Energy
Procedia
Energy Procedia 00 (2011) 000–000
www.elsevier.com/locate/procedia
MEDGREEN 2011—LB-P2
TiO2 doped with SnO2 and studing its structurail and
electrical properties
Mustafa Afuyonia , Ghassan Nashed, ISSam Mohammed Nasserb
a Department of Physics college of Science University of Aleppo, Syria
b Post-Graduated Student (Master) University of Aleppo, Syria.
Abstract
In this research we prepared a ceramic sample of (TiO2) doped with different ratios of
(SnO2) to produce a humidity sensor , that is applied in many important electronic and
industrial fields. As well , to get better electrical conductance . The work was done
according to the diagram (1) . The samples were prepared by (Sol-Gel) technology ,
during three stages : (solution , gel , powder). The samples were studied by (XRD)
to determine the crystal structure, the prepared samples of (TiO2) doped with (SnO2)
showed poly-crystal structure , and grain size has nano-dimensions between
(40 nm and 65 nm) ,The electrical properties of the samples were studied too ,The
study of the prepared samples showed electrical resistance (6x108 Ω - 1x106 Ω) , its
conductivity increased when humidity increase (%RH), Whenever the ratio of (SnO2)
increased against (TiO2) , the electrical conductivity would increase . By using Mott
Schottky equation the concentration of free electrons (ND) in (TiO2) , and this showed
that not only the shallow charges contributed in conductivity , but the deep charges
contributed , too , when the voltage increased (V) .
Keywords: TiO2 doped with SnO2; TiO2-SnO2; structurail and electrical properties.
∗ Corresponding author. Tel :+963968486369 . E-mail addresses: yaznnasser@yahoo.com.
E-mail addresses: MBATAL2001@yahoo.com.
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1 – Introduction : Sensors got a big interest and became a basical demand in the industrial and the electronic systems . The humidity sensor is one of these sensors , which can be designed of ceramic materials or compound materials . The ceramic sensors are preferred owing to their stable physical and chemical structure when they are used in the environments ,Generally the designed sensors have excellent resistance as the ceramic materials have good dielectric, The following oxides [Zn0-TiO2-ZrO-SnO2-SiO2] and others are good compound to produce and develop humidity sensors [1], TiO2 among these oxides has good sensitivity toward humidity . Titanium Dioxide has many applications , including humidity sensors that are used in for removing systems on the rear windows ,and white wood coating[2],Titanium Dioxide has three phases: (Anatas, Rutile, brocket) [3-4-7] . The study focused on the Anatas phase. It is n-type semiconductor. When it is heated to high degree (1000Cº nearly) , Anatas turns automatically into Rutile structure , as Rutile is the most common type of( TiO2 ), while Anatas is very rare in nature at about( 600 Cº) , Anatas is n-type semiconductor while Rutile is (p-type) [3] ,It is recorded that the thin film sensors has lower sensitivity than ones showed by their analogues of porous ceramic . The sensitivity response of TiO2 toward recessive gases like (H2 and OH-) and vapor (H2O) is in all directions of absorption and adsorption . But humidity sensitivity come by adsorbed water layers which transferred protons in the porous structure at room temperature (25 Cº) and illumination intensity (436 Lux) . 2 - Experimental work : 2-1 Samples preparation : Beacher was cleaned by chemical solution to remove any suspended fats and impurities on its surface . The samples prepared according to certain criteria as shown by the scheme within the physical and chemicals conditions . TiCl4 solution with high purity (99%) from (PROLABO) and SnCl4 from (PROLABO) were weighed with different ration , as in table 1 . materials were put in a container which big enough for the mixture ,The materials were mixed by magnetic mixer for two hours at 250 rpm . After that the samples were dried and donated with (Z1, Z2, Z3). Table 1: shows the preparation of ceramic samples of TiO2 doped with different ratios of SnO2
Sample
Z1
Z2
Z3
TiO2 ratio
10 gr
8.8 gr
8 gr
SnO2 ratio
0 gr
1.2 gr
2 gr
2-2 working scheme : the scheme(1) shows how to prepare the samples :
Scheme(1) to prepare samples according to different ratios
4 – Experimental measurements
4-1 structure measurements :
To study the ceramic samples (Z1, Z2, Z3)structure which were prepared by using the Xray
deviation meter (XRD) , Philips Model to measure the spectrum of X-ray deviation
for the samples (Z1, Z2, Z3). Figure 1 represents the spectrum of X-ray deviation for the
three samples
.
Figure 1 : the spectrum of X-ray deviation for the three samples.
