Elsevier

Ceramics International

Volume 38, Issue 7, September 2012, Pages 5683-5690
Ceramics International

Optical and structural properties of X-doped (X = Mn, Mg, and Zn) PZT nanoparticles by Kramers–Kronig and size strain plot methods

https://doi.org/10.1016/j.ceramint.2012.04.012Get rights and content

Abstract

Pure and X doped (X = Mg, Mn, and Zn) lead zirconate titanate nanoparticles (PZT-NPs) were synthesized using sol-combustion method. The xerogel was calcined at temperature of 700 °C for 2 h. The structure of the prepared powders is characterized using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The XRD results show that the PZT-NPs are formed in perovskite structure with rhombohedral phase. In addition, a small shift was detected in XRD patterns of doped PZT-NPs. Also, the XRD results were analyzed using size strain plot (SSP) to calculate the lattice strain of the prepared samples, which revealed that the lattice strain depends on the different ionic radii of the dopants. To have a better understanding of the optical properties of the pure and doped PZT-NPs, the obtained FTIR spectra were analyzed using Kramers–Kronig method. The results show that there are certain relations between the optical parameters and the wavelength of the incident beam as well as the optical modes. Also, the value of the pure and doped PZT-NPs optical band gaps were estimated using ultra violet and visible (UV–vis) spectroscopy. It was found that the optical properties of the doped samples depend strongly on dopants.

Introduction

In the past few decades, piezoelectric materials because of their various interesting properties have been extensively used in different branches of science and technology including medicine, electronics, military, and oil industries. Lead zirconate titanate (PZT) is an important class of piezoelectric and ferroelectric materials having unique properties [1], PZT is used for fabricating many electronic and optoelectronic devices such as sensors [2], capacitors [3], random access memories (RAM) [4], optical modulators and waveguides [5]. It has been found that the nano structure of PZTs have more interesting properties, so different physical and chemical methods have been developed to prepare of nano-sized PZT powders such as, sol–gel [6], [7], sol-combustion [8], hydrothermal [9], solvothermal [10], precipitation [11], and solid state reactions [12].

Many factors such as solvent [13] and dopant [14] can affect the optical properties of PZT. Therefore, they can be used to control the properties of the PZTs. In addition, the crystal defects affect the optical properties of these materials. Furthermore, doping causes some strain in crystal lattice, which changes the optical and physical properties of the materials [15]. Lattice strain is a measure of the distribution of lattice constants arising from crystal imperfections, such as lattice dislocations due to different ionic radii of dopants comparing to the matrix ions. Both lattice strain (due to the dopant) and crystallite size affect the 2θ peak position, intensity, and broadening of the Bragg peaks, Fig. 1. The crystallite size derived from the peak widths varies as 1/cos θ, whereas strain varies as tan θ [16]. There are some methods to calculate the strain and the crystallite size considering the lattice strain [6]. Size strain plot (SSP) method is used to calculate the crystallite size and its strain [16]. In this method, it is “crystallite size” profile is described by a Lorentzian function and the “strain profile” by a Gaussian function [17]. Fourier transform infrared (FTIR) spectroscopy is a suitable technique to study the optical properties of both inorganic and organic materials in which some mathematical methods are used for the analysis of obtained IR spectra. The most famous mathematical method that has been used widely is Kramers–Kronig (K–K).

In this work, the pure and X-doped PZT-NPs (X = Mn, Mg, and Zn) were prepared by modified sol-combustion method. These dopants were chosen because of their different ionic radii comparing to Ti, to investigate the effect of occurred strain on the optical and structural properties of PZT-NPs, (rZn and rMg >rTi > rMn) by SSP and K–K, respectively. In addition, the values of the optical band gap of the samples have been estimated using UV–vis spectra.

Section snippets

Experimental

To prepare pure PZT-NPs, the starting materials were chosen according to Pb(Zr0.52,Ti0.48)O3 compound. First, a solution of citric and nitric acids were prepared, by dissolving citric acid in minimum water needed and then adding the nitric acid to the citric acid solution at room temperature. After that, the titanium iso-propoxide was added to the solution and stirred to get a clear solution. The amounts of the acids used were selected as below:Citric-acidMetal-cation=2.5andCitric-acid

X-ray diffraction analysis

The XRD patterns of the pure and doped PZT compounds are shown in Fig. 2. All the peaks are related to rhombohedral phase and prove the formation of the PZT in perovskite structure after calcination process at 700 °C for 2 h. No extra peaks, related to the dopants, are detected. The crystallite size of the powders are estimated by Scherrer's equation using (1 1 0) peak. The crystallite size of the pure and doped PZT is presented in Table 1. A small shift is observed for (1 1 0) peak of the doped

Conclusion

Pure and X-doped (X = Mg, Mn, and Zn) PZT-NPs were successfully prepared by sol-combustion method at calcination temperature of 700 °C. The prepared materials were characterized and investigated using XRD, FTIR, UV–vis, TEM, and EDX techniques. XRD results showed that the PZT-NPs are formed in perovskite structure with good crystallity and the crystalline sizes were found to be 94, 90, 65, 100 nm for pure and Zn, Mg, and Mn doped PZT-NPs, respectively. Phonon vibration modes of the samples were

Acknowledgment

This work was suppurated by Ferdowsi University of Mashhad (Vice president for research and technology).

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