Crystal structure refinement, optical properties, dielectric response, and impedance spectroscopy of Ni2+-Co2+ substituted bismuth copper titanate (BCTO)

https://doi.org/10.1016/j.matchemphys.2020.122933Get rights and content

Highlights

  • Crystal structure refinement via Ritveld refinement using Full proof software.

  • Influence of Ni2+-Co2+ doping on the dielectric response of bismuth copper titanate.

  • Impedance and modulus spectroscopy of bismuth copper titanate.

  • Band gap and Urbach energy of bismuth copper titanate.

Abstract

We have synthesized single phase Ni+2-Co+2 substituted bismuth copper titanate (Bi2/3Cu3Ti4O12) electroceramic using the sol-gel autocombustion method. The XRD patterns reveal that the prepared BCTO electroceramic are of single phase without the presence of any other phases such as CuO or TiO2. FESEM micrographs show particles with well-defined cubic shape of bismuth copper titanate ceramics. EDX spectra shows all the chemical elements of the prepared composition, this confirm the stoichiometry and the purity of the synthesized electroceramic. The optical band gap study was carried out using UV–Vis–NIR spectroscopy in the region 225–1000 nm and the highest value of 3.63 eV was observed in the sample having x = 0.1. The dielectric response and impedance spectroscopy of the electroceramic were discussed based on Debye-type relaxation process and Maxwell-Wagner model. The sample having x = 0.0 shows the highest dielectric constant (3800) at room-temperature and a frequency of 42 Hz as compared to x = 0.1 and x = 0.2. The Cole-Cole plots of complex impedance and complex electric modulus indicate that grain-boundary resistance is the major contributor to the dielectric response of the prepared BCTO electroceramic.

Introduction

Decades of considerable attention has been given to the synthesis and characterization of nanomaterials because of the need to produce efficient and portable electronics devices [[1], [2], [3], [4], [5], [6]]. The discovery of the perovskite material calcium copper titanate (CCTO) having chemical composition CaCu3Ti4O12 and giant dielectric constant by Subramanian et al., in 2000 has prompted renewed interest in materials with giant dielectric constant [7]. This is as a result of the fact that advancement in miniaturization of electronics devices, supercapacitors, actuators, catalysis and memory devices requires nanomaterials with giant dielectric constant greater than 1000 [[8], [9], [10], [11], [12]]. Unlike ferroelectric materials such as barium titanate (BaTiO3), CCTO do not show ferroelectric properties even though they exhibit giant dielectric constant (ε104 for polycrystalline and ε105 for single crystals) from 100 to 600 K in the kilohertz region [[13], [14], [15]]. Although the internal barrier layer capacitance (IBLC) model is commonly accepted as the origin of the giant dielectric constant observed in CCTO ceramic, the origin of the giant dielectric constant of this perovskite material has remained a subject of debate among the scientific community [16]. This is further supported by impedance spectroscopy where the perovskite material was observed to exhibit scenario where insulating grain boundaries separates the semiconducting grains, similar to single-step internal barrier layer capacitor [17]. Additionally, transmission electron microscopy (TEM) micrographs and nonlinear current-voltage behaviour of CCTO indicates that the electrical properties of CCTO are greatly influenced by grain boundaries [18].

Bismuth copper titanate (BCTO) (Bi2/3Cu3Ti4O12) as a member of the titanate family with general formula ACu3Ti4O12 (where A = Ba, Ca, Sr, Gd2/3, Pr2/3, Y2/3, Bi2/3 or La2/3) has been rarely explored. Although some researchers have attempted to synthesized BCTO [[19], [20], [21]], the challenge of obtaining giant dielectric constant while maintaining reasonable low dielectric loss still remains an issue [22]. L. Yang et al. employ solid state reaction method and synthesized BCTO, high dielectric constant of approximately 3.3 × 10 5 at 1 kHz was obtained [23]. P. Gautam et al. observed a dielectric constant value of 13.94 × 103 and dielectric loss of approximately 2.4 at 503 K in a Bi2/3Cu3Ti4O12/Bi3LaTi3O12 nanocomposite [24]. P. Gautam et al. synthesize BCTO electroceramic via semi-wet route, the prepared samples shows dielectric constant value of 2.9 × 104 and dielectric loss above 10 [25]. However, these values of the dielectric losses are very high for practical application. In this research, we report on the influence of Ni2+-Co2+ substitution on the properties of BCTO electroceramic prepared using sol-gel autocombustion method. The prepared BCTO electroceramic were characterized via XRD, FTIR, FESEM/EDX, UV–vis NIR spectroscopy and LCR meter.

Section snippets

Experimental details

Sol-gel autocombustion method was used to prepare Bi2/3Cu3-2xNixCoxTi4O12 (x = 0.0, 0.1, 0.2) using high purity (99%–99.5%) AR grade starting material such as Bi(NO3)3·5H2O (CDH), Ni(NO3)2·6H2O (LOBA Chemie), Cu(NO3)2·3H2O (LOBA Chemie), Co(NO3)2·6H2O (LOBA Chemie), TiO2 (LOBA Chemie) and C6H8O7 (LOBA Chemie). Required amount of the starting material in stoichiometric ratios were dissolved in double distilled water to form an aqueous solution, citric acid was added as fuel to the aqueous

Characterization techniques

The structural and phase analysis of the prepared samples was carried out using X-ray diffraction pattern recorded using Bruker AXS D8 advance diffractometer having Cu–Kα radiation in the range 20°–80°. Investigation of attached functional groups and characteristics signature of the prepared BCTO electroceramic was carried out in the range 4000–400 cm−1 using FTIR spectrophotometer (Nicolet FTIR model-8400S) by preparing thin pellets of KBr with the prepared samples in the ratio 10:1

Structural and phase analysis

Fig. 1 shows the XRD patterns of Bi2/3Cu3-2xNixCoxTi4O12 (x = 0.0, 0.1, 0.2) calcined at 900 ̊C for 7 h. The observed peaks in the XRD spectra have been indexed according to standard data (JCPDS card: 80–1343), it was found that the prepared samples are of a single phase with perovskite structure and space group Im-3 with the absence of secondary phase such as CuO, Cu2O, or TiO2 and other related oxides [14]. The lack of secondary phase in the XRD spectra indicates that the substituted cations

Conclusion

Ni2+-Co2+ substituted Bi2/3Cu3Ti4O12 electroceramic have been successfully synthesized using sol-gel autocombustion method. The prepared electroceramics were subjected to various characterizations and subsequent data analysis using different software, the following observations have been made.

  • 1.

    The XRD spectra of the prepared electroceramic show explicit peaks of BCTO electroceramic with single crystalline phase, cubic perovskite structure and space group Im-3. CuO and TiO2 secondary phases have

Author credit statement

Tchouank Tekou Carol T., J. Mohammed, and A. K. Srivastava performed the experiment and discussion of the data.

Sanjay Mishra participated in the calculations and fitting of the data.

Sachin Kumar performed the XRD characterization.

Richa Bhargava and Shakeel Khan performed the dielectric characterization and contributed to the analysis of the dielectric data.

Declaration of competing interest

The authors declare no conflict of interest.

Acknowledgement

The authors would like to thank Materials Research Centre, Malaviya National Institute of Technology, Jaipur, India, for FESEM/EDX characterization and Sophisticated Test and Instrumentation and Centre, Cochin University of Science and Technology, Kerala, India, for UV–vis–near IR spectroscopy characterization.

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