MATERIALS SCIENCE and TECHNOLOGY Edited by Evvy Kartini et.al.
ELECTRIC AND PYROELECTRIC PROPERTIES OF LiTaO3 AND LiFe2TaO3 FILMS M.N.Indro1, Irzaman1 , B. Sastri1, L. Nady1, H.Syafutra1, Siswadi2 1. Departement of Physcs, Bogor Agricultural University, 2. Departement of Mathematics, Bogor Agricultural University, Jl.Meranti gedung FMIPA, Kampus Dramaga, Bogor 16680, Indonesia. e-mail:
[email protected] ABSTRACT In this research LiTaO3 and LiFe2TaO3 films has been grown on Si substrate using chemical solution deposition (CSD) method accompanied by spin coating technique and followed by an annealing process at a temperature of 850°C for 10 hours. The XRD investigation shows that both of the two samples are crystalline LiTaO3 and LiFe2TaO3. Electric resistance measurement of the LiTaO3 using I-V meter results in agreement with the fact that the sample is dielectric. Electric conductivity of the LiTaO3 film is found to be 3.5 x10-10 S/cm. The doping of 5% Fe on the LiTaO3 results in lowering the conductivity to be around one-third of the original value. Pyroelectric coefficients of the Films were found around 0.0015 C/m2 °C and 0.00026 C/m2 °C for LiTaO3 and LiFe2TaO3 respectively. Key words : LFT, CSD, electrical conductivity, pyroelectric. INTRODUCTION Development of LiTaO3 (LT) and LiFe2TaO3 (LFT) films may be carried out using chemical solution deposition (CSD) method at low temperature (around 700C), and it does not need complicated treatment (S. Amiruddin Et al, 2005). The Films might be used as a charge storage in electronic devices since they have quite a high dielectric constant (A.Maddu,2007). In this investigation the LT film was grown on silicon substrates using CSD method which is followed by spin coating technique and annealing at a temperature of 8500C. The LFT film was also grown using the method above with an additional (doping) of 5% Fe on the LiTaO3 composition. The Fe3+ ion dopant on the LT compound may change its characteristics such as the lattice parameter, dielectric constant, and piroelectric coefficient, since the Fe3+ ions may expell some O2- ions in the LT stucture (P. S. Kirev,1975). EXPERIMENT The raw materials for composing the films are LiO2CH3 99.9%, Ta2O5 99.9%, Fe2O3,2metoxyetanol, Si substrate, aquadest, and HF. The instruments used in this experiment are analitical ballance, spin coater, mortar, measuring glass, furnace, XRD, LCR meter, I-V meter, and osciloscope. The crystal structure of the LT and LFT samples were investigated using XRD. The electric resistance of the samples was measured using LCR meter in several
Materials Science and Technology situations (dark, exposed in 25W, 50W, 75W, and 100W lamps respectively), while the electric conductivity of the samples was calculated using the formula; = L/RA, and the expected chemical reactions for composing the LT and LFT samples are as the following; 2LiO2C2H3 + Ta2O5 + 4O2 2LiTaO3 + 3H2O + 4CO2 2LiO2C2H3 + Ta2O5 + 2Fe2O3 + O2 2LiFe2TaO3 + 3H2O + 4CO2 The pyroelectric investigation was carried out by measuring the voltage and electric currents passing the sample when the each sample was put in a furnace and the temperature are varied from 30o C to around 120o C. RESULT AND DISCUSSION The XRD investigation on the samples results in agreement that the LT and LFT crystals may be grown by CSD technique followed by annealing process. The intensity of the Xray spectrum diffracted by the samples is shown as the Figure 1 (a) and (b) below.
Figure 1: Intensity vs 2 result from XRD of (a) LiTaO3 and (b) LiFe2TaO3 crystals
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Electric and Pyroelectric Properties of LiTaO3...... The Ag peak that appears on the Figure 1 came from the Ag paste attached on the sample as contact points, while the Si peak came from the Si substrate. The current-voltage characteristic of the LiTaO3 sample was measured using I-V meter in two different conditions; dark and bright (exposed by 100 W lamp in a 5 cm distance). The result is shown in the Figure 2 below.
