Cz Gorecki, T Gorecki, M Kostrzewa - Thermal stability and kinetics of structural transformations in vitreous chalcogenide semiconductors - страница 1

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ВІСНИК ЛЬВІВ. УН-ТУ

Серія фіз. 2009. Bun. 43. С. 43-48

VISNYKLVIV UNIV. Ser. Physics. 2009. Is. 43. P. 43-48

PACS number(s): 74.70.Ad: 79.75.+g;71.23.Cq

THERMAL STABILITY AND KINETICS OF STRUCTURAL TRANSFORMATIONS IN VITREOUS CHALCOGENIDE SEMICONDUCTORS AsxSeioo-x AS STUDIED BY DIFFERENTIAL

THERMAL ANALYSIS AND EXOELECTRON EMISSION

METHODS

Cz. Gorecki1, T. Gorecki2, M. Kostrzewa1

'Department of Physics, Opole University of Technology 75 Ozimska Str., PL 45-370 Opole, Poland e-mail: c.gorecki@po.opole.pl 2Institute of Physics, Opole University

48 Oleska Str., PL 45-052 Opole, Poland

Kinetics of phase transitions in y-irradiated and non-irradiated chalcogenide glasses AsxSe100-x (x = 10, 20 and 30) has been investigated by parallel differential thermal analysis (DTA) and exoelectron emission (EEE) measurements. Activation energies for the retrification process in investigated materials have been determined by the Ozawa method. It has been found that the activation energy for retrification process in the surface layers is smaller than that for the retrification in the volume. Gamma-irradiation improves the thermal stability of investigated materials.

Key words: chalcogenide glasses, DTA, exoelectron emission, activation energy, retrification, y-irradiation.

Vitreous chalcogenide semiconductors, obtained by melting together the elements from the IV and V group of the periodic table of the elements with chalcogens (S, Se, Te), remain to be a subject of intensive investigations because of unusual combination of their physical properties. The most stimulating factor for these studies steams from potential applications of these materials, e.g. in optoelectronics [1]. These promising applications of chalcogenide glasses are, however, limited by their structural instability, resulting from the production process, in which the liquid phase is quenched to the ambient temperature [2]. The process of thermal ageing of the as-quenched material (e.g. long-lasting isothermal ageing at proper temperature) leads to the achievement of the metastable state characteristic of the overcooled liquid [1].

The ageing process of chalcogenide glasses can be stimulated by y-irradiation [3-6,15-16]. The effect of irradiation is an additional factor complicating the control of production of materials with desired (prognozed) properties.

Amorphous materials tend to crystallize at a proper combination of temperature and time. The stability of the chalcogenide glasses may be characterized by the activation energies and temperature of the thermally activated retrification and crystallization processes. There is an additional complicating factor caused by the fact, that the parameters determining the thermal stability of the volume and of the surface

© Gorecki Cz., Gorecki T., Kostrzewa M., 2009

layer of amorphous materials may differ among themselves. About 20 years ago we elaborated a method [7] for determination of the thermal stability for both the surface and volume of amorphous materials by parallel measurements of the temperature dependencies of the DTA signal and the intensity of photostimulated EEE. This method has been already successfully applied in investigations of the kinetics of phase transformations in some chalcogenide glasses [8, 9] and in amorphous selenium [10].

The aim of the present communication is to report the results of investigations of the kinetics of phase transformations and of the thermal stability of chalcogenide glasses AsxSe100-x (x = 10, 20 and 30) as well as the effect of y-irradiation on these processes and their parameters.

The vitreous samples of AsxSe100-x (x = 10, 20 and 30) chalcogenide glasses were prepared by the melt quenching method using a mixture of high purity precursors sealed in evacuated quartz ampoules (~10-3 Pa). The furnace was rocked to obtain homogeneous melt. The ingot was quenched at the ambient temperature and then annealed additionally near Tg point to remove the residual mechanical stresses. The amorphous state of chalcogenide glasses was controlled by a visible character of cinch­like fracture, data of X-ray diffraction analysis and transmission IR microscopy.

