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CORRELATION OF STRUCTURAL PARAMETERS WITH COBALT, BORON, BISMUTH AND CHROMIUM OXIDES WITH NON-OHMIC ELECTRICAL
CONDUCTIVITY
YUSIBOVA TARANA FIRGET
PhD in physics and mathematics, docent, Head of the Department of Physics and Ecology, Mingachevir State University, Azerbaijan,
Mingachevir city
Abstract. This article is dedicated to the study of the electrical properties of varistors synthesized on the basis of zinc oxide with CoO, Bi2O3, MnO2 , Sb2 O3 additives, as well as to clarify the relationship between them and structural parameters by electrographic methods. ZnO with bismuth, cobalt, boron, etc. additives is used in the preparation of varistors, which are used as overvoltage limiters and have non-linear VAX. In this case, the electrical properties of varistors strongly depend not only on the amount of additives included in it, but also on the synthesis mode. Examples, 97.5ZnO, 0.5Bi2O3, 0.5CoO, 0.5MnO, 1.0Sb2O3 mol%. The synthesis of ceramics was carried out under air conditions for one hour. Ceramic synthesis temperature was 900-15000C. The dimensions of the samples were equal to 6x6x1 mm3. Al measuring electrodes were obtained by means of thermal evaporation in vacuum. The dielectric constant of the samples was determined at T=293K using an E-20 immittance measuring device. Measurements were made at the frequency f=1kHs. Particle sizes were determined in a MIM-7 microscope. At the same time, the conductivity of ceramics increases in the part of VAX corresponding to Ohm's law. The dielectric constant of ceramics increases as the particle size of ceramics increases [1-27].
Keywords. Zinc oxide with CoO, Bi2O3, MnO2, Sb2O3 additives, nonlinear VAX, dependences of I=f(U), lgo=f(1/T) and lga=f(E,T), ceramics, varistor, cobalt, boron, bismuth and chromium oxides, non-ohmic electrical conductivity, MIM-7 microscope, line radiographs, Interphase layer.
The methodology of the experiment and their analysis. Research samples (varistors) were synthesized at temperature t=13000C. The thickness of the varistors is 4.7 mm and the diameter is 28 mm. Dependencies I=f(U), lg a=f(1/T) and lg a=f(E,T) are set in varistors: In Figure 1, I=f(U), lg a=f(1/T) and lg a=f(E,T) dependences are given, from which the following properties are determined. VAX is non-linear in the entire temperature range. With the increase in temperature, I=f(U) curves shift to the area of small values of the electric voltage, and the value of the current passing through the sample increases by approximately 3 orders (Fig. 1). The dependence of electrical conductivity (a) on temperature and voltage is exponential (Fig.2). 3-4 characteristic areas are observed in the lg a=f(1/T) curves (a,b,c,d) [14-20].
Figure 1. Varistor volt-ampere characteristics at different temperatures.
Figure 2. Dependence of electrical conductivity on temperature at different voltages [19-20].
Figure 3. Dependence of electrical conductivity on voltage at different temperatures [19-20].
Based on the above, the obtained experimental results can be explained as follows. To obtain a homogeneous layer, the NaCl and KCl bases were previously degassed in a vacuum at 250 0C for 2 hours. Deposition of the layer on the substrate occurs at room temperature. The thickness of the layer is 30 nm, and the deposition rate is equal to ~ 5 nm/sec. The first two reflexes observed in the electrogram, a=0.4389 nm; c=0.2862 nm, PQS corresponds to MnO2 phases with tetragonal lattice parameter P4/nm. Also in this electronogram, the lines of a-CoO chemical compounds with cubic syngonium a=0.4256 nm are also given. The interfacial distance, which does not belong to B2O3 or Bi2O3 chemical compounds, was also recorded as a single value in the diffraction pictures . It should be noted that in the end a=0.5834nm, b=0.814nm; c=0.748 nm, slightly different from Pmonoclinic B2O3 with =670 07'. Because of the difference between the available intensities of the corresponding reflections of B2O3 and Bi2O3 , and since the effective ionic radius of Bi (0.110 nm) is approximately larger than the effective ionic radius of B (0.110 nm), the effect of scattering ability (Bi2O3 ) is stronger here which suggests that they belong to the Bi2O3 additive. In the use of thin films, this can occur due to the reaction of metals with other oxygen-containing elemental pairs with comparable melting temperatures and complex molecular structure of the crystal lattice. As a result, thin-layered polycrystalline Zn1-x SbxO is more stable, they do not undergo both natural and artificial aging in the temperature range indicated in the work, according to structural changes-phase transformations [1522]. For this purpose, during the preparation of varistors, Bi2O3 was replaced by glass containing lead oxide. Therefore, the study of non-ohmic ceramics with lead oxide addition compared to bismuth oxide can give more interesting results. Ceramics with both PbO and Bi2O3 additions previously, as well as PbO+Bi2O3+ZnO glass addition after grinding. Bi2O3 added ceramics were studied. It is appropriate to clarify the possibility of obtaining ZnO ceramics with only lead oxide, cobalt and other element additives without using bismuth oxide [10-14].
