Jurnal Penelitian Sains Volume 14 Nomer 4(B) 14405

The E�ect of Sintering Temperature on The Properties ofCaCu3Mn4O12 (CCMO) Synthesized Via Solid State Reaction

Agus Setyo BudiMaterial Science, Physics Department-Faculty of Science State University of Jakarta, Indonesia

Intisari: Sintesis CaCu3Mn4O12 (CCMO) telah berhasil dilakukan dengan metode reaksi fasa solid . Senyawa oksidakomersial yaitu kalsium karbonat, tembaga oksida dan mangan oksida digunakan untuk preparasi CCMO. Karbonat danoksida ditimbang berdasarkan rasio stoikiometri dan dicampur menggunakan ball milling selama satu jam. Campurankemudian dikalsinasi pada suhu 850�C selama 12 jam dan disintering pada suhu 1000�C, 1050�C, 1070�C dan 1090�Cselama 24 jam. Pembentukan CCMO ditunjukkan melalui difraksi sinar-X (XRD). Analisis mikrostruktur dilakukan de-ngan menggunakan Scanning Electron Microscope (SEM), sedangkan kerapatan dan porositas bulk diukur menggunakanteknik Archimedes. Efek suhu selama sintering pada mikrostruktur dan sifat listrik juga dilakukan. Campuran bereaksiseluruhnya dan membentuk CCMO pada suhu 850�C. Hasil ini menunjukkan peran penting suhu sintering pada sifat�sik dan listrik pada CCMO. Analisis mikrostruktur menunjukkan adanya hubungan penggabungan yang kuat antarbulir yang jelas terlihat pada suhu 1090�C selama 24 jam. Proses ini meningkatkan kepadatan pellet yang disinterdan menunjukkan pembentukan aliran konduksi baru dan pengurangan daerah efektif antar bulir untuk arus transportmelalui sifat resistivitas. Pengamatan dengan SEM juga menunjukkan adanya pengurangan porositas mikrostrukturketika suhu dinaikkan bervariasi dari 36,6% menjadi 0,5%. Sementara resitivitas CCMO menurun dari 18; 1� 103 �mmenjadi 7; 96� 103 �m dengan adanya peningkatan suhu sintering.Kata kunci: CCMO, reaksi fasa solid, suhu sintering, resitivitas

Abstract: The synthesis of CaCu3Mn4O12 (CCMO) has been accomplished via solid-state reaction. Commercialoxides namely calcium carbonate, copper oxide and manganese oxide were used to prepare CCMO. The carbonate andoxides were weighed accordingly to stoichiometric ratios and mixed thoroughly via ball milling for 1 hour. The mixturewas calcined at 850�C for 12 hours and then sintered at 1000�C, 1050�C, 1070�C and 10900C for 24 hours, respectively.The CCMO formation was con�rmed using X-ray di�raction (XRD). The microstructure analysis was carried out usingscanning electron microscopy (SEM), while bulk density and porosity were measured by Archimedes technique. Thee�ects of sintering temperature on microstructure and electrical properties are reported here. The mixture is fullyreacted to form CCMO at 850�C. The results con�rmed that the crucial role of sintering temperature on physical andelectrical transport properties of CCMO. Microstructural analysis revealed the presence of clean and clear intergrainstrong connectivity at 10900C for the period of 24 hours. This process enhances the physical densi�cation of thesintered pellets promotes the creation of new conduction channels and reduction of intergrain e�ective area for transportcurrent under resistivity properties. SEM observation also revealed that the microstructure becomes less porous whensintering temperature increased which varied from 36.6% to 0.5%. Meanwhile resistivity of CCMO will decreased from18:1� 103 �m to 7:96� 103 �m with the increasing sintering temperature.Keywords: CCMO, solid state reaction, sintering temperature, resistivity

Oktober 2011

1 INTRODUCTION

Recently, the complex perovskite CaCu3Mn4O12[1] has attracted the attention of researches. The

crystal structure of CaCu3Mn4O12[2] has the rare fea-

ture of containing Cu2+ (or other Jahn-Teller transi-tion metal cations, such as Mn3+) at the A positionsof the ABO3 perovskite. This Jahn-Teller cation andCa2+ are 1:3 ordered in a 2a0x 2a0x 2a0 cubic cell ofIm3 symmetry (a0: unit cell of the anistotype).

