INFLUENCE OF Mn+2 IN THE STRUCTURAL AND ELECTRICAL ...
INFLUENCE OF Mn+2 IN THE STRUCTURAL AND ELECTRICAL PROPERTIES OF (MnO)x(CoO)1-x(Al2O3) SEMICONDUCTORS SYSTEM K. Q. Gomes1*; A.B. Silva2; C. Gibertoni3 1
Department of Engineering and Computer Science, Centro Universitário Norte do Espírito Santo/UFES, BR 101-North, Km 60, Litorâneo District, CEP 29932-540, São Mateus City, ES, Brazil; fax: +55(27)33121566. 2 Department of Materials Engineering, University of São Paulo, Trabalhador Saocarlense Avenue, 400, Centro, CEP 13560-970, São Carlos City, SP, Brazil. 3 Department of Materials Engineering, Federal University of São Carlos, Washington Luís Righway, km 235, CEP 13565-905, São Carlos City, SP, Brazil. [email protected]
Pellets ceramic of (MnO)x(CoO)1-x(Al2O3) were investigated by powder X-ray diffraction method, and electrical analysis by two points method and complex impedance. The manganese oxide was added to the system at molar fraction ratios (x = 0.05, 0.30, 0.50, 0.70, 0.95). The samples were sintering at 1773 K. The X-ray diffraction results were refined by Rietveld analysis, and thus, we could determine the type of system’s structure as spinel. The electrical analysis results indicated a decrease of the DC resistivity with increasing of temperature. In addition, the result of the AC electrical response (impedance spectroscopy) showed that at lower frequencies the largest contribution to the conductivity of the sample comes from the grain boundary.
Keywords: Impedance spectroscopy, electrical properties, X-ray diffraction, spinel.
Introduction Some transition metals (Cu, Mn, Fe, Co, Zn, etc.) are used as gas, temperature, and humidity sensor). The low cost relative of oxide materials based transition metals make them be the subject of several studies [Hotovy, 1999; Bae, 1999; Oh, 2009]. In addition, these compounds have a spinel structure type belongs to Fd3m group with structural formula AB2O4. The unitary cell of this structure contains 32 oxygen atoms compressed in a cubic structure. The main interesting about studies of CoAl2O4 materials based [Zasada, 2014] is the fact that they exhibit similar characteristics to the CuAl2O4 [Gomes, 1998], but with more resistive electrical response. Therefore, this paper aimed to investigation of addition effect of Mn+2 ions in the structural and electrical properties of the MnO-CoO-Al2O3 spinel system oxide composed. Experimental part Chemical compounds used to sintering of the samples in adequate proportions were: Ammonium Oxalate (Merck), powder of Aluminum Oxide (Alcoa, A-16, 98,8% pure),
Cobalt Sulfate (LabSynth, 99,0% pure), Manganese Sulfate (Mallinckrodt, 99,68% pure), and deionized water. Composition of the samples, in pellets format, was followed by the stoichiometry: (MnO)x(CoO)1-x(Al2O3), with molar fraction x = 0,05; 0,30; 0,50; 0,70 e 0,95. In addition, the proportions of the substance were considered according to stoichiometry formulation 1:1. Technique of the X-ray diffraction powder, XRD, was used to identification of the crystalline phases present on the samples. The measures have been performed in an Xray Siemens Diffractometer D5005, using CuK radiation, 40 kV, and 30 mA. The scanning was accomplished to step 0.033° (2) and 3 s counting time. Electrical DC resistivity has been measured using the method of two points (two terminals), through multimeters (HP3457A and HP3458A), of a chamber of controlled temperature (Tmáx = 723 K), of a microcomputer with interface card HP-IB, and of the HPVEE 3.0 software. Electrical AC resistivity measures were obtained by HP 4192A impedancimeter in the 5 Hz to 13 MHz frequency range at room temperature. Results and discussion Figure 1 shows the XDR patterns of the sintered samples at 1773 K for 5 hours. The XRD analysis shows the presence of phases of the Al2O3 (Alumine) and MnxCo1-xAl2O4 (spinel-aluminate).
