Electrical and dielectrical properties of the MnO 2 doped with As 2 O 3 and SnO

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1 Materials Letters 58 (2004) Electrical and dielectrical properties of the MnO 2 doped with As 2 O 3 and SnO A. Kayan a, E. Tarcan b, U. Kadiroglu a, K. Esmer b, * a Department of Chemistry, Faculty of Science and Arts, Kocaeli University, Kocaeli, Turkey b Department of Physics, Faculty of Science and Arts, Kocaeli University, Kocaeli, Turkey Received 2 October 2003; received in revised form 15 January 2004; accepted 23 January 2004 Available online 27 February 2004 Abstract The effects of solid solid interactions of As 2 O 3 and SnO doped in MnO 2 were investigated. The electrical and dielectric properties of the produced composite were also studied. Pure MnO 2 and doped solids having different concentrations of As 2 O 3 and SnO were subjected to heat treatment at 700 jc for 24 h. The optical investigations show that As 2 O 3 reacts with MnO 2 to give mixed oxide system. The space charge polarization increases depending on SnO effect and the resulting samples demonstrate semiconductor behaviour. When the amount of As 2 O 3 is increased, the conductivity increases proportionally. Dielectric constant was calculated to be f 41 at 1 MHz, and dielectric constant and loss factor are decreased at high frequencies. In dielectric relaxation, arsenic ions play an effective role and the structure illustrates dipolar relaxation behaviour. D 2004 Elsevier B.V. All rights reserved. Keywords: Manganese (IV) oxide; Arsenic (III) oxide; Electrical and dielectric properties 1. Introduction Composites comprise a very broad and important class of engineering materials. They are used in a wide variety of applications such as mobile communication systems. Moreover, there is considerable scope for tailoring their structure to suit the service conditions. Accordingly, there have been several works conducting with different metal oxides in order to suit such conditions [1 5]. Previously, composites containing oxides such as B 2 O 3, SiO 2, MnO, P 2 O 5, GeO 2, V 2 O 5, As 2 O 3, etc. were investigated [6 9]. Manganese ions, Mn 2+ and Mn 3+, can easily make octahedral and tetrahedral coordination by oxides mentioned above. Although in most studies MnO is used as a doped material because of its different valence oxidation state in different mixed oxide system [9], MnO 2 has not considered as a base material yet. A study of Mn Sn As mixed oxide systems has not been reported, either. * Corresponding author. Tel.: /267; fax: address: ekadir@kou.edu.tr (K. Esmer). Investigations have been carried out in recent years structural, electrical, optical and dielectrical properties of such materials. Different techniques, e.g., FTIR, XRD and impedance have been employed to examine the properties of the materials. Frequencies and relative intensities of IR absorption bands are sensitive to coordination geometry and oxidation states [10]. FTIR technique though is a powerful tool for analysing the response of materials and it should be supported by other techniques such as XRD, which gives information about the formation of the composite. FTIR, XRD and impedance techniques are adopted in this study for investigating structural, electrical and dielectrical properties of Mn As Sn oxide composite at different contents. 2. Experimental The chemicals, manganese (IV) oxide (MnO 2, 90%, Aldrich), Tin (II) oxide (SnO 99%, Aldrich) and arsenic (III) oxide (As 2 O 3, 99%, Fluka) were used in the experiments. Firstly, 80 wt.% MnO 2, 10 wt.% SnO and 10 wt.% As 2 O 3 and secondly, 80 wt.% MnO 2, 15 wt.% SnO and X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi: /j.matlet