Perovskite-type (ABO3) doped manganese oxidehave generated a considerable interest because of theirmany electronic, magnetic and structural propertiesand potential applications. Extensive theoretical andexperimental e�orts have been made to understandtheir complicated mechanism [3]. The mixed-valenceoxides can be regarded as solid solutions between endmembers such as LaMnO3 with formal valence statesLa3+ Mn3+ O2�

3 and Ca2+ Mn4+ O2�3 .

In this paper, the synthesis of CaCu3Mn4O12 wasc 2011 FMIPA Universitas Sriwijaya 14405-21

Agus/The Effect of Sintering . . . Jurnal Penelitian Sains 14 4(B) 14405reported state reaction and e�ect of di�erent sinteringtemperature. The characterization of physical proper-ties like density, porosity and microstructure observa-tion and also transport current under resistivity prop-erties are also given.

2 MATERIAL AND METHODSCaCu3Mn4O12 (CCMO) was prepared by mixing sto-ichiometric proportions of CaCO3 (99 + % Aldrich),CuO (99 + % Aldrich) and MnO2 (90-95 %, Merck).The mixed powders were ball milled and then calcinedin air at 850�C with soaking time 12 hours. After cal-cination, the sample were ground to �ne powder andpressed into pellets with pressure of 300 MPa and thensintered in air at 1000�C, 1050�C, 1070�C and 1090�Cfor 24 hours, respectively.After calcinations, the sample was ground to �ne

powder and was determined by X-Ray di�raction(XRD) using a Siemen D5000 X-ray di�ractometerwith a CuK� radiation. The surfaces of the sinteredsamples were investigated by scanning electron mi-croscopy (SEM) was using on a Leo Supra 35VP sys-tem. Density and porosity of the sintered sample weremeasured by the Archimedes method. The resistiv-ity was measured by the conventional four-probe tech-nique on sintered pellets with silver paste as the elec-trical contact.

3 RESULTS AND DISCUSSION3.1 X-Ray analysisThe di�ractograms of CCMO was obtained as shownin Fig. 1. The mixture is fully reacted to form CCMOat 850�C. The di�ractograms shows the presence ofCCMO (ICSD 01-072-0401) with the compound crys-tallizes in a body-centered cubic perovskite-relatedstructure (groups: Im3 ). The peaks are formed atpositions which agree quiet well the values given inICDS (01-072-0401) data (see Table 1).

Gambar 1: XRD pattern on CaCu3Mn4O12 at calcina-tions temperature of 850�C

3.2 Scanning electron microscopeMicrostructure is reported to play a vital role indetermining the properties of electroceramics suchCCMO and BaTiO3 (BTO). There has been misper-ception that sintering parameters is the only factorthat has major in uence on the microstructure devel-opment. However, in actual fact, every single precess-ing step, from as early as starting raw materials selec-tion will contribute to the �nal microstructure devel-oped. These process (e.g. synthesis method, mixingand forming) are indirectly involved compared to sin-tering, but it is equally important in post sinteringmicrostructural development.Fig. 2 shows the SEM micrographs of CCMO frac-

ture surfaces ceramics sintered at di�erent tempera-tures. Obviously, porous microstructure is observedin all these sintering temperature except for sinteringtemperature at 1090�C. In Fig.2(a,b), extremely highporosity microstructures are shown in sintered pelletat 1000�C and 1050�C, respectively. It can be ob-served that sintering had just begun in the compactedpellets.The temperature of 1070�C used for sintering is

rather high to caused densi�cation (Fig.2(c)). The in-crease of sintering temperature signi�cantly promotesthe grain growth and microstructural densi�cation.High sintering temperature facilitate grain growth andtherefore produced sharp shrinkage in the specimensintered at 1090�C show in Fig.2(d).

