Proceedings of the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.
ABOUT RADIATION HARDNESS OF THE NUCLEAR TECHNIQUE
ADVANCED CONSTRUCTION OXIDE MATERIAL
Abdukadirova I.Kh.
Institute o f Nuclear Physics, Tashkent, Uzbekistan
AI2O3 oxide (as of some oxide metals) is one of the perspective high-k electro-insulators and construction oxide materials, in particular, for the ceramical fuel material and for a first wall thermonuclear arrangement. Besides, this oxide is widely used as an active element or substrate at creation of laser and MOS systems, as a film coating and receiver of IR-radiation. Thus this work aims at investigation of radiation stability of the physical properties and a structure of AI2O3 oxide after irradiation in the reactor of a high fluence.
In this connection the peculiarities of radiation effect on lattice parameters ( a,c ), form and position of several reflections, reflection coefficient and frequency of valence and deformation oscillations of Al-0 bonds, electric characteristics of the oxide were studied with techniques of X-diffraction, dielectric and IR-reflection spectroscopy.
For example, in present communication the results of X-ray structure investigation of a after irradiation by high neutron doses (F) are reported. X-diffraction patterns were obtained using an X-ray diffractometer.
Particular attention was given to dynamics of form and positions some representative reflexes with hkl = 014, 110, 03.12 and etc. The diffraction patterns exposed essential changes of peak intensity and position depending upon F, the Bragg angle 2 0 decreases with an increase in dose, the regularity can be observed if Koci and K0C2 doublet is splintered. For example, figure 1
demonstrates to radiation dynamics of the function 2 0 (F) for this doublet (Koci and K a2) in the reflexes 03.12.
One can see from fig. 1 that the displacement of this peak is A(20) = 40-50° at dose F=1020- 1021 cm'2 (for the reflexes 02.10 - see table 1). At high doses the reflexes at 2 0 > 70° are eroded and weakened and doublets are not splitting, the lattice parameters of crystals (a, c, d/n) undergo anisotropy expansion (table 1), at very high dose this parameter does not change more than Ac= 0,0038 nm and Aa = 0,0014 nm.
Table 1. Influence of neutrons on some parameters of crystals.
F, cm'2 5.1016 1.1017 5.1017 1.1018 5.1018 8.1018 Di, a.u. 0,18 0,27 0,34 0,62 1,29 1,29 D2, a.u. 0,10 0,12 0,15 0,35 0,51 0,64 F, cm'2 8.1018 1.1019 5.1019 8.1019 1.1020 5.102° Di, a.u. 1,29 1,27 1,28 1,70 1,95 2,15 D2, a.u. 0,64 0,93 1,05 1,00 1,21 1,99 c, nm 1,298 1,298 1,298 1,299 1,300 1,301 d/n, nm 0,2379 0,2379 0,2380 0,2381 0,2383 0,2386 (20)° 89,04 89,03 88,99 88,98 88,95 88,86
Besides, it is shown that at such doses some halo appears at the diffraction patterns. In table 1 dose dependence of generation in the absorption spectra bands at 257 and 358 nm (F- and F- aggregate defects) is given. The mechanism of atom displacement out of lattice knots plays the main role in radiation damage of high doses irradiation crystals.
Section I. Nuclear Energy: Present Status and Perspectives
Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.
Fig. 1. Dose dependence of the function 2 0 (F) for the doublet Kocı (1) and Kot2(2) of reflexes 03.12
The optical characteristics - a reflection coefficient and frequency of valence (736, 614 cm'1) and deformation (464 cm'1) oscillations of Al-0 bonds of the oxide were studied with techniques of IR-reflection spectroscopy in region of 400-1200 cm'1. The partial decrease of intensity ( R ) and frequency ( v ) of this modes at fluence 8.1019 cm'2 was observed. The change of these
jQ 2
parameters was observed at a neutron fluence (6-8). 10 cm' .
Some change of these optical (valence and deformation oscillations of Al-0 bonds ) and structural parameters ( the lattice parameters of crystals ( a, c, d/n ) and positions of some representative reflexes, peak intensity and the Bragg angle ), a density and a linear size of irradiated samples were found near a neutron fluence 10 cm' and 10" cm' , but the structure state remained stable at the following increase of the irradiation dose ( at F= 1.1021 cm'2 and 7.1021 cm'2 and higher ).