Figure 2: I-V characteristic of the LiTaO3 sample
It is shown that the LT sample has very high electrical resistance (around 1010 ohm) and exhibits a different resistance in a different brightness condition. Based on this result the electric conductions of the LiTaO3 and LiFe2O3 samples were investigated in several brightnes conditions. The electric conductivity of the samples is shown on the Table 1, and the graph associated with the data is shown by the Figure 3. Table 1: Electric Conductivity of the LT and LFT samples
Sample LiTaO3
Electric Conductivity (S/cm) 0 watt
25 watt
50 watt
75 watt
100 watt
3.655 x 10-10 3.658 x 10-10 3.707 x 10-10 3.514 x 10-10 3.831 x 10-10
LiFe2TaO3 (5% Fe) 9.426 x 10-11 1.273 x 10-10 1.259 x 10-10 1.283 x 10-10 1.123 x 10-10
Figure 3: Electric conductivity of the LiTaO3 and LiFe2TaO3 samples
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The electric conductivity data (in the order of E-10) confirmed that the LT and LFT sample are indeed dielectric materials. The electric conductivity of the LFT is lower than that of the LT sample. It is quite surprising since the Fe dopant elemen that is a good conductor does not increase the conductivity of the LT sample. The Figure 3 also shows that the effect of exposing light is not significant in both samples. It seem that the electric conductivity of LT and LFT samples are not sensitive with external light. The pyroelectric investigation on both samples resutls in the current density data at several temperatures as shown in Figure 4. It is shown that both of the LiTaO3 and LiFe2TaO3 samples are pyroelectric materials. The LT sample is more sensitive in responding the temperature change rather than the LFT sample. It is also surprising that the LFT sample shows a constant current density when the temperature is above 800 C. The pyroelectric coefficient of the both sample may be predicted from the slopes of the curves in the Figure 4. It seem that the pyroelectric coefficient of the LT sample is around 0.001 A/m2 0C, while that of the LFT sample is around 0.00025 A/m2 0C.
Figure 4: Current density vs Temperature of the LiTaO3 and LiFe2TaO3 samples
CONCLUSION Hence, It has been proven that the LiTaO3 and LiFe2TaO3 films may be grown on Si substrate using chemical solution deposition (CSD) method accompanied by spin coating technique. The process should be followed by an annealing treatment at a temperature around 850°C for at least 10 hours and should be cooled slowly to the room temperature. The XRD investigation shows that both of the two samples (LiTaO3 and LiFe2TaO3) are solid crystals. Electric resistance measurement of the LiTaO3 using I-V meter results in agreement that the sample is insulator (R is in an order of 1010 ohm). Electric conductivity of the LiTaO3 film is around 3.5 x10-10 S/cm, while that of the LiFe2TaO3 is around 1.2 x10-10 S/cm. It means that the doping treatment with 5% Fe on the LiTaO3 results in lowering the conductivity to be around one-third of the value. Pyroelectric coefficient of the both LT and LFT samples may be predicted from the pyroelectric diagram. It is found that the value of the pyroelectric coefficient of LiTaO3 Film is around 0.0015 C/m2 °C), while that of the LiFe2TaO3 is around 0.00026 C/m2 °C. REFERENCES [1]. A Maddu, 2007. Pedoman Praktikum Eksperimen Fisika 2. Departemen Fisika. Institut Pertanian Bogor.
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Electric and Pyroelectric Properties of LiTaO3...... [2]. Irzaman, Y. Darvina, A. Fuad, P. Arifin, M. Budiman, and M. Barmawi. Physical and Pyroelectrik Properties of Tantalum Oxide Doped Zead Zirconium Titanate Physica Status Solidi (a), Germany, 199(3):416-424. [3]. K. Uchino, 2000. Ferroélectrique Devices. Marcel Dekker. Inc. USA. [4]. M. Jahja, 1997. Penentuan Koefisien Absorpsi Optis Semikonduktor Amorf dan Mikrokristalin Silikon Karbon . Skripsi Sarjana Jurusan Fisika. Depok: Universitas Indonesia. [5]. R. Erviansyah, 2010. Studi Karakteristik Sensor Cahaya Dan Sensor Suhu Berbasis Film Tipis Ba0,25Sr0,75TiO3 (BST) Yang Didadah Ferium Oksida (BFST) Menggunakan Metode Chemical Solution Deposition. Skripsi Sarjana Depertemen Fisika. Institut Pertanian Bogor. [6]. S. Amiruddin, Usman,Mursal, T.Winata, dan Sukirno, 2005. Optimasi Parameter Tekanan Deposisi pada Penumbuhan Lapisan Tipis Polykristal Silikon dengan Metode Hot Wire Cell PECVD. Jurnal Matematika da Sains 10(1):27-30. [7]. Sutrisno, 1986. Elektronika Teori dan Penerapannya. Bandung : Institut Teknik Bandung. [8]. X Liu. 2005. Nanoscale chemical etching of near-stoichiometric lithium tantalite. Journal Material Sains 97(1):30-38. [9]. Y. Kazuhisa, 1993. Domain inversion in LiTaO3 using proton exchange followed by heat treatment. Journal of Applied Physic 75(3):1312-1320.
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