Fig. 1. XRD patterns of the MnxCo1-xAl2O4 samples.
Fig. 2. Rietveld diffratogram of the Mn0,5Co0,5Al2O4 sample.
Figure 2 shows a typical diffractogram of the phase structure identification in the samples by Rietveld refinement. The quantitative result of the refinement showed a good adjustment of the calculated profile by Rietveld method about the observed profile by XRD. Moreover, it was possible to verify that the MnxCo1-xAl2O4 spinel phase had the biggest percentage in mass fraction. This fraction corresponds to 86% of mass fraction total of the sample. According to the adjustment of structural parameters, the solid solution's phase was identified as belonging to the space group Fd3m. DC resistivity's result shows the decreasing of sample's resistivity with the increasing of temperature. At low temperatures, the resistivity values obtained were about 1010 .cm, which is considered very resistive to the semiconductor oxides [Philip, 1999]. At higher test’s temperatures, the resistivity values reached the order of magnitude of 106 .cm (Figure 3).
Fig. 3. (MnO)x(CoO)1-x(Al2O3) samples with composition: 0,05 x 0,95.
Table 1 shows the estimated values of the samples’ resistivity through extrapolation of semicircles according to diagram complex impedance. Table 1. Results of impedance analysis of the (MnO)x(CoO)1-x(Al2O3) samples.
Fração X 0,05 0,30 0,50 0,70 0,95
Rg () (→) 64 42 68 47 275
Rg + Rcg Rcg () (→0) 6,1E5 12,2E5 52,2E5 14,3E5 0,34E5
cg(-1) 1,6 0,82 0,19 0,69 30,3
The higher conductivity (cg), of the system was obtained to the greater quantity of manganese oxide. The result shows that at low frequencies the major contribution on the resistivity volume is of the grain boundary. Conclusion XRD analysis indicated the presence of Al2O3 and MnxCo1-xAl2O4 phases in the samples. The Rietveld method to the spinel phase showed that the addition of Mn+2 ions increased the lattice parameters. The system indicated a characteristic behavior of a semiconductor. Samples, with a considerable quantity of Co+2 distributed in octahedral sites, indicated an inhibition of electron’s exchange between Mn+2 and Mn+3 ions in octahedral sites causing superior values of the system resistivity. References [1] Hotovy, I., Huran, J., Spiess, L., Hascik, S., Rehacek, V., 1999. Preparation of nickel oxide thin films for gas sensors applications. Sensors and Actuators B, v 57, 147-152. [2] Bae, H. Y., Choi, G. M., 1999. Electrical and reducing gas sensing properties of ZnO and ZnO-CuO thin films fabricated by spin coating method. Sensors and Actuators B, v 55, 47-54. [3] Oh, S., Myung, S., Kang, H. B., Sun, Y., 2009. Effects of Co doping on Li[Ni0.5CoxMn1.5−x]O4 spinel materials for 5V lithium secondary batteries via Coprecipitation. Journal of Power Sources, 189, 752–756. [4] Zasada, F., Grybo, J., Indyka, P., Piskorz, W., Kaczmarczyk, J., and Sojka, Z., 2014. Surface Structure and Morphology of M[CoM']O4 (M = Mg, Zn, Fe, Co and M' = Ni, Al, Mn, Co) Spinel Nanocrystals – DFT+U and TEM Screening Investigations. J. Phys. Chem. C, 1-47. [6] Gomes, K. Q., 1998. Análise Quantitativa de fases espinélio do sistema CuO-Al2O3 com adições de MnO e NiO. Dissertação apresentada ao programa de pósgraduação em Engenharia dos Materiais – DEMa/UFSCar, São Carlos-SP, 121 p. [7] Philip, J., Kutty, T. R. N., 1999. Colossal magnetoresistance of oxide spinels, CoxMn3-xO4. Materials Letters, v 39, 311-317. Acknowledgement: UFSCar