Features of dose and temperature dependencies of electric properties (a, s, tg5) were determined after irradiation at different doses of ionizing radiation. Increase of the dielectric permittivity and IR-transmittance was found near temperatures (25-400 °C) and high doses. Besides, at a gamma-dose of 103-105 Gy the electric conductivity decreases.
The opportunity of describing dependence a(T,D) in irradiated AI2O3 oxide through the
analytic equation, consisting of the exponential and power functions with corresponding coefficients has been showed. The values of those coefficients in the temperature range where the a (irradiation stimulated) is prevailing, were calculated. It was determined that the coefficients of UF-46 alumina ceramics are in acceptable agreement. It is clear that the result is very interesting, because it certifies that the a in reactor irradiated ceramics was determined mostly by the gamma-irradiation, influencing on the crystal phase of ceramics.
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Proceedings of the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.
1,5
2,0
2,5 103/T,l/K
Fig 2. The dependence g(T) of samples before (1) and after(2) irradiation
Irradiation to dose D=104 Gy leads to a decrease, however the shapes of the g i(T)
dependencies for samples N 1 and N 2 type (cut parallel and normal on the main optical axis) after gamma-irradiated are alike (table 1, fig. 2).
Table 2. Temperature dependence of the electric conductivity of the samples before (g0) and after (g i) irradiation T,°C GcfT’m' 1 GuQ 'W1 1 0 0 9,6.10' 12 1,4.10 ^ 150 3,9.10' 11 2,9.10‘ 12 250 9,6.10' 10 1,2.1 O' 10 350 1,1.1 0'* 9,5.10‘1U 400 2,4.10‘8 7,7.10‘9
Activation energies (E) of conductivity for the low- and high-temperature regions were calculated for samples - Ei and E2 respectively (table 3).
Table 3. Activation energy for the electrical conductivity of gamma irradiated corundum
Dose, Gy T,°C Ei, eV T,°C E2, eV
O < 150 0,29 > 150 0 , 6 8
1 0 4 <150 0 , 2 0 >150 0,78
Experimental dependence of g(T, D) for single crystals of AI2O3 oxide at T<150°C and
T>150°C gamma-irradiation demonstrate no practical influence on the activation energy. This indicates on retain at the irradiation of character conductivity of the crystals.
As to some increase in E2 for irradiated samples (in the high temperature region) we can say,
that in the case of T>Tb apart from low-temperature conductivity there is the conductivity conditioned by, for example, the motion of oxygen ions via the lattice vacancies, which according to Dince makes the conductivity mechanism better at the temperatures higher then room temperature.
Section I. Nuclear Energy: Present Status and Perspectives
Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004. The proximity of gained results for activation energy of conductivity for gamma-irradiated crystals E2 to the activation energy of the reactor irradiated UF-46 ceramics indicates on the additional fact certifying the most contribution to conductivity of crystalphase.
The dose dependencies of the conductivity in this plates were found to be nonmonotonic. For example, the minimum on the curve g(D) in samples JV2 1 and JV2 2 at D=105 Gy is marked.
These temperature-dose kinetics of the dependence g(T, D) for the temperatures 25-100°C were established.
So, for the first time it is established that the g(D) curve has the extremums, because of at 10
5 Gy dose it passes though the minimum. It is interesting that at the doses of D>10 6 Gy initial conductivity behaviour of samples is restoring.
The problems connected with the possible causes are established based on the peculiarities of kinetics in the position of the existing models and discussed on the base of these characteristics analysis.
Based on the obtained results we draw the conclusion that the discovered unusual effect of radiation modifications of AI2O3 oxide crystals electric properties, when the g increasing till the
105 Gy, i.e. electroinsulators properties are improved and at the dose >106 Gy - initial conductivity behaviour of samples is restored -indicates the reason to propose to use the AI2O3
oxide based electronic materials in the high radiation environment.
Thus, such thermal-radiation treatment may serve as a method leading to the permittivity growth at elevated irradiation doses and temperatures, decrease and imorovement of several electric, mechanic and optic characteristics. This is testified to prospect of application of this high-k oxide ( AI2O3 oxide ) in a composition at other oxide metals in the quality construction,
insulation and fuel materials in the reactor, cosmic and semiconductor technique, under the condition of irradiation influence.
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