3.3 Bulk density and porosity analysisThe in uence of sintering temperature on the den-sity and porosity value shows in Figs.3 and 4, re-spectively. Density of the CCMO was increased withincreasing sintering temperatures. Theoretically, thedensity of CCMO is 5.62 g/cm3. The highest densitywas recorded for sample sintered at 1090�C with 4.99g/cm3 and the lowest is at 1000�C with 3.43 g/cm3.In theory, the porosity was inversely proportion to

bulk density value. E�ect of sintering temperature toporosity of CCMO is shown in Fig.4 Sample sinteredat 10900C gave the lowest porosity i.e 0.5% compareto the sample sintered at 1000�C with 36.6%. Theseobservations are con�rmed by SEM analysis as givenin Fig.2.

3.4 Linear expansionSince the samples have been sintered in normal atmo-sphere, it is observed that the thickness and diameterof the samples of CCMO quiet homogenous. Linear ex-pansion test is a measurement of the dimension changebefore and after sintering. Comparison of the changein thickness and diameter (mm) for di�erent sintering

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Agus/The Effect of Sintering . . . Jurnal Penelitian Sains 14 4(B) 14405Tabel 1: XRD pattern for CaCu3Mn4O12 from ICSD (01-072-0401)

2�ICSD (01-072-0401) data 17.3 30.2 35.0 39.3 43.2 46.9 50.4 62.8Present work (8500C) 18.9 30.4 35.6 38.8 43.1 48.7 49.9 63.2

Gambar 2: SEM micrograph showing fracture of CCMO in di�erent sintering temperature (a) 1000�C, (b) 1050�C (c)1070�C and (d) 1090�C

Gambar 3: E�ect of sintering temperature on density

temperatures of CCMO is shown in Fig.5. The thick-ness expended 6.54% to 14.54%. While, for diame-ter, 3.34% to 15.93%. It can be explained that duringsintering the pores tended to spheroidise. Hence onheating, the pores shrank in the direction perpendic-ular to the pressing direction, leading to a di�erentdimensional change for both directions.

Gambar 4: E�ect of sintering temperature on porosity

3.5 Electrical characterizationThe resistivity (�) was calculated using the formula� = RA=l (where, R is resistance , A is sample crosssectional area and l is the sample length). It is ob-served that the resistivity measured at four di�erentsintering temperatures for CCMO sample.The resistivity decreased with increasing of sinter-

ing temperature. It is notable that the microstruc-14405-23

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Gambar 5: E�ect of di�erent sintering time on thicknessand diameter change

tural evolution with sintering temperatures corre-sponds well to the variations of the conduction proper-ties of CCMO or other ceramic [4]. The increase of sin-tering temperature promotes the microstructural den-si�cation. It bene�ts the conduction of electric carriersand is thus responsible for the improvement of the con-ductivity. With the increasing of sintering tempera-ture, the grain size and mechanical connection betweengrains are expected to play an important role in theelectronic conduction. It is known that the resistivityis mostly in uenced by the presence of grain boundarywhich acts as region of enhanced scattering for the con-duction electrons. The higher sintering temperaturewill e�ecting to more shrinkage and hence leads to theincreasing of density. This is because sintering reducesthe total pore surface and pore volume. However thefact remained that for CaCu3Mn4O12 (CCMO) sin-tered at 1000�C, 1050�C, 1070�C and 1090�C the re-sistivity is higher than previous reported [5].

Gambar 6: Sintering temperature dependence of the re-sistivity for CaCu3Mn4O12

4 CONCLUSION

Single phase CaCu3Mn4O12 (CCMO) with a per-ovskite -related structure was synthesized by solid-state reaction at calcinations temperature of 8500C.This process enhances the physical densi�cation ofthe sintered pellets promotes the creation of new con-duction channels and reduction of intergrain e�ec-tive area for transport current under resistivity prop-erties. SEM observation also revealed that the mi-crostructure becomes less porous when sintering tem-perature increased which varied from 36.6% to 0.5%.Meanwhile resistivity of CCMO will decreased from18:1 � 103 �m to 7:96 � 103 �with the increasingsintering temperature. For this reason, the physicaland electrical properties are greatly a�ected by sin-tering temperature. It is important to adjust the sin-tering temperature to get appropriate properties forroom temperature applications.

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