Department of Engineering and Computer Science, Centro Universitário Norte do Espírito Santo/UFES, BR 101-North, Km 60, Litorâneo District, CEP 29932-540, São Mateus City, ES, Brazil; fax: +55(27)33121566. 2 Department of Materials Engineering, University of São Paulo, Trabalhador Saocarlense Avenue, 400, Centro, CEP 13560-970, São Carlos City, SP, Brazil. 3 Department of Materials Engineering, Federal University of São Carlos, Washington Luís Righway, km 235, CEP 13565-905, São Carlos City, SP, Brazil. [email protected]
Pellets ceramic of (MnO)x(CoO)1-x(Al2O3) were investigated by powder X-ray diffraction method, and electrical analysis by two points method and complex impedance. The manganese oxide was added to the system at molar fraction ratios (x = 0.05, 0.30, 0.50, 0.70, 0.95). The samples were sintering at 1773 K. The X-ray diffraction results were refined by Rietveld analysis, and thus, we could determine the type of system’s structure as spinel. The electrical analysis results indicated a decrease of the DC resistivity with increasing of temperature. In addition, the result of the AC electrical response (impedance spectroscopy) showed that at lower frequencies the largest contribution to the conductivity of the sample comes from the grain boundary.
Keywords: Impedance spectroscopy, electrical properties, X-ray diffraction, spinel.
Introduction Some transition metals (Cu, Mn, Fe, Co, Zn, etc.) are used as gas, temperature, and humidity sensor). The low cost relative of oxide materials based transition metals make them be the subject of several studies [Hotovy, 1999; Bae, 1999; Oh, 2009]. In addition, these compounds have a spinel structure type belongs to Fd3m group with structural formula AB2O4. The unitary cell of this structure contains 32 oxygen atoms compressed in a cubic structure. The main interesting about studies of CoAl2O4 materials based [Zasada, 2014] is the fact that they exhibit similar characteristics to the CuAl2O4 [Gomes, 1998], but with more resistive electrical response. Therefore, this paper aimed to investigation of addition effect of Mn+2 ions in the structural and electrical properties of the MnO-CoO-Al2O3 spinel system oxide composed. Experimental part Chemical compounds used to sintering of the samples in adequate proportions were: Ammonium Oxalate (Merck), powder of Aluminum Oxide (Alcoa, A-16, 98,8% pure),
Cobalt Sulfate (LabSynth, 99,0% pure), Manganese Sulfate (Mallinckrodt, 99,68% pure), and deionized water. Composition of the samples, in pellets format, was followed by the stoichiometry: (MnO)x(CoO)1-x(Al2O3), with molar fraction x = 0,05; 0,30; 0,50; 0,70 e 0,95. In addition, the proportions of the substance were considered according to stoichiometry formulation 1:1. Technique of the X-ray diffraction powder, XRD, was used to identification of the crystalline phases present on the samples. The measures have been performed in an Xray Siemens Diffractometer D5005, using CuK radiation, 40 kV, and 30 mA. The scanning was accomplished to step 0.033° (2) and 3 s counting time. Electrical DC resistivity has been measured using the method of two points (two terminals), through multimeters (HP3457A and HP3458A), of a chamber of controlled temperature (Tmáx = 723 K), of a microcomputer with interface card HP-IB, and of the HPVEE 3.0 software. Electrical AC resistivity measures were obtained by HP 4192A impedancimeter in the 5 Hz to 13 MHz frequency range at room temperature. Results and discussion Figure 1 shows the XDR patterns of the sintered samples at 1773 K for 5 hours. The XRD analysis shows the presence of phases of the Al2O3 (Alumine) and MnxCo1-xAl2O4 (spinel-aluminate).