The DTA and EEE measurements were performed for two different types of samples: a - for samples not submitted to any excitation (irradiation) prior to measurements, and b - for y-irradiated samples (Co60 source, energy of y quanta 1,25 MeV, dose 2,06 MGy).

Measurements of the temperature dependencies of photostimulated exoelectron emission (EEE) intensity were carried out by means of the arrangement described in [11]. An open air point counter with saturated ethanol quenching vapor was used for detecting the exoelectrons. The sample temperature, controlled using an Ni-CrNi thermocouple with an accuracy of about 5 K, was changed at four constant heating rates (2, 5, 10 and 20 K/min). The sample surface was irradiated during the measurements by unfiltered radiation from a quartz lamp with a Q-400 burner.

The calorimetric investigations of the volume retrification were performed at five heating rates (1, 2, 5, 10 and 20 K/min) using the NETZSCH DSC 404/3/F differential calorimeter with E-type thermocouple using an empty crucible made of high density Al2O3 as references. All the EEE and DTA measurements were performed in air under ambient pressure.

Temperature dependencies of the intensity of photostimulated exoelectron emission (EEE) and of the differential thermal analysis signal (DTA), from non-irradiated (a) and y- irradiated (b) chalcogenide glasses AsxSe100-x, all measured at the same heating rate of 5 K/min. are shown in fig. 1. The parameter of the curves presented in this figure is the arsenic content (x) in the sample. The temperature dependencies of the intensity of exoelectron emission presented in fig. 1 display a maximum coinciding with the endothermal effect occurring on the DTA curves. The temperatures of these anomalies occurring on both the EEE and DTA curves systematically increase with increasing of the arsenic content in investigated samples. The process responsible for the effects displayed by EEE (surface sensitive method) and DTA (volume sensitive method) is the retrification process occurring in the surface layer and in the volume of investigated sample, correspondingly.

THERMAL STABILITY AND KINETICS...

1        ■ 1

Ь 30^-

JO

 

 

 

 

 

 

10 V_

 

 

a

 

 

 

3<^/4---

 

 

 

 

 

350 450

350 450

Т{К)

Fig. 1. Temperature dependencies of the DTA signal and exoelectron emission intensity from non-irradiated (a) and y-irradiated (b) chalcogenide glasses AsxSe100-x determined at a heating rate of 5 K/min. Parameter - As-content (x) in the sample

1           ' 1

b -/V.

20 JX//^S^

 

 

10 __

 

 

 

 

 

 

2

 

350 450        350 450 T |K]

Fig. 2. Temperature dependencies of the DTA signal and the intensity of EEE from non-irradiated (a) and y-irradiated (b) As30Se70 samples. Parameter - heating rate in K/min

Figure 2 represents the temperature dependencies of the DTA signal and of the intensity of photostimulated exoelectron emission (EEE) from non- irradiated (a) and y-irradiated (b) chalcogenide glass As30Se70, measured at different heating rates. The parameter of the curves shown in fig. 2 is the heating rate in K/min. The temperature of the anomalies occurring on the DTA and EEE curves presented in fig. 2 systematically shifts toward higher values with increasing the heating rate. This confirms that the process responsible for the occurrence of these anomalies (retrification) is an thermally activated process.

Measurements of the temperature dependencies of EEE intensity at four different heating rates (2, 5, 10 and 20 K/min), and the DTA curves at five heating rates (1, 2, 5, 10 and 20 K/min) enabled the determination of the activation energy for the retrification

process at the surface and in the volume of the samples, responsible for the occurrence of the maxima on the EEE and DTA curves, correspondingly. Activation energy was determined using the well-known Ozawa relation [12]:

ln v = A--

kT

where v is the heating rate, A - constant, E - activation energy, k - Boltzmann's constant and T - transformation temperature.

The retrification temperature T has been determined from the position of the maximum on the EEE curves [13], and as the deflection point (from the base line) on the DTA curves [14].