2 A. Kayan et al. / Materials Letters 58 (2004) wt.% As 2 O 3 oxide mixtures were prepared, respectively. The Mn Sn As oxide mixtures were kept at 700 jc for 24 h and then cooled slowly down to room temperature and milled for 3 h. Then the Mn Sn As oxide powders were pressed at 7 tons to form pellets which have diameter of 13 mm. FTIR spectrum of each mixed system was recorded on Shimadzu 8201/86601 PC spectrometer. The vibrational measurements were performed using pellets. X-ray spectra were carried out on a XRD Rigaku DMAX The distance (d) between electrodes and cross-sectional area (A) for all samples were measured to be and cm 2, respectively. Aluminium was evaporated as electrodes on both faces of the pellets under high vacuum atmosphere. The Univex 300 Leybold Vacuum apparatus was used. The dc conductivity was measured by a Keithley 2400 Source-meter. The capacitive measurements were performed in the frequency range 5 khz 5 MHz and in the voltage range 0 5 V with an Impedance/Gain-Phase Analyzer Hewlett Packard 4194A. All measurements were taken at room temperature. 3. Result and discussion 3.1. Solid solid interactions The infrared spectra of pure MnO 2 (base material) and composite having 80 wt.% MnO 2, 10 wt.% SnO and 10 wt.% As 2 O 3 are given in Fig. 1. The pure MnO 2 gave double degenerate vibrations at cm 1 and strong peaks at 530 and 608 cm 1. The other two pure oxides give bands at cm 1 for SnO [11] and 505, 618, 795 and 1050 cm 1 for As 2 O 3 [12]. This double degenerate peak of MnO 2 appeared at 655 cm 1 as shoulder peak for the composite. The intensity of peak at 540 cm 1, which belongs to pure MnO 2 decreases when 10 wt.% As 2 O 3 was doped (Fig. 1). The band intensity at 618 cm 1 for As 2 O 3 increases somewhat because of overlap with the band at 614 cm 1 for MnO 2. As seen in the figure, two stretching bands at 795 and 1050 cm 1 of As 2 O 3 shifted to around 850 and 990 cm 1 due to interaction of As 2 O 3 with MnO 2. The composite consisting of 80 wt.% MnO 2, 15 wt.% SnO and 5 wt.% As 2 O 3 gave almost same spectrum, however with different intensities. XRD spectra (Figs. 2 and 3) also support FTIR results. The peaks belonging to SnO obscured the presence of the strong peaks of Mn As oxides. XRD patterns especially show that the reaction between MnO 2 and As 2 O 3 produces Mn 2 As 2 O 7 and Mn 2 O 3. As seen in Fig. 3, the peaks assigned to Mn 2 As 2 O 7 were detected at 2h = 27.8j, 29.4j and 33.9j. The additional peaks due to Mn 2 O 3 were also observed at 2h = 23.1j, 32.9j, 38.2j and higher 2h values. The peak intensities at 2h = 26.5j, 33.9j, 38.2j and 51.7j appeared for SnO 2. The overlapped peak at 38.2j for SnO 2 and Mn 2 O 3 can be interpreted as small coordination of SnO into octahedral hole of MnO 2. The formation of Mn 2 As 2 O 7 can be explained that As 2 O 3 links into a tetragonal structure of MnO 2 by sharing oxygen. Similar explanation was suggested by Van Die et al. [8]. Fig. 1. FTIR spectra of composite (80% MnO % As 2 O % SnO) and pure MnO 2.

3 2172 A. Kayan et al. / Materials Letters 58 (2004) Fig. 2. Powder XRD patterns of composite (80% MnO 2 +5%As 2 O % SnO) (a: Mn 2 As 2 O 7,b:Mn 2 O 3, c: SnO 2 ) Electrical conductivity Resistivities and conductivities were calculated with the contribution of equations, q ¼ E J and ðv cmþ ð1þ r ¼ 1 q ðv 1 cm 1 Þ ð2þ Fig. 4. Current versus voltage for composites and pure MnO 2. where, V is the applied voltage, d is the distance between contacts, E = V/d is the electrical field, J = i/a is the current density, and A is the area of pellet as a unit-section. Dc current voltage plots of composites prepared in various contents of SnO and As 2 O 3 are shown in Fig. 4. The amounts of As 2 O 3 have especially significant impacts on the conductivity of MnO 2. In other words, the conductivity was correlated with the doping amount of As 2 O 3. When 5 wt.% As 2 O 3 was doped, the conductivity increased. As the doping amounts of As 2 O 3 increased to 10 wt.%, the conductivity of the oxide mixture markedly increased as seen in Fig. 4. It is also assumed that the SnO content slightly effects the conductivity of composites. These composites demonstrate semiconductor behaviour. In the literature, there are many studies for other mixed oxide systems which show similar behaviour to our results [13 16]. Resistivity corresponds to 1.4 V: q = V cm for pure MnO 2, q = V cm for 5 wt.% As 2 O 3 - doped composite and q = V cm for 10 wt.% As 2 O 3 -doped composite were calculated. Although, the conductivity becomes high due to reaction between MnO 2 and As 2 O 3, it is also assumed that free electrons of SnO and the diffusion of SnO (because of heat treatment at 700 jc) into Mn As oxide structure contribute to the increase of conductivity Dielectrical properties Dielectric constants (evand eu), loss tangent (tan d) and dielectric conductivity (r) were calculated using the following: C ¼ e 0 e A=d tan d ¼ ew ev ð3þ ð4þ and r ¼ xew ð5þ Fig. 3. Powder XRD patterns of composite (80% MnO % As 2 O % SnO) (a: Mn 2 As 2 O 7,b:Mn 2 O 3, c: SnO 2 ). (e 0 : space constant: F/m and x: angular frequency). The plots of ev, eu and tan d versus frequency are shown in Figs The variations corresponding to 5 khz 5 MHz frequencies are interpreted as the following: The dielectric constant, ev, of these composites decreased

4 A. Kayan et al. / Materials Letters 58 (2004) Fig. 5. Variation of real part of dielectric constant, ev, with frequency (Hz). Fig. 6. Variation of imaginary part of dielectric constant, eu, with frequency (Hz). Fig. 7. Variation of loss factor, tan d, with frequency (Hz).

