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28Journal of Siberian Federal University. Engineering & Technologies 6 (2013 6) 650-656
УДК 666.3
Characteristic Physical-Mechanical and High-Temperature Electric Properties Semicinductor Ceramic Based SnO2 with Addition MnO2 and CuO
Sergey S. Dobrosmyslov*, Vladimir I. Kirko, Gennady E. Nagibin, Oksana A. Resinkina and Zahar I. Popov
Siberian Federal University 79 Svobodny, Krasnoyarsk, 660041 Russia
Received 05.07.2013, received in revised form 02.09.2013, accepted 10.09.2013
Ceramic semiconductor SnO2-based materials with MnO2 and CuO additives were synthesized at 1300 °C and 1400 °C There has been carried out an investigation of the physical-mechanical and high-temperature electric properties. As a result, sintering of the material with MnO2 additive is shown to be improved at increasing firing temperature. The composition 96 % SnO2-2 % Sb2O3-2 % CuO made at the temperature 1300 °C has the best electrophysical properties (its resistivity is 0.09 mOhm m). The resistivity of the 94 % SnO2-2 % Sb2O3-2 % CuO-2 % MnO2 composition in the high-temperature region is more by a factor of 3. The 96 % SnO2-2 % Sb2O3-2 % MnO2 composition has nonlinear voltage-currant characteristic, and hysteresis is present.
Keywords: ceramic, tin oxide, conductivity, currant - voltage characteristic.
Introduction
The tin dioxide based ceramics is being used in many branches of industry - electronics, electrical engineering, electrochemistry, catalysis, biotechnology, metallurgy, atomic and chemical industries, etc. [1]. SnO2 is an n-type semiconductor having the band-gap energy 3.54 eV, whose properties basically depend on its microstructure and synthesis method. The wide range of use imposes special requirements on the material properties and thus on the synthesis method.
High-porous polycrystalline materials having a large amount of structural defects are used as catalysts and semiconductor gas sensors [2-6]. Oxygen vacancies forming in the surface active layers of the tin dioxide pores are the areas of the physical or chemical adsorption the presence of which is necessary for the gas sensing ability. On the other hand, high-density SnO2-based ceramics due to its high electro conductivity at high temperatures is used as the high temperature-electrodes [7], for instance, in the aluminum electrolysis and glass making [8]. Without glass-forming additives tin dioxide possesses a low value of sinterability which is caused by the domination of vaporization and
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* Corresponding author E-mail address: dobrosmislov.s.s@gmail.com
condensation processes over diffusion ones [9] because SnO2 starts evaporating from the temperature 1100°C And this limits the material densification.
One of the ways to increase the ceramic material sinterability is the addition of fine-grained oxide materials such as ZnO [10], CuO [11], MnO2 [12, 13], CoO [14], FeA [13], and to improve electrical properties V2O5 [6] and Sb2O3 [15] are added. The addition of 1 mol. % CuO is especially effective because of the liquid phase formation. The Cu-O eutectic is 1080°C [16]. A significant improvement of the electrophysical properties is provided with the Sb2O3 addition.
The aim of the paper being presented is the investigation of physical-mechanical and high-temperature electrophysical properties of a ceramics based on 96 %SnO2-2 %Sb2O3-2 %CuO with superdispersed MnO2.
Experimental technique
The specimens were made with the conventional ceramic technology. The initial SnO2 powder charge was prepared in the aqueous solution of Mn and Cu salts. And then it was preliminarily subjected to a thermal treatment at 1100 °C followed by grinding. Then the charge was formed into a specimen using the 5 % polyvinyl alcohol solution as a binder. The specimen burning was carried out at 1300 °C and 1400 °C for 2 h. For the physical chemical tests the ceramic specimens were made in the form of cylinders 15 mm in diameter and 10 mm high, respectively. For the electro physical measurements the specimens of a rectangular shape 5*4* 50 mm were taken. The specimen's density was measured with the hydrostatic weighing method in alcohol and the open porosity according to the State Standard 2408-95. The resistivity was measured with the four-point probe method in the temperature range 20-1000 °C [17]. The mechanical properties were measured with the device Instron 3369. The crystalline structure of the ceramics was identified with the X-ray analysis in XRD 6000. The surface fracture pictures were taken with the scanning electron microscope (SEM) JEOL JSM-7001F (Japan).
Experimental results and discussion
In Table 1 there are presented the results of the physical-mechanical properties investigation of the ceramics and its resistivity values at T = 1000 °C.
