Structural and Dielectric Properties of Mg(1-x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials

Mechanics, Materials Science & Engineering, March 2017

ISSN 2412-5954

Structural and Dielectric Properties of Mg (1-x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials4 V. Sharon Samyuktha 1, T. Subba Rao 2, R. Padma Suvarna1 1

JNTUA, Anantapuram, Andhra Pradesh, India-515001

2

Sri Krishna Devaraya University, Andhra Pradesh, India-515003 DOI 10.2412/mmse.30.345.847 provided by Seo4U.link

Keywords: calcium magnesium titanate, solid state reaction method, dielectric response, XRD.

ABSTRACT. Calcium Magnesium titanate ceramic materials with the molar formula Mg(1-x) CaxTiO3 in which the x varies from 0.7 to 0.8 were synthesized by conventional Solid State Reaction method. The XRD pattern revealed that the samples exhibit Orthorhombic structure. The microstructure and surface morphology for the samples was studied by SEM. The elemental composition was studied by EDAX. The dielectric response of both samples was measured by HIOKI 3532-50 LCR HiTESTER in the frequency range of 1KHz-1MHz from room temperature to 350 0C. These samples find applications in capacitors, microwave antennas, stainless steel electrodes and data storage devices.

Introduction. Over more than 200 years, Ceramic materials are known for technical applications. To overcome the limitations of other conventional materials, various special tailored ceramics are developed with novel chemical, electrical, biological and mechanical properties. In the last three decades there has been a phenomenal transformation in microwave communication systems such as mobile telecommunication systems, satellite communication and broadcasting systems, and global positioning systems. The rapid development in microwave communication systems was made possible with the use of dielectric ceramics as enabling materials for resonators, filters and other key components in microwave components. For these applications the ceramic materials are required to have a high relative permittivity ( r), low dielectric loss, and near zero temperature coefficient of resonant frequency ( f). The combination of these requirements greatly restricts the ceramic dielectrics available for applications in microwave systems [1].

Magnesium titanate ceramics play an important role in microwave technologies such as global positioning system operating at microwave frequencies, resonators, filters, antennas for communication system and multilayer capacitors [2-5]. It is a multifaceted material of low dielectric loss with high quality factor (Q above 20000 at 8GHz) and intermediate dielectric constant ( r=17) [6]. Calcium titanate is a popular ceramic material which has a wide range of applications in industry and technology. The Calcium titanate ceramic material has high dielectric constant ( r=170) Qxf 0 C [7] and modest dielectric losses which makes it a f suitable candidate for microwave applications.

In the present work, the magnesium calcium titanate ceramic materials of different compositions such as Mg(1-x)CaxTiO3 (x=0.7-0.8) were synthesized by conventional Solid State diffusion method and the phase, crystallite size, microstructure and dielectric properties were investigated.

Experimental Procedure. MCT CaxMg(1-x)TiO3 (x=0.7&0.8) was synthesized using Solid- state reaction method. High purity materials such as CaO (99.6% purity, Sigma Aldrich), TiO2 (99.4% purity, Sigma Aldrich), and MgO (99.6% purity, Sigma Aldrich) were used as precursor materials.

These materials were weighed, taken according to the composition and mixed uniformly. The mixed 4

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Mechanics, Materials Science & Engineering, March 2017

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powders were milled for 12h in a Bill Miller (Retsch PM 200). The ground mixtures were dried and placed in alumina crucibles calcined at 1100-11200C for 36h in air in a programmable furnace. Thus obtained calcined powders were again milled for 10h and were pressed into pellets by adding PVA binder and by applying pressure of 8 ton using Hydraulic press. These readily formed pellets were sintered at a temperature of 1200-12500C for 4h in the furnace with a heating rate of 100C/min and then cooled to room temperature.

X-Ray diffractometer (Rigaku), using CuK radiation was used to identify the crystalline phase of the samples. Microstructural analysis of the sintered samples was performed by SEM (Hitachi: S4700) and Energy Dispersive X-Ray Spectroscopy (EDAX) for elemental composition. The dielectric constant and dielectric loss were measured by LCR meter HIOKI 3252-50 in the frequency range 1KHz to 1MHz. The dielectric constant was calculated by [8]:

(1)

where C is capacitance of the pellet; d

is thickness of the pellet;

A is the area of the cross section of the pellet; is the permittivity of free space.

Results and Discussion.

XRD Analysis: The XRD profiles have shown that the sample sintered at 1150 displayed well-defined features is shown in fig. 1. XRD peaks are in good agreement with the (ICDD#22-0153) confirming the Orthorhombic structure. The maximum intensity peak occurs at 330

Fig. 1. XRD pattern for Mg(1-x)CaxTiO3 (x=0,0.7 & 0.8) Ceramic Materials.