From the figure 1 it is clear that :
A– Figure 1 represents the spectrum of X-ray deviation for pure SnO2 at 2θ about :
{26.5 – 34 – 38 – 51.8 – 54.5 – 62} degree which meet the following levels : (110 – 101
– 200 – 211 – 220 – 310) , respectively and which conform with the crystal structure of
pure SnO2 .
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B- The scheme 2 represents the spectrum of x-ray deviation for pure TiO2 at 2θ , about
{25.2 – 37.9 – 47.8 – 53.8 – 55 – 63} degree which meet the indexes of the following
levels : (101 – 004 – 200 – 105 – 211 – 204 ), respectively , and which conform the
crystal structure of TiO2 (Anatas). The samples were processed at 600 Cº .
C- The scheme 3 represents the spectrum of x-ray deviation for the sample Z2 . From
the study of the x-ray deviation spectrum it is clear that the formed ceramic material
(TiO2 – SnO2) is poly crystalline owing to the linkage between the elements of the
prepared material , and the lines of XRD conform the ones that recorded for (TiO2 –
SnO2) [5] , the following relation of (Seherer Equation) is applied [1] , which is given in
the following relation (1) :
D = k λ/( cos θ) (1)
Where : D is the size of granule , the wideness of peck opening at the middle of
intensity , measured by Radian , k is constant its value 1 , λ wave length used by XRD
apparatus from Philips and its value λ=0.154 nm , deviation angle . The following
chart gives the size of the formed granules :
Table 2 : the size of the formed granules.
Sample Granule size (nm)
Z1 60.484
Z2 42.394
Table 2 : the size of the formed granules.
6- Measurement of DC :
To study the electrical characters (DC) of the three samples (Z1, Z2, Z3)of
Titanium Dioxide doped with different ratios of SnO2 , an ohm (resistance) connection
was made for the samples via a mask of Aluminum sheet graved by laser (Nd- yag
Laser) on the surface of the sample , as in the figure :
Prepared sample connecting poles
Ohm connecting
Figure 2 : The used mask I the Ohm connecting.
The aspects (I , V) for the three samples, were taken , and the figures (3(a,b,c)) sow the
aspect (I , V) for the ceramic samples (Z1, Z2, Z3), respectively at different values of the
relative humidity (36% , 50% , 70%) :
Figure 3(a) : The aspect (I,V) for the samples (Z1, Z2, Z3)at 36% relative humidity Figure 3(b) : The aspect (I,V) for the samples (Z1, Z2, Z3) at 50% relative humidity Figure 3(c) : The aspect (I,V) for the samples (Z1, Z2, Z3) at 70% relative humidity. We noticed from studying the diagrams in figures (3(a,b,c)) for the (I.V) aspect changing at the room temperature with stable illumination intensity and stable relative humidity that the relation is non-linear , as its structure is granular and multi-crystallization . The electrical resistance of the ceramic materials is subjected to the relation (2) : where the non-linear resistance was evaluated from the relation (1): I= (2) a : the non-linearity factor . if we take the logarithm of the two sides , we find that , for the current I1 : a: non-linearity factor is calculated by the following relation (3): From the figures (3 , 4 and 5) at different RH% we conclude the following : we calculate the non-linearity factor a of the studied ceramic samples (Z1, Z2, Z3), and the following table shows the values of the non-linearity factor with the changing in the level of the relative humidity of the studied samples at various concentrations .
a
b
c
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Table 3 : the changing in the non-linearity factor according to(Z1, Z2, Z3)
Sample
a non-linearity factor at 36%RH
a non-linearity factor at 50% RH
a non-linearity factor at 70% RH
Z1
2.417
1.5 509
1.353
Z2
2.2098
1.3765
1.201
Z3
1.659953
1.3571
1.012
the changing in the doping ratio at stable relative humidity It is noticed that the values of the non-linearity factor are within (2.417 – 1.012) and it is more than one , which means that the structure of the samples is granular structure , and that the resistance of these samples integrate with the surface character of these samples when there is changing in the non-linearity factor a . Table 4 shows this . Table 4 : the R values at different non-linearity factor (a) for the three samples .
sample
R(Ω) at RH = 36%
R(Ω) at RH = 50%
R(Ω) at RH = 70%
Z1
6.65 x 108
1.56 x 108
8.23 x 107
Z2
2.11 x 108
9.6 x 107
2.34 x 107
Z3
2 x 108
4.23 x 107
7.33 x 106
The tables (3 , 4) show that non-linearity factor (a) decreases when the relative humidity increases , also when the doping ratio with SnO2 increases , so we get non-linearity relation . And that the resistances R(Ω) decreases when the relative humidity of the three samples (Z1, Z2, Z3)increases . By electrometer from (Kaittvel) we measure the resistance R(Ω) of the prepared samples at different relative humidity levels .and the studying of the samples characters at different relative humidity levels , and the control opening for the humidity values , increasing or decreasing , and after taking the resistance values of the three samples at different relative humidity levels and drawing the aspect (R(Ω),%RH) . Figure( 4) shows the resistance R(Ω) changing according to the relative humidity level of the samples Z1 and Z2 .
