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CHEMICAL PROBLEMS 2019 no. 3 (17) ISSN 2221-8688 429
UDC 546.87.546.289.546.31
PHYSICAL AND CHEMICAL RESEARCH INTO (2Bi2O3B2O3)100-x - (2 Bi2O33GeO2)x SYSTEM AND ELECTROPHYSICAL PROPERTIES OF OBTAINED ALLOYS
S.I. Bananyarli, R.N. Gasimova, Sh.S. Ismayilov, L.A. Khalilova
Institute of Catalysis and Inorganic Chemistry of the National Academy of Sciences of Azerbaijan 113, H. Javid ave., AZ1143, Baku; e-mail: ishr_az.yahoo.com
Received 13.07.2019
Abstract: The paper presents the results of studies into physical-chemical and electrophysical properties of alloys of the (2Bi2O3 B2O3)100-x - (2 Bi2O3 3GeO2)x system. Frequency dependences of electrical impedance (R), dielectric permittivity (s') and dielectric losses (tg a) in alternating current and different temperatures were studied. It found that in samples the conductivity is mainly hopping conductivity with lengths varied between localized states.
Keywords: conductivity, frequency dependence, composition, frequency, chemical analysis, temperature. DOI: 10.32737/2221-8688-2019-3-429-434
Introduction
Numerous applications of oxide materials including Bi2O3, B2O3, GeO2 (SiO2) and their alloys are related to characteristics of their properties [1-4]. Owing to optical transparency of dispersion of refractive index, chemical resistance and mechanical density, they can be used for preparation of various devices and microcircuits in electronics and microelectronics as scintillation materials in nuclear physics [56]. The need in bismuth-borate oxides makes it necessary to conduct a systematic study of the oxide materials. There are many works on the study of state diagram of the Bi2O3 - B2O3 system. For example, when analyzing the state diagram of the Bi2O3 - B2O3 system, authors of the research indicate the existence of 5 compounds (12: 1), (2:1), (3 :5), (1: 3) and ( 1 :4) which are in metastable state in the Bi2O3 -GeO2 [7] system.
Authors [8] studied the Bi2O3 - GeO2 system as regards compositions containing up to 22 mo^% GeO2. In addition, a stable state diagram of the Bi2O3 - B2O3 system has a phase separation area. In the works [4, 9] in specified concentration ranges we observed a wide region
of solid solutions in the metastable state based on a high-temperature modification. They state that besides o-Bi2O3 phase the system also contains stable phases Bii2GeO2o of selenite structure and Bi4(GeO4)3 evlitine struture resulted in partial decay of the metastable solid solution.
Authors [10-11] researched a ternary system Bi2O3-B2O3-SiO2 and analyzed electrophysical properties of obtained samples. In this system, the type of alloys conductivity with semiconducting properties was identified. At T=300-500K the values of dielectric permittivity and losses change in line with ranges of s"=20-60; tgô=0.02-0.06 and are relatively stable. Depending on the composition, the resistance changes into p> 106-101f Om •cm to establish that some compositions of the system (2Bi2O3-3SiO2)100-x~(2Bi2O3-B2O3)x has practical value [12]. As is known, depending on the ratio of components in the + x Si02
system many compositions of the alloys characterized by physical-chemical and physical properties were obtained [5, 14]. Study into properties of an alloy in the (2Bi2O3-B2O3)100-x -
(2Bi2Or3GeO2)x composition is of great interest [13].
Eariler we have conducted differential-thermal and X-ray analyses of alloys in the 2Bi2O3-B2O3-2Bi2O3-3GeO2 composition and temperature dependence of conductivity (o), thermal conductivity (x) and dielectric permittivity in the direct current. It is expected that the alloys in the (2Bi2O3 •B2O3)1oo-x -(2Bi2O3-3GeO2) x, system have disordered cluster centers, so their composition grows as the concentration of B2O3 increases at high temperature (T= 460-480 K) where loosening
and blurring of phase transition occur [13].
To obtain the precise and reliable results for high-impedance oxide materials, an analysis into electrophysical parameters in the direct current is insufficient: these paraemters must also be measured in the direct current. Aim of this work is a physical-chemical research into the 2Bi2O3-B2O3 -2Bi2O3-3GeO2 system and an analysis of frequency changes of conductivity (p), dielectric permittivity (s') and losses ( tgo) in the direct current to thus identify the conductivity mechanism and provide general characteristics of the properties of these systems.
Experimental part
Alloys of the (2Bi2O3 •B2O3)ioo-x - (2 Bi2O3 •3GeO2)x system were synthesized from Bi2O3 oxides of chemically pure GeO2 - high purity and H3BO3 - analytical reagent grade in the furnace SNOL at 1273-1373K. Alloys were cast at a room temperature on a titanium plate. All samples were glassy from light brown to brock brown. Glasses were annealed at 673 K for 200 hours.