5 2174 A. Kayan et al. / Materials Letters 58 (2004) with an increase in the doping amounts of As 2 O 3 as well as frequencies (Fig. 5). The imaginary part of dielectric constant, eu (10 wt.% As 2 O 3 -doped), increases from f 0.13 at low frequency region (10 khz) to 0.23 making a maximum at frequency f 500 khz and then gradually drops up to high frequency region, 1 MHz. The similar behaviour was seen for 5 wt.% As 2 O 3 -doped composite. These variations in eu values correspond to polarization resonance associated with the lattice vibrations (Fig. 6). We notice a considerable increase of tan d with frequencies (around 500 khz); such a behaviour can only be attributed to space charge polarization and relaxation behaviour [17] due to the bonding Mn O As mentioned earlier in these composites (Fig. 7). The space charge polarization increases depending on weight percent of SnO. As seen in Fig. 7, the space charge polarization for 10 wt.% SnO increases from (15 wt.% SnO doped-composite) to (making a maximum) at about 500 khz. In addition to all of these, we suggest that when SnO content increased, a small amount of MnO 2 participates to the reaction and accordingly the conductivity decreases regarding to 10 wt.% As 2 O 3 content. Detailed information about relaxation measurements depending on temperature can be reached via the investigation of ev and eu variations and the activation energy at fixed temperature. In a study about electrical conduction and dielectric behavior of Gd 1 x Ca x CoO 3 by Mandal et al. [18], it was observed that the dielectric constant decreases with increasing frequencies and constantly varies after 1 MHz. They reported that octahedral hole occupied by Co 3+ and Ca 2+ ions play effective role in the polarization behaviour of the sample. Generally, at different ceramic composite materials, the relative dielectric constant is changed in the range of for advanced capacitors [19]. In this study, the dielectric constant for 10 wt.% As 2 O 3 -doped composite was calculated to be f 41 at 1 MHz. 4. Conclusion The electrical conductivity increases because of the reaction between As 2 O 3 and SnO with MnO 2. As a result of these reactions, the samples showed a semiconductor behaviour. This case relates with increasing the space charge polarization and relaxation behaviour. The amount of MnO 2 (80 wt.%) in composites is more than the other two oxides. However, arsenic ions are more effective in the dielectric relaxation. In these kinds of composites, in order to explain the relation in detail between dielectric relaxation and electrical conduction, it is important to make measurement depending on the temperature. Further investigation about these composites will be continued and expanded. Acknowledgements This work has supported by Research Foundation of Kocaeli University, Project No. 2002/57. References [1] R.N.P. Choudhary, R. Palai, S. Sharma, Mater. Sci. Eng., B, Solid- State Mater. Adv. Technol. 77 (3) (2000) [2] R.C.R. Franko, E.R. Camargo, M.A.L. Nobre, E.R. Leite, E. Longo, J.A. Varela, Ceram. Int. 25 (5) (1999) [3] S. Sharma, R.N.P. Choudhary, S.R. Shanigrahi, Mater. Lett. 40 (1999) [4] H.R. Rukmini, R.N.P. Choudhary, V.V. Rao, Mater. Lett. 37 (1998) [5] A. Gamil, E.-S. Nagi, R.E. Radwan, G. Turky, Solid State Ion. 156 (2003) [6] A. Datta, A.K. Giri, D. Chakravorty, Appl. Phys. Lett. 59 (1991) 414. [7] N. Satyanarayana, A. Karthikeyan, M. Venkateswarlu, J. Mater. Sci. 31 (1996) [8] A. Van Die, A.C.H.I. Leenaers, G. Blasse, W.F. Van Der Weg, J. Non- Cryst. Solids 99 (1988) 32. [9] G. Srinivasarao, N. Veeraiah, J. Alloys Compd. 327 (2001) [10] S.J. Wen, T.J. Richardson, L. Ma, K.A. Striebel, P.N. Ross Jr., E. Cairns, J. Electrochem. Soc. 143 (1996) [11] M.P. Brown, R. Okawara, E.G. Rochow, Spectrochim. Acta 16 (1960) 595. [12] G. Lucovsky, F.L. Galeener, J. Non-Cryst. Solids 37 (1980) 53. [13] W. Zheng, S.C. Wong, Compos. Sci. Technol. 63 (2003) [14] K. Esmer, Mater. Lett. 34 (1998) [15] Y.X. Pan, Z.Z. Yu, Y.C. Ou, G.H. Hu, J. Polym. Sci., Part B, Polym. Phys. 38 (2000) [16] L.C. Costa, F. Henry, M.A. Valente, S.K. Mediratta, A.S. Sombra, Eur. Polym. J. 38 (2002) [17] V. Ravi Kumar, N. Veeraiah, J. Phys. Chem. Solids 59 (1997) 91. [18] K.D. Mandal, L. Behera, K. İsmail, J. Alloys Compd. 352 (2003) [19] D.H. Kuo, C.C. Chang, T.Y. Su, W.K. Wang, B.Y. Lin, J. Eur. Ceram. Soc. 21 (2001)