Activation energy of the retrification process is a parameter characterizing well the thermal stability of amorphous materials. The values of the activation energy for the retrification process in the surface layer and in the volume of non-irradiated and y-irradiated chalcogenide glass AsxSei0o-x, determined in the present study on the basis of systematic EEE and DTA investigations by the Ozawa method, are collected in table 1. For both the non-irradiated and y-irradiated AsxSe100-x samples the activation energy for the surface retrification is smaller than that for volume retrification. Thermal stability of the y-irradiated samples is greater than that of the non-irradiated material (activation energy for retrification process in irradiated samples is greater than that for non-irradiated material).

Table 1

Activation energies for the volume and surface retrification of investigated AsxSe100-x chalcogenide glasses as determined from the DTA and EEE measurements, respectively

As content, x, type of sample

Activation energy in eV

 

Surface retrification

Volume retrification

10 - a

0,75

1,91

10 - b

0,83

1,99

20 - a

1,10

1,61

20 - b

1,21

1,74

30 - a

1,28

1,62

30 - b

1,40

-

From the results of the present study it follows out that:

- retrification processes in the surface layer occurs with an activation energy smaller than that in the volume,

- y-irradiation causes an increase in the value of the activation energy for retrification process in both the surface layer and in the volume, thus enhancing the thermal stability of chalcogenide glasses AsxSe100-x (see also [5]),

- the combination of the EEE and DTA methods would be very useful and efficient in investigations of the crystallization kinetics and thermal stability of chalcogenide glasses.

Further studies are in progress.

1. Saiter J.M. Physical ageing in chalcogenide glass // J. Optoelect. Adv. Mat. 2001. Vol. 3. P. 685-694.

2. Ohta T., Birukawa M., Yamada N., Hirao K. Optical phase change and magneto-optical recording // J. Magn. and Magn. Mat. 2002. Vol. 242-245. P. 108-115.

3. Galemczuk R., Bonjour E. Gamma-ray induced relaxation in selenium glass // J. Non-Cryst. Solids. 1981. Vol. 43. P. 427-432.

4. Golovchak R., Gorecki Cz., Kozdras A., Shpotyuk O. Physical ageing effects in vitreous arsenic selenides // J. Solid State Commun. 2006. Vol. 137. P. 67-69.

5. Golovchak R., Shpotyuk O., Shpotyuk M. et al Ageing effects in As10Se90 chalcogenide glasses induced by y-irradiation // Ukr. J. Phys. 2005. Vol. 50. P. 690­693.

6. Wagner T., Kasap S.O., Petkow K. Temperature-modulated differential scanning calorimetry studies of the structure of bulk and thin film GexAsyS60 chalcogenide glasses // J. Mat. Sci. 1997. Vol. 32. P. 5889-5893.

7. Gorecki Cz., Gorecki T., Michno Z., Thermal stability of the Fe40-xNi40CrxB20 metallic glasses as studied by the EEE and DTA methods // Acta Phys. Polon. 1987. Vol. A72. P. 157-160, Thermal stability of the Ni78SixB22-x metallic glasses as studied by the EEE and DTA methods // Acta Phys. Polon. 1987. Vol. A72. P. 161­163.

8. Gorecki Cz., Gorecki T., Golovchak R. et al. Kinetics of phase transitions in semiconducting amorphous chalcogenides AsxSe100-x as studied by differential thermal analysis and exoelectron emission techniques // Visnyk Lviv. Univ. 2005.

Vol. 38. P. 399-403.

9. Gorecki Cz., Gorecki T., Kozdras A., Golovchak R. Kinetics of phase transitions in vitreous chalcogenide semiconductors AsxSe100-x as studied by differential thermal analysis (DTA) and exoelectron emission (EEE) methods // Visnyk Lviv. Univ.

2007. Vol. 40. P. 254-260.

10. Gorecki Cz., Gorecki T. Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique // J. Phys. Conf. Ser. 2007. Vol. 79. P. 1-5.