The lattice parameters of the samples CaxMg(1-x)TiO3 (x=0.7&0.8) are tabulated in table 1. The average crystalline size (Dp ) is obtained using Scherer formula [9] MMSE Journal. Open Access www.mmse.xyz

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Mechanics, Materials Science & Engineering, March 2017

Dp =

ISSN 2412-5954

/

(3)

where k is a constant and is equal to 0.9; is diffraction angle, is full width half maxima.

Table 1. Lattice parameters of CaxMg(1-x)TiO3 (x=0.7, 0.8) samples.

Compound

Crystal System

a(A0)

b(A0)

c(A0)

Vol(A0)3

CaTiO3

Orthorhombic

5.386

5.444

7.660

224.49

Ca0.2Mg0.8TiO3

Orthorhombic

5.381

5.440

7.652

224.08

Ca0.3Mg0.7TiO3

Orthorhombic

5.386

5.444

7.660

224.67

The dislocation density ( ) of the samples is calculated by the formula =D-2 (m-2) and avg. Crystalline size are also tabulated in the table 2.

Table 2. Average Crystalline size and Dislocation Density.

Sample Name

Average Crystalline size(nm)

Dislocation Density (m -2)

Ca0.2Mg0.8TiO3

48.54

4.244x1014

Ca0.3Mg0.7TiO3

53.58

3.483 x1014

Surface Morphology: The surface morphology is studied by Scanning Electron Microscopy (SEM).

Fig. 2 shows SEM images of CaxMg(1-x)TiO3 (x=0.7, 0.8) which have been made at two different spots grains are almost spherical in shape containing homogeneous distribution containing with distinguished boundaries with less porosity have been observed. The average grain size for the CaxMg(1-x)TiO3 (x=0.7, 0.8) samples was determined to be 5-

Average grain size=

where L

is total test line length;

M the magnification; N the total number of intercepts which the grain boundary makes with the line.

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(4)

Mechanics, Materials Science & Engineering, March 2017

ISSN 2412-5954

a)

b)

Fig. 2. SEM images of a)Mg0.3Ca0.7TiO3 and b)Mg0.2Ca0.8TiO3 ceramic samples.

a)

b)

Fig. 3. EDAX images of a) Mg0.3Ca0.7TiO3 and b)Mg0.2Ca0.8TiO3 ceramic samples.

EDAX: EDAX was performed to determine the concentrations of elements such as Mg, Ca, Ti and O present in the ceramic samples. Fig.3 gives the At% and Wt% of various elements.

Dielectric Properties. The dielectric properties of the sintered ceramic samples of Magnesium Calcium titanate CaxMg(1-x)TiO3 (x=0.7, 0.8) are studied in the temperature range from room temperature to 3500C of varying frequency of 1KHz to 1MHz are depicted in fig. 4-5. At low frequencies, the increase in dielectric constant with temperature was due to accumulation of charge at the grain boundary and at the interface of the electrode sample and the electrode, which was called Space Charge Polarization [11]. As the frequency increased dielectric constant decreases due to gradual diminishing of the space charge polarization, indicating the ionic contribution. The dielectric constant is almost stable with temperature but at high temperature its value increased.

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Fig. 4. Variation of Dielectric constant with Fig. 5. Variation of Dielectric constant with Temperature at different frequencies for Temperature at different frequencies for Mg0.2Ca0.8TiO3 ceramic sample.

Mg0.3Ca0.7TiO3 ceramic sample.

The variation of dielectric loss of the sintered samples CaxMg(1-x)TiO3 (x=0.7, 0.8) with temperature at different frequencies were shown in the fig. 5-6. At low frequency there is increase in dielectric loss with temperature nearly at 2000C and then decreases. At higher frequencies the dielectric loss is very low and almost stable. This may be an extrinsic loss dominated by secondary phases, oxygen vacancies, grain sizes and densification.

Fig. 6. Variation of Dielectric Loss with Fig. 7. Variation of Dielectric Loss with Temperature at different frequencies for Temperature at different frequencies for Mg0.3Ca0.7TiO3 ceramic sample.

Mg0.2Ca0.8TiO3 ceramic sample.

Summary. The XRD confirmed the formation of Calcium Magnesium titanate and is of Orthorhombic structure. The SEM images describe the uniform distribution of grains. EDAX confirms the presence of elements of Mg, Ca, Ti and O. The dielectric constant increases with temperature at low frequencies for both the samples and at high frequencies it value is almost constant with temperature. At 1MHz frequency for both the samples exhibit very low dielectric loss which these suggest that these materials can be used in microwave applications.

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[2] C.L. Huang, et al., Mater. Res. Bull. 37(2002) 2483-2490.

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Cite the paper Sharon Samyuktha, T. Subba Rao, R. Padma Suvarna (2017). Structural and Dielectric Properties of Mg(1x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials. Mechanics, Materials Science & Engineering, Vol 8. doi:10.2412/mmse.30.345.847

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