Note that objects of study were samples of the compositions: N1 x= 10 mol% (2Bi2O3 -3GeO2); N2 x=15mol% (2Bi2O3-3GeO2) and N3 x= 50 mol%(2Bi2O3 -3GeO2). Interaction in the system (2Bi2O3 - B2O3)1oo-x - (2Bi2O3 -3GeO2)x was studied using the methods of differential-thermal, X-ray ohase analyses, as well as the
measurement of density of compositions. DTA of system alloys was studied by derivatograph NETZSCH.STA 449 F3, STA 449F3A - 0,836 -M.
Also, X-ray phase analysis was conducted by diffractometer D2 Phaser Bruker.
Density of alloys was determined by hydrostatic weighing where distilled water was used as operating fluid.
Conductivity (g) and dielectric permittivity s' and dielectric losses tgG were studied at different frequencies in the alternating current at 300, 385 and 430K.
Thickness of samples were d=2-4 mm; width - b=8mm and length l=14mm
Results and discussion
Fig. 1 shows the results of DTA for the sample N1.
-94,06— -SO—
I -00 —
[
I -40-
\ -20 — i
0 —
20 — 413 — 60 — 77.97 ~
200 — 209
Temperature (°C)
Fig.1. Results of DTA for the sample N1 - 10 mol% 2Bi2O3-3GeO2
As can be seen from the figure 1, at T1 = 340 ° C a weak endothermic peak is observed, i.e. weak association occurs (with the covalent bond being fixed). At T2 - (450-460)°C, an
exothermic reaction occurs with a transition and with an increase in covalent bond. At temperatures T3~470°C, T4~590°C and T5~650°C, endothermic effects are observed.
Frequency dependences of electrical impedance (R), dielectric permittivity (s') and dielectric losses tgo were studied in samples of the (2Bi2O3 -B2O3)100-x - (2Bi2O3 -3GeO2)x system with the following compositions: N1 x=10; N2 x=15; N 3-x=50 mol% 2Bi2O3 •3GeO2. Fig. 2 shows the results of frequency
V (Hz)
Fig.2. Frequency dependences of conductivity in the sample N1- 10 mol% (2Bi2O3-3GeO2)
Similar measurements were conducted with the sample N3 (Fig.3, N3- 50mol% (2Bi2O3 •3GeO2). According to Fig. 3, dependence R-1(u) substantially differs from values of sample N1 (Fig. 2). At lower frequencies, u< 103Hz conductivity changes by the law R-1~u04 if higher than u >103 Hz. Also,
strong growth of conductivity from frequency
-1 2.0
R ~u ' is observed where values of conductivity correspond to our values obtained in the constant current [ 13 ] (Fig. 2. circuit 3). At high temperatures up to (T= 385K) the frequency dependence of conductivity in the
dependence of conductivity in the sample N1 (10mol% 2Bi2O3 -3GeO2). According to Fig. 2, at T=300K the change of R-1(u) in the frequency range (from 10-1 to105 Hz) occurs by the law R-1 ~ u05 with the gorwth of u in relatively low frequencies. With higher
35
frequencies in the frequency range of 10 <u<10
1 0 8
the conductivity changes by the law R- ~u . , i.e. the conductivity grows exponentially with the increase of frequency of oscillating electrical field. At high temperatures (T=380K), frequency dependences of conductivity are weakened (Fig. 2, 3) and conductivity changes by the law R-1~ u03 at u > 103Hz.
1 _
11/ 11f 14' I -Tl* ]U Itf
v (HzJ|
Fig.3. Frequency dependences of conductivity of the sample N3- 50mol% (2Bi2O33GeO2)
alternating current weakens and changes in line with the law R-1~u 06. Note that weak exponential growth remains to quantitatively differ from measured ones in the constant current [13]. Measurements of conductivity higher than T>400K show that in frequency range of u< 105 Hz conductivity remains practically constant (R-1~ const) (Fig.3 curve 3 T=430K). Apparently, the conductivity mechanism is effective due to the transition of carriers of excited, yet in non-localized state close to the valence-band edge [14]. Apparently, the mechanism of conduction is due
to the transfer of carriers of excited but nonlocalized states near the valence band [14].
In these samples (samples N2, N3), the frequency dependences of dielectric permittivity s'(u) and dielectric losses in the sample N3 were measured. The results are given in Fig. 4. According to samples N2 s'(u)~u-068 N3 s'(u)~u-104, depending on frequency the dielectric
permittivity s'(u) sharply falls in the frequency
1 2
region 10" <u<10 Hz; however, subsequent rise in frequency to 105Hz it weakens and decreases.