Fig. 1. XRD patterns of the MnxCo1-xAl2O4 samples.
Fig. 2. Rietveld diffratogram of the Mn0,5Co0,5Al2O4 sample.
Figure 2 shows a typical diffractogram of the phase structure identification in the samples by Rietveld refinement. The quantitative result of the refinement showed a good adjustment of the calculated profile by Rietveld method about the observed profile by XRD. Moreover, it was possible to verify that the MnxCo1-xAl2O4 spinel phase had the biggest percentage in mass fraction. This fraction corresponds to 86% of mass fraction total of the sample. According to the adjustment of structural parameters, the solid solution's phase was identified as belonging to the space group Fd3m. DC resistivity's result shows the decreasing of sample's resistivity with the increasing of temperature. At low temperatures, the resistivity values obtained were about 1010 .cm, which is considered very resistive to the semiconductor oxides [Philip, 1999]. At higher test’s temperatures, the resistivity values reached the order of magnitude of 106 .cm (Figure 3).
Fig. 3. (MnO)x(CoO)1-x(Al2O3) samples with composition: 0,05 x 0,95.
Table 1 shows the estimated values of the samples’ resistivity through extrapolation of semicircles according to diagram complex impedance. Table 1. Results of impedance analysis of the (MnO)x(CoO)1-x(Al2O3) samples.
Fração X 0,05 0,30 0,50 0,70 0,95
Rg () (→) 64 42 68 47 275
Rg + Rcg Rcg () (→0) 6,1E5 12,2E5 52,2E5 14,3E5 0,34E5
cg(-1) 1,6 0,82 0,19 0,69 30,3
The higher conductivity (cg), of the system was obtained to the greater quantity of manganese oxide. The result shows that at low frequencies the major contribution on the resistivity volume is of the grain boundary. Conclusion XRD analysis indicated the presence of Al2O3 and MnxCo1-xAl2O4 phases in the samples. The Rietveld method to the spinel phase showed that the addition of Mn+2 ions increased the lattice parameters. The system indicated a characteristic behavior of a semiconductor. Samples, with a considerable quantity of Co+2 distributed in octahedral sites, indicated an inhibition of electron’s exchange between Mn+2 and Mn+3 ions in octahedral sites causing superior values of the system resistivity. References [1] Hotovy, I., Huran, J., Spiess, L., Hascik, S., Rehacek, V., 1999. Preparation of nickel oxide thin films for gas sensors applications. Sensors and Actuators B, v 57, 147-152. [2] Bae, H. Y., Choi, G. M., 1999. Electrical and reducing gas sensing properties of ZnO and ZnO-CuO thin films fabricated by spin coating method. Sensors and Actuators B, v 55, 47-54. [3] Oh, S., Myung, S., Kang, H. B., Sun, Y., 2009. Effects of Co doping on Li[Ni0.5CoxMn1.5−x]O4 spinel materials for 5V lithium secondary batteries via Coprecipitation. Journal of Power Sources, 189, 752–756. [4] Zasada, F., Grybo, J., Indyka, P., Piskorz, W., Kaczmarczyk, J., and Sojka, Z., 2014. Surface Structure and Morphology of M[CoM']O4 (M = Mg, Zn, Fe, Co and M' = Ni, Al, Mn, Co) Spinel Nanocrystals – DFT+U and TEM Screening Investigations. J. Phys. Chem. C, 1-47. [6] Gomes, K. Q., 1998. Análise Quantitativa de fases espinélio do sistema CuO-Al2O3 com adições de MnO e NiO. Dissertação apresentada ao programa de pósgraduação em Engenharia dos Materiais – DEMa/UFSCar, São Carlos-SP, 121 p. [7] Philip, J., Kutty, T. R. N., 1999. Colossal magnetoresistance of oxide spinels, CoxMn3-xO4. Materials Letters, v 39, 311-317. Acknowledgement: UFSCar