The experiment number is in the first column. The charge composition and final firing temperature are presented in the second and third ones, respectively. The measured values of density, open porosity, mechanical strength and resistivity are presented in columns 4 to 7.
As follows from the table a complete change of CuO for MnO2 leads to the mechanical and electrical properties degradation (experiments 1 and 2). The firing temperature increase leads to increased density and strength and decreased open porosity (№ 23 and № 45). The best composition of the investigated ones is 94 % SnO2-2 % Sb2O3-2 % CuO-2 % MnO2. This ceramics has the best physical-mechanical properties (№ 7).
The measurement results for the ceramics strength at uniaxial compression obtained with Instron 3369 are presented in Fig. 1.
As can be seen from the figure the ceramics ultimate strength decreases with increasing MnO2 concentration. The Young's modulus is practically unchanged. A little addition of the glass-forming CuO phase leads to a significant ultimate strength increase and change of the deformation behavior and
Table 1. Physical-mechanical properties and resistivity of the ceramics under investigation
№ Charge composition Firing temperature, °C Density, g/cm3 Open porosity, % Strength, MPa Resistivity, mOhm*m 7= 2000 °C
1 2 3 4 5 6 7
1 96 % SnC>2-2 % Sb2Ü3-2 % CuO 1300 5.4 10.9 255.3 0.09
2 96 % SnO2-2 % Sb2O3-2 % MnO2 1300 5.5 10.5 91.2 0.80
3 96 % SnO2-2 % Sb2O3-2 % MnO2 1400 6.1 6.1 158.2 -
4 94 % SnO2-2 % Sb2O3-4 % MnO2 130S 9.5 17.2 1 32.5 0.80
5 94 % SnO2-2 % Sb2O3-4 % MnO» 1400 6.1 5.1 257.6 -
6 90 % SnO2-2 % Sb2O3-8 % MnO2 1300 5.3 18.6 149.7 0.99
7 94 % SnO2-2 % Sb2O3-2 % CuO-2 % MnO2 1300 6.(5 0.11 424.8 1.7
0,0 0.1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7
Comression deformation (%)
Specimen
1 -M%SnO,-2%SbA-2%MnO:
2 - 94%SnO,-2%Sb:Os-4%MnO,
92%Sn0:-2%Sb:03-e%Mii0:
-95%Sii0:-l%Sb:03-2%Cu0-2%Mii0.
- 94%Sii0;-2%Sb:03-2%Cu0-2%Mii0:
T (firing) =1300 °C
Fig. 1. Dependence of the ceramics strength on the degree of their compression deformation
fracture pattern (from brittle to visco-brittle). On the curves in a number of cases an abrupt material destruction takes place that serves as evide nc e of deformation behavior change.
The pictures of fhe ceramic specimen's suifsce fracture are presented in Fig. 2. The fracture structure also witnesses the change of the fracture pattern from brittle (a) to visco-brittle (b).
As can tie ieen from the pictures in Fig. 2 in tic hioxide wiih CuO or MnOc additives there are formed pores whose size is 20 ^m in case of 2 % CuO addition (Fig. 2 (1)). In ceramics with CuO and MnO2 the large pores are practically absent as well as the pores of a less size.
Pkfures of the ceramics fracture;. at 5000-fold magnification are presented in Fig. 3.
The Fig. 3 shows that the destruction of the specimen 96 % SnO2-2 % Sb2O3-2 % CuO occurs through particle bodies, but that of the specimen with 2 % CuO and 2 % MnO2 additives along the grain boundaries. It seems to take place through the glass-forming phase CuMn2O4, CuL5MnL5O4 [18].
It is known that when MnO2 is added into polycrystalline tin dioxide, Mn2SnO4 forms on the grains' surfaces, which interferes with a good material sintering [19]. This does explain a high porosity of the material and its low strength. In case of MnO2 - CuO additive combination there takes place the
(a) (b)
Fig. 2. Pictures of the materials under investigation obtained with SEM JEOL JSM-7001F, x500; 1 - poaes: (a) 96 % SnO2-2 % SbA-2 % CuO; (b) 94 % SnO2-2 % Si'b^C-1-2 % CuO-2 °ii. MiUC
formation of CuMnOx-phase tbasically, CuMn2O4, ^u15]VIn19(((4() i19]) thnt is a glass-forming one on the grains ' b oundaries i^tnd promoted sinleri ng.