None that sharp decrease at low frequencies (from 10-1 to 102 Hz), by the law s'(u)~u-144 is possibly due to additional migration mechanism of polarization in the macroscopic nonhomogeneous structure and mixtures. This migration polarization occurs in lower frequencies due to considerable electric energy dissipation. Occurrence of this polarization is explained as being due to cluster centers with different conductivity.
Fig.4. Frequency dependence of dielectric permittivity of samples N2 and 3 and dielectric losses (tg a) of the sample N3, T=300K
Fig. 4 shows frequency dependence of dielectric loss in the sample N3. Dielectric loss (tga) in low frequencies sharply falls to u<102 Hz with a value of tga~2.3. In the course of further increase of frequency up to 105 Hz, it remains constant.
Thus, the study of samples at alternating current and a wide frequency range at room temperature confirms our assumption [13] that the studied compositions contain disordered cluster centers and their content increases with increasing Bi2O3 concentration. With increasing temperature, loosening occurs and a phase transition is observed at T ^ 460 K. However,
research into alternating current in the wide range of frequency showed that during destruction of cluster centers the migration polarization related to non-homogeneity of the structure occurs in alloys besides dipole -relaxati on p ol ari zati on . Note that the mi gration polarization is observed at low frequencies 10-1< u <10 Hz (Fig.4.) by partial hopping conductivity with different wavelengths between chaotic distributed cluster centers. With increase of field frequencies, the dipole-relaxation polarization by migration polarization that arises in dissociation of cluster centers has a dominant role [13].
Conclusion
1) Conductivity mechanism in the (2Bi2O3-B2O3)100-x - (2 Bi2O3-3GeO2)x system occurs due to non-localized excited carriers close to valence-band edge. At high temperatures the conductivity intensifies due to disorder in cluster centers.
2) Samples contain cluster centers and their number increases with growth of Bi2O3 concentration. Softening occurs at high
temperatures but at T^460K gentle slopes of phase transitions are observed. 3) It is expected that during the decomposition of cluster centers in alloys the dipole-relaxation polarization is formed and the migration polarization which is related to non-homogeneity of bulk structures appears additionally.
References
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(2Bi2ÜrB2O3)ioo-x (2Bi2O3 3GeO2)x SiSTEMiNiNFiZM-KiMYÖVi TßDQiQi Vß ALINAN ßRiNTiLßRiNELEKTROFiZiKiXASSßLßRINiN ÖYRßNiLMßSi
S.i. Bananyarli, R.N. Qasimova, §.S. Ismayilov, L.3. Xalilova
AMEA akademikM.Nagiyev adina Kataliz va Qeyri-üzvi Kimya institutu AZ1143 Baki, H.Cavidpr.113; e-mail: ishr_az.yahoo.com
Bu maqalada (2Bi2O3B2O3)100-x - (2 Bi2O33GeO2)x sistemi arintilarinin fiziki -kimyavi va elektrofiziki xassdhrinin tadqiqinin naticalari verilmi^dir. Dayi^an carayanda va müxtalif temperaturlarda elektromüqavimatin (R), dielektrik nüfuzlugun (s') va dielektrik itkinin (tg a) tezlik asililiqlari öyrsnümi^dirMüsyysn edilmi^dir ki, tadqiq etdiyimiz nümunalarin elektrik kegiriciliyi mexanizmi asasan saviyyalar arasi sigrayi^li kegid hesabina ba§ verir.
Agar sözlar: elektrokegiricilik, tezlik asililigi, tarkib, tezlik, kimyavi analiz, temperatur.
ФИЗИКО- ХИМИЧЕСКОЕ ИССЛЕДОВАНИЕ СИСТЕМЫ (2Bi2OrB2O3)ioo-x (2Bi2Or3GeO2)x И ИЗУЧЕНИЕ ЭЛЕКТРОФИЗИЧЕСКИХ СВОЙСТВ ПОЛУЧЕННЫХ СПЛАВОВ
С.И. Бананярлы, Р.Н. Касумова, Ш.С. Исмайлов, Л.А. Халилова
Институт Катализа и Неорганической Химии им. акад. М. Нагиева Национальной АН Азербайджана AZ1143 Баку, пр.Г. Джавида,113; e-mail: ishr_az.yahoo.com
В статье представлены результаты исследования физико-химических и
электрофизических свойств сплавов системы (2Bi2O3B2O3)100-x - (2 Bi2O33GeO2)x. Изучены частотные зависимости электросопротивления (R), диэлектрической проницаемости (е') и диэлектрической потери ( tg а) при переменном токе и различных температурах. Выявлено, что в исследуемых образцах проводимость является в основном прыжковой проводимостью, но с различной длиной между локализованными состояниями.
Ключевые слова: электропроводность, частотная зависимость, состав, частота, химический анализ, температура.