It is dedicated to the preparation of ZnO-PbO-Co3O4-B2O3+H2O3 system ceramics and the study of its electrical properties. After wet grinding, the mixture is dried, then the slurry with a diameter of 12 and a thickness of 1.5-2 mm is pressed from this mixture under a pressure of 35 MPa. Brewing of Shikta was carried out in air with a gradual increase in temperature up to the maximum value (brewing temperature - Tbrew ) at a rate of 400 K/h, keeping at that temperature for 1 hour and gradually cooling down to room temperature at the same rate. The brewing temperature was changed in the range of 1070-1450K. Electrodes made of silver paste were drawn on the polished smooth surface of the stone [1-13]. The volt-ampere characteristic (VAX) of the samples was obtained at constant current. The nonlinearity coefficient of VAX at the current density j=10 P-3 A/cm 2 =lg[(I2 /I1 )/(U2 /U1 )], calculated using the formula. Here I is the current passing through the sample, U is the voltage. The opening voltage of the electric field was taken at the value of the current j=10-3 A/cm 2 . The average size of ZnO grains (1э ) was determined by optical microscopy (ALTAMI-3) of samples grafted in 10% hydrochloric acid solution . The density of cooked slush is estimated by the formula Y=(D0 /D), where D0 and D are the diameter of the slush before and after brewing [20-27].
Experimental results and their analysis. The voltammetric characteristic of the synthesized ceramics is non-linear , which is confirmed by rather large values of the non-linearity coefficient (Fig. 4). As the annealing temperature increases, the nonlinear area of VAX shifts to a smaller value of the electric field, which indicates a decrease in the value of Ex in Figure 5. A decrease of is observed with the increase of brewing temperature. P In the highly non-linear part of VAX, the voltage across the individual boundary of the grains has a value of 3.5 V [13] and is quite weakly dependent on the current. Therefore, the reason for the decrease of E1 with the increase of T dem is the increase of the average size of the ZnO grain, which was studied experimentally (Fig. 5 b, curve 2). At this time, as in the ZnO-PbO-Co3O2 -B2O3 +H2O3 system, titanium dioxide An elongated granule is formed by the addition of . The increase of l 3 in the small area of VAX causing it to slide (picture 4). The non-
linearity coefficient is small and its decrease is observed with the increase of brewing temperature
(Fig. 4 curve 2).
Figure 4. ZnO-PbO- Co2Os-B2Os +H2O3 (1) and titanium dioxide (2) added ZnO-dependence of the non-linearity coefficient on ceramic synthesis temperature [19].
Figure 5. ZnO-PbO -Co2 O3 -B2O3+H2O3 (1) in ZnO- ceramic with added titanium dioxide (2). 10 "3 A/cm 2 on the synthesis temperature of ceramics [19].
40 1
35
30 25 20 15 40 5
1.41 1.3 1.2 1.1 1.0 0.9 0.8 0.7 06 0.9
T.K
1150 1200 T.K
Figure 6. ZnO-PbO -Co2O3-B2O3+H2O3 (2) and titanium dioxide (1) in ZnO- ceramira added lpart.
Dependence of the product E1 (a) and the average value of zinc oxide particles (b) on the synthesis
temperature of ceramics [20].
Properties observed in ceramics with ZnO-PbO- Co2O3-B2O3+H2O3 system - the effect of brewing temperature T and the growth of ZnO grain sizes with the help of TiO2 addition, resulting in the shift of the nonlinear part of VAX The properties of ZnO-PbO-Co2O3 -B2O3+H2O3 system ceramics are similar. The only difference is the significant decrease of with the increase of T- P (Fig. 6). In order to clarify the possible reason for this phenomenon, let's analyze the physico-chemical processes during brewing of the investigated ceramics. Of the pressed ZnO-PbO-Co2O3 -B2O3+H2O3 slag, melting of the PbO-based phase occurs, which is confirmed by the noticeable value of compression (usadka) of the sample baked at 930K y=20% and during its change at the temperature of 1020-1300K, T does not depend. When heated, the mass of ice also decreases. The mass loss up to ~ 760K can be attributed to the evaporation of PbO or this oxide-based intergranular phase starting from ~1040K (after the formation of the liquid phase after 930K) as a monotonous loss of mass by desorption of water or gases from the surface of the oxides. The phenomenon of evaporation of PbO when heated is known and in the literature is discussed [12-18]. Therefore, it can be assumed that the loss of PbO from the sample occurs starting from 1040K. The reduction of the mass of the cooked slag due to PbO, probably, the increase of the storage time at T, leads to a decrease of 13 , while the brewing at higher temperatures leads to a noticeable increase in the porosity of the sample. For the samples without PbO addition or with Bi2 O3 addition instead of PbO, mass loss, decrease of nonlinearity coefficient and increase of porosity during heating up to 1420 K temperature are not noticeable. Therefore, the observed decrease in mass during the heating of the shale can be attributed to the evaporation of PbO or its underlying phase. Baking ceramics in nitrogen reduces its electrical resistance to 102 Om cm in an oxygen-free furnace, the nonlinearity property deteriorates, and the nonlinearity coefficient does not exceed 4-7.