Figure 4 : the resistance R(Ω) changing according to the relative humidity level to the three samples (Z1, Z2, Z3) . Notice from the figure 4 that the resistance changes from 6x106(Ω) to 1x106(Ω) , when the relative humidity changes from RH = 1% to RH = 70% , for the prepared samples . It is found that the relation between R(Ω) and RH% is a linear relation from (RH = 10% to RH = 70%) . That means we can use the samples as humidity sensors from (RH=10% to RH=70%). Besides, the increasing in the doping ratio increases the conductivity of the formed sensor at certain value , where we notice a gluttony to OH- on the porosity of the conductor surface . Also , when the relative humidity increases RH% at each samples there will be decreasing in the resistance values . This leads us to a conclusion that the conductivity increases when the humidity increases [1] . 5-3-2 Measuring the AC : By the analyzer of gain and phase from (Solectron 1255) , when we apply a voltage value 5(V) and a resistance Ra = 220 Ω with a frequency range 10 Hz to 20000 Hz . The relation is drawn between the nodal part X(W) with the real part R(W) of the nodal reluctant given by the following relation of the three samples (Z1, Z2, Z3). The representation of the reluctant is given by the nodal form the relation 4 . Z=R(W)+JX(W) (4) Figure 9 shows the spectrum of nodal reluctant between the nodal part X(W) and the real part R(W) of the three samples at relative humidity level 35.5% .
a
b
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Figure 5(a) : nodal reluctant spectrum of the samples (Z1, Z2, Z3) at RH = 35.5% . Figure 5(b) : nodal reluctant spectrum of the samples (Z1, Z2, Z3) at RH = 50% . Figure 5(c) : nodal reluctant spectrum of the samples(Z1, Z2, Z3) at RH = 70% . Figure 6: changing in nodal reluctant according to the changing in relative humidity . It is found from the figure 6 that there is decreasing in the reluctant when we increase the humidity , The studied samples are subjected to Debby model where : A- The spectrum of the nodal reluctant of the prepared ceramic samples are regular semi-circles . This implied that the granular structure of the samples is homogeneous structure . B- As the values of R(W) decrease whenever the frequency (Hz) increases , the equal circuit between each two near granules is a resistance and a capacitor parallel connected . When we draw the relation between and V when applying a frequency 20 KHz of the three samples , we find the following lines , which we can determine via them the intensity of the atoms and the effect of doping by SnO2 with TiO2 . Figure 7 : The aspect according to V for the sample Z1& Figure 8 : The aspect according to V for the sample Z2.
c
Figure 9 : The aspect according to V for the sample Z3 The intensity of the donor electrons are calculated from the relation (5) : Where : The charge of electron : q=1.6x10 -19 C The isolation constant for Titanium Dioxide at 600 C: [8],De-electricity constant ( = 8.85 x 10-12 F/M),The area of the ohm connecting surface of the sample A = 4x10-6 (m2). Concentration of electrons :ND It is found that the value of ND for the samples (Z1, Z2 , Z3) from the curves clarified by the figure (7 , 8 and 9) are : Table 4 : Concentration of charges(ND) cm-3 for the samples (Z1 , Z2 , Z3)
Sample
Concentration of charges(ND) cm-3
Z1
6.92367x1017
Z2
1.1869x1018 , 8.3084x1017
Z3
2.0771x1018
ND (Z2) = 1.1869x1018 cm-3: the concentration of the surface electrons and the deep ones . So the intensity of the free charge (electrons) which come from deepness and contribute in the conductivity of the second sample is : ND(Z2)=3.5606x1017 cm-3 ,which contributes in increasing the electricity conductivity , ND (Z3) = 2.0771x1018 cm-3 increases whenever the doping ratio increases . It is noticed that there is an increasing in the electrons intensity ND when we increase the doping ration , hence the increasing in the electricity conductivity for the doped samples . It is noticed , too , that the index ( is increasing index with the applied voltage . This means that the formed semi-conductor is (n) type . This represents the fact that the sensor formed from Titanium Dioxide and processed to the temperature 600 C is Anatas phase .
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