To improve the electrophysical properties Sb2O3 way used. Duding the high-temperature sintering in the polycrystalline SnO2 lattice tlieris takes polaic-e a substitution of the tetravaleot tin atoms by pentavale nt ontimony ones [220] thdt peov ides the p-type conducitvite and snbstantially decreases tide energy-gapwidt". The c eramics receptivity measurement results ve reus tnmpe ratuee are presented in F(g. 4.
It has been mentioned above that Sb2O3 is used as an additive improving the material's electrical conductivity. In the compositions of Fig. 4 tine Sb2O3 concentration (the number o° tlie electrical charge carriers) 9s constant. The lesistivity depend. on the electrical contact between the sinlered particles. The materia( witlt the CuO additive has tloe; lowest resistivity (0.9 mOhm nt, Tdble 1, №1). The Table 1 and Fig. 4 show that when MnO2 is used, the resistivity is independent of this phase concentration. It is possible to explain this fact by no influence of Mn2SnO4 on the electrical contact between the sintered SnO2 particles. The voltage-current characteristics of the specimens are presented in Fig. 5.
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Fig. 4. T-dependencies ofthe re;ssistivity of SnO2-based materials with different additions
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Fig. 5. The specimens' voltage-current characteristics obtained in 3! measurements (T = 1000 °C): 1 - increasing current; 2 - decreasing current, a) 96 % SnO2-2 % Sb2O3 -2 % CuO t) 96 % SnO2-2 % Sb2O3-2 % MnO2
■ ■
■
The curves show a dependence on the material's phase composition. In case of the 96 % SnO2-2 % Sb2O3-2 % CuO composition the voltrge-current cCaracteristics ¡are licear which serves as? an e-idence of the resistivity being constant at current load increasing (a). In conteast to thie, in specimens having CuO substituted by iupeedispersed MnOt the resistivity decreases practicaMly by a factor of 2 with the rucrent load innreasing from 1 ^o 1(S (b). Tire latter can be assoc iated either with a generation of extra charge carriers on the interphase boundaries od the p-rticles, oe with the hegirniing of a flow along the boundaries because of the heat generation increased. Moreover, in case of the material with superdispersed MnO2 voltage-current characteristic shows hysteresis (Fig.1 b) that can be explained with a later no oling of the Sn02 particles compaeed to that of the intnephase bou ndaries when decreasing the cuerent load.
Conclusions
1. The specimens of the 96 % SnO2-2 % Sb2O3-2 % CuO composition sintered at 1300 °С have the best electrophysical characteristics;
2. The substitution of CuO by MnO2 leads to the degradation of the material's mechanical properties;
3. The use of the superdispersed MnO2 - CuO additive combination leads to a substantial increase of the mechanical strength and change of the fracture mechanism from brittle to visco-brittle;
4. In the compositions with MnO2 - CuO additives there has been revealed a nonlinearity of the voltage-current characteristic. When the current load increases, the resistivity decreases. Moreover, there is revealed a hysteresis of the voltage-current characteristic.
Article was supported by RFBR № 12-03-31323
Статья выполнена при поддержке РФФИ № 12-03-31323
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Особенности физико-механических и высокотемпературных электрофизических свойств керамических полупроводниковых материалов на основе SnO2 c добавками MnO2 и CuO
С.С. Добросмыслов, В.И. Кирко, Г.Е. Нагибин, О.А. Резинкина, З.И. Попов
Сибирский федеральный университет Россия 660041, Красноярск, пр. Свободный, 79
Синтезированы керамические полупроводниковые материалы на основе диоксида олова с добавками MnO2 и CuO. Температуры синтеза были 1300 и 1400 °С. Проведены исследования физико-механических и электрофизических свойств. Показано, при повышении температуры обжига для материала, полученного при использовании MnO2, происходит существенное улучшение спекания. Наилучшими электрофизическими характеристиками обладают образцы состава 96%SnO2-2%Sb2O3-2%CuO полученные при температуре обжига 1300 °С(УЭС 0,09 мОм*м). УЭС состава 94%SnO2-2%Sb2O3-2%CuO-2%MnO2 в высокотемпературной области выше в 3раза. Для состава 96%SnO2-2%Sb2O3-2%MnO2 вольтамперная характеристика имеет нелинейный вид и присутствует гистерезис.
Ключевые слова: керамика, диоксид олова, электропроводность, вольтамперная характеристика.
