abstract:

The high-energy gamma-ray irradiation treatment using Co-60 isotope offers the possibility of engineering mechanical and optoelectronic properties of InBi_0.8Te_0.2 crystals. Tellurium-doped indium bismuthide (InBi) crystals were prepared by horizontal directional freezing technique. Dose-dependent modifications in structure, composition and surface topographical features have been analyzed by X-ray powder diffraction, X-ray energy-dispersive analysis, transmission electron and atomic force microscopy, respectively. Dielectric constant and dielectric loss were found to increase with the cumulative dose of radiation, and a shift in the ferroelectric transition temperature (T_c) from 405 to 410 K was observed for 25 kGy. Upon irradiation, there is an enhancement in microhardness (H_V), yield stress (σ_y) and stiffness constant (C₁₁). The optical transmittance was decreased by 12.45%, resulting in a reduction in the optical band gap from 0.210 eV to 0.198 eV. These results indicate the suitability of InBi_0.8Sb_0.2 crystals for low-wavelength infrared applications.

Key words: Crystal growth, Dielectric properties, Optical properties, Hardness, Irradiation

C. J. Ajayakumar, A. G. Kunjomana. Gamma Irradiation Effects in InBi_0.8Te_0.2 Crystals Grown by Horizontal Directional Freezing[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(10): 1205-1213.

Figures/Tables 13

Fig. 1 X-ray diffractograms of pristine- and gamma-ray-irradiated InBi0.8Te0.2 crystals

Table 1 The lattice parameters of pristine and irradiated crystal

Dose (kGy)	a = b (10^-1 nm)	c (10^-1 nm)	c/a	Volume (10^-3 nm³)	Crystal structure
0	4.9892	4.7823	0.9585	119.04	Tetragonal
10	4.9892	4.7823	0.9585	119.04	Tetragonal
15	4.9892	4.7824	0.9585	119.04	Tetragonal
20	4.9890	4.7825	0.9586	119.03	Tetragonal
25	4.9899	4.7820	0.9583	119.06	Tetragonal
30	4.9892	4.7824	0.9585	119.04	Tetragonal

Fig. 2 TEM micrographs exhibiting a strained region (direct magnification 68000×), b defects (direct magnification 4100×) in the gamma-ray-irradiated InBi0.8Te0.2 crystals

Fig. 3 AFM images of 2D profile a of scan dimensions 1 μm × 1 μm demonstrating strained regions in the crystal lattice and 3D profile b (2.54 nm × 2.54 nm × 1.95 nm) exhibiting growth hillocks

Fig. 4 SEM-EDAX spectra of pristine a and 25 kGy b irradiated InBi0.8Te0.2 crystals

Fig. 5 Plots of frequency versus dielectric constant a and frequency versus dielectric loss b for InBi0.8Te0.2 crystals irradiated with gamma radiation

Fig. 6 Plots of temperature versus dielectric constant a and temperature versus dielectric loss b of InBi0.8Te0.2 crystals subjected to 25 kGy gamma-ray dose for various frequencies

Fig. 7 Variations of AC conductivity with temperature for 25 kGy gamma-ray-irradiated InBi0.8Te0.8 crystals at various frequencies

Fig. 8 Variations of microhardness (HV) with the applied load (P)

Table 2 Hardness parameters

Sample	H_V (kg/mm²)	n	σ_y (kg/mm²)	C₁₁ (kg/mm²)
InBi_0.8Te_0.2 (pure)	15.4	2.47	9.322	119.7
InBi_0.8Te_0.2 (irradiated)	16.8	2.62	14.25	141.2

Fig. 9 Plots of log P versus log d of pure InBi0.8Te0.2 crystals a and InBi0.8Te0.2 crystals irradiated with 25 kGy gamma-ray dose b

Fig. 10 Plots of (αhγ)2 versus photon energy (hγ) of the as-grown and irradiated InBi0.8Te0.2 crystals

Fig. 11 Transmittance spectra of pristine- and gamma-ray-irradiated InBi0.8Te0.2 crystals

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