11. Gorecki Cz., Gorecki T., Szymura S. Surface and volume crystallization of metallic glass (Ni50Zr50)999P01 as investigated by exoelectron emission (EEE) and differential thermal analysis (DTA) // Modern Phys. Lett. 2002, Vol. 16. P. 87-92.

12. Ozawa T. Kinetics of non-isothermal crystallization of amorphous materials // J. Thermal Anal. 1970. Vol. 2. P. 301-312.

13. Sujak B., Gorecki T. Egzoemisja elektronow podczas przemian fazowych i reakcji w cialach stalych // Wiadomosci Chemiczne. 1973. Vol. 37. P. 361-384.

14. Schultze D. Termiczna Analiza Roznicowa (Differentialthermoanalyse). Warszawa,

PWN, 1974.

15. Golovchak R.Ya., Kozdras A., Shpotyuk O.J.Physical ageing in vitreous As13,5Ge4,5Se82 modified by high-energy gamma-irradiation // Phys. B. 2006.

Vol. 371. P. 323-326.

16. Golovchak R.Ya., Kozdras A., Gorecki Cz., Shpotyuk O.J. Gamma-irradiation-induced physical ageing in As-Se glasses // J. Non-Cryst. Solids. 2006. Vol. 352.

P. 4960-4963.

ТЕРМІЧНА СТАБІЛЬНІСТЬ ТА КІНЕТИКА СТРУКТУРНИХ ПЕРЕТВОРЕНЬ СКЛОПОДІБНИХ ХАЛЬКОГЕНІДНИХ НАПІВПРОВІДНИКІВ СИСТЕМИ AsxSe100-x

Ч. Турецький1, Т. Турецький2, М. Костжева1

1 Фізичний факультет, Технічний університет Ополє вул. Озімска 75, 45-370 Ополє, Республіка Польща

2Інститут фізики, Університет Ополє, вул. Олеска 48, 45-052 Ополє, Республіка Польща

Досліджено кінетику фазових переходів в y-опромінених і неопромінених халькогенідних стеклах As^e^o* (х = 10, 20 і 30) методом диференціального термічного аналізу та технікою ексоелектронної емісії. Енергії активації досліджених матеріалів визначались методом Озава. З'ясовано, що енергія активації у поверхневому шарі менша, ніж в об'ємі. Показано, що у-опромінення поліпшує термостабільності досліджуваних матеріалів.

Ключові слова: халькогенідні стекла, ДТА, екзоелектронна емісія, енергія активації, у-опромінення.

ТЕРМИЧЕСКАЯ СТАБИЛЬНОСТЬ И КИНЕТИКА СТРУКТУРНЫХ ПРЕВРАЩЕНИЙ СТЕКЛООБРАЗНЫХ ХАЛЬКОГЕНИДНЫХ ПОЛУПРОВОДНИКОВ СИСТЕМЫ AsxSe100-x

Ч. Гурецкий1, Т. Гурецкий2, М. Костжева1

1 Физический факультет, Технический университет Ополе ул. Озимска 75, 45-370 Ополе, Республика Польша

2Институт физики, Университет Ополе, ул. Олеска 48, 45-052 Ополе, Республика Польша

Исследована кинетика фазовых переходов в у-облученных и необлученных халькогенидных стеклах AsxSe100-!C = 10, 20 и 30) методом дифференциального термического анализа и техники экзоэлектронной эмиссии. Энергии активации исследованных материалов определялись методом Озава. Установлено, что энергия активации в поверхностном слое меньше, чем в объеме. Показано, что у-облучение улучшает термостабильность исследуемых материалов.

Ключевые слова: халькогенидные стекла, ДТА, экзоэлектронная эмиссия, энергия активации, у-облучение.

Стаття надійшла до редколегії 04.06.2008 Прийнята до друку 25.03.2009

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Cz Gorecki, T Gorecki, M Kostrzewa - Thermal stability and kinetics of structural transformations in vitreous chalcogenide semiconductors