In oxygen, the nonlinearity coefficient increases to 58. Cooking in air is less effective than cooking in oxygen, P=30-40. In order to improve varistor properties, a new brewing method is proposed in the work. So, since it becomes easier for oxygen to pass through porous ceramics at 850-950 0C, oxygen was supplied to the furnace. Ceramics brewed by the proposed method have good varistor properties: P=80-90, Uk =(330-350)V. In order to increase the potential barrier on the surface and the non-linearity of VAX, intensively fired ceramics were reheated in the mentioned environments. The initial nonlinearity factor was 22-30 at Uk =300V. The coefficient of non-linearity gradually decreases up to 12 with the increase of heat treatment temperature in nitrogen, but increases up to 33 when kept at 4000C for 1-2 hours. The growth of the potential barrier at the grain boundary was associated with the formation of the (ZnO+N2) complex. Oxygen baking and repeated heat treatment lead to obtaining ceramic varistors with highly nonlinear properties. A new cooking method and heat treatment mode are proposed. An increase in non-linear properties of ceramics was determined after heat treatment in oxygen at 400° C for 1-2 hours. More valuable information in this area is provided by Masanari Inoda [146]. In order to study the chemistry of intermediate phases, by studying O, ZnO, Sb2O3, Bi2O3 , MnO2 , Cr2O3, Co3 O4 compounds in the form of ternary and quaternary systems, he found spinel-structured ZnCr2 O4, Zn7 Sb2O12, Co7 Sb2 O12, CrBi2 SbO?, MnBiSbO?, 14Bi2 O3&2O3 , 12Bi2O3 Cr2 O3 , (In,Co)7Sb2O12, Zn2 Bi3 Sb3 O14, Co3 Bi3 Sb3 O14 phases have been shown. In order to confirm that those phases are actually formed in our proposed synthesis mode, the compounds were prepared and synthesized in the mode shown in the examples. Table 1 shows the atomic percentage composition of the studied samples. Different phase composition of ceramics can cause chemical changes at the boundary of its grains.
Table 1.
Composition of samp
An example Mrs Bi St Mn Co О
Ki Zn7 Sb2 Ol2 33,3 3 - 9.52 - - 57,14
K2 Bi6 Sb2 Zn4 Ol8 13,3 3 20 6.67 - - 60
Кз Zn2 Bi3 Sb3 Oi4 9.09 13.6 4 13.64 - - 63,63
K4 Bio.6 Mno.4Zni.2 Sbl.8 O 7 - 6,12 18,37 4.0 8 - 71.43
K5 Zn2.1 Coo.2 Sbo.67 O4 30,1 3 - 9.61 - 2.87 57.3
es in atomic %
Table 2.
Composition of some possible intermediate phases
N o Hypothetical formula The amount of components per 10 g
ZnO Sb2 O3 Bi2O3 MnO2 ^3О4
K1 Zn7 Sb2 O12 6.6148 3.3852 - - -
K2 Zn4 Bi6 Sb2 O18 1.6154 1.4468 6.9378 - -
K3 Zn2 Bi3 Sb3 O14 1.2540 3.3658 5.3802 - -
K4 Zn1.2 Bi0.6 Mn0.4 Sb1.8 O7 1.8266 4.9078 2.6150 0.6505 -
K5 Zn2.1 Co0.2 Sb0.67 O4 6.01478 3.42019 - - 0.56506
As can be seen, the line radiographs differ from each other at a fundamental rate, and none of them should contain the free ZnO phase. Because the intense reflection of 2.7939 A°, 1.9019A° characteristic of ZnO is not observed in other line radiographs. Dispersion of free Sb203 and Bi203 phases is not observed in K1-K5 compositions. The realization of these phases occurs due to the introduction of oxygen from the outside (from the air) into the reacting mass. Because the amount of oxygen in the reaction product is greater than the oxygen of the taken components. Of course, at this time, the degree of oxidation of some elements increases. ZnO-PbO-Co3O4-B2O3+H2O3 system ceramics are characterized by high non-linear VAX. The observed decrease of the nonlinearity coefficient with the increase of the annealing temperature in the range of 1070-1420K is caused by the partial evaporation of PbO, which results in the change of the grain boundary parameters in the ceramic sample. ZnO-PbO- Co3O4-B2O3+H2O3 system ceramics with high nonlinear VAX were synthesized. It is shown that the observed decrease of the nonlinearity coefficient with the increase of the annealing temperature in the range of 1070-1420K is caused by the partial evaporation of PbO, which results in the change of the grain boundary parameters in the ceramic sample. The electrical conductivity process in SnO2-ZnO-Bi2O3-GeO2,-H2O3 based ceramics is determined by the potential barrier (barrier) formed at the boundary of SnO2 particles and holding the main charge carriers. A new cooking method and heat treatment mode are proposed. It has been shown that the non-linear properties of ceramics increase after heat treatment at 400° C for 1-2 hours in an oxygen environment.
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