Investigation of the Impact of Magnesium Doping on the Structural and Dielectric Properties of the Compound: (Na0.5Bi0.5)1-xMgx[(Ti0.8Zr0.2)0.9(Nb2/3Zn1/3)0.1]O3 (NBMTZNZ)
Ouahab Zakaria* | Bounab Karima | Necira Zoulikha
© 2022 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
OPEN ACCESS
Our research is based on the production of BNT ceramics, abbreviated as NBMTZNZ. And study its structural and electrical properties. Using x-rays, electronic scanning, and non-electrical measurements, we analyzed the samples. The results obtained are of considerable value, allowing them to be exploited to develop the use of our compound.
BNT, perovskite, DRX, SEM, molten salt, dielectric
Inorganic compounds made by metals or semi-metals with non-metallic elements are called ceramics. A wide range of inorganic materials contains materials such as clay, sand and feldspar [1]. The abundance of raw materials has a lot of advantages such as: easy processing, simple manufacturing, relatively low cost and easy of use etc. Using the ceramics is increased with reasons of hardness, heat resistance [2]. Ceramics are typically produced by forming ceramic particles in to a desired shape and applying heating a process known as firing. Optimization of the forming process can require multiple rounds so forming and firing to fine-tune the forming conditions. However, conventional firing is highly energy-intensive [3, 4]. Ceramics are classified as inorganic and non-metallic materials that are essential to our daily life style. Ceramic and materials engineers are the people who design the processes in which these products can be made, create new types of ceramic products, and find different uses for ceramic products in everyday life. The properties of ceramic materials, like all materials, are dictated by the types of atoms present, the types of bonding between the atoms, and the way the atoms are packed together. This is known as the atomics cale structure. Most ceramics are made up of two or more elements. This is called a compound. For example, alumina (Al2O3), is a compound made up of aluminium atoms and oxygen atoms. The atoms in ceramic materials are held to gather by a chemical bond. The two most common chemical bonds for ceramic materials are covalent and ionic. For metals, the chemical bond is called them etallic bond. The bonding of atoms together is much stronger in covalent and ionic bonding than in metallic. That is why, generally speaking, metals are ductile and ceramics are brittle. Due to ceramic materials wide range of properties, they are used for a multitude of applications. In general, most ceramics are: hard, wear-resistant, brittle, refractory, the malinsulators, electrical insulators, nonmagnetic, oxidationres istant, prone to the rmalshock, and chemically stable. Ceramics have replaced metals in most of the tribological application because it has higher hardness, good thermals t ability at a higher temperature and better wear resistance etc. To improve the performance and life of the ceramics, the or etical and practical investigation of its characteristics are essential. The Tribological behavior of ceramics is a complex phenomenon on and requires added efforts to develop better understanding. The wear of material is influenced by applied load, sliding speed, surrounding temperature, time of contact, touching geometry, lubrication and its chemistry, material surface characteristics such as composition as well as roughness and the amount of oxygen present. Many works were one to study the wear characteristics of ceramics. Lead-containing ferroelectric materials such as Pb (Zr1-xTix) O3 (PZT) based ceramics (together with other toxic materials), have been widely used in numerous technological applications due to their excellent piezoelectric properties. However, the rapid growing amount of electronic residues and it’s in correct elimination is becoming a major environmental problem. A consequence of this global issue, since 2003 the European Union included the PZT in its legislation, joint with other danger ous substances that’s should be replaced with safe materials [5]. The dielectric ceramics Pb (Zr,Ti)O3, abbreviated (PZT) are very sensitive oxides to insert ion or substitute ion at site A(and/or) site B, because of their simple perovskite ABO3 structure. The purpose of doping is often related to the improvement of ceramic properties for their industrial applications (sensors, actuators and resonators) [2]. Lead-containing ferroelectric materials such as Pb (Zr, Ti) O3(PZT) and PZT-based [6, 7]. Multi-component ceramics have been extensively utilized as sensors, actuators and ultrasonic transducers in various electronics due toits excellent piezoelectric properties. However, Problems with the vaporization of PbO during the sintering process and treatment of Pb-containing products cause critical environmental pollution. Recently, much greater consideration has been given to the study of lead-free piezoelectric materials for the replacement of lead-containing ferroelectrics [6, 7]. Bi0.5Na0.5TiO3(BNT)-based as typical RFEs materials have recently gained a lot of attention because of their huge Pmax(>40C/cm2) and high Curie temperature (Tc320℃) [8]. Some success full strategies, such as A/B site doping and concurrent substitution of A and Bsites, have been proven to improve the quality of BNT-based ceramics [9, 10]. Bi0.5Na0.5TiO3(BNT) is a ferroelectric with Bi3+ and Na+ occupy the A site in the perovskite phase [11, 12]. The Na0.5Bi0.5TiO3(NBT) and NBT based system with ABO3 (where A=mono or divalent ions, B=tri, tetra or pentavalent ions) [13,14]. Perovskite structure is one of the principal lead-free materials [15, 16]. This work concentrates on material derived from BNT and exempted lead. The goal of this work is to synthesize the solution NBMTZNZ. We analyze the structural and dielectric characterization of these doped BNT materials. We synthesized the solid solution NBMTZNZ (such as x=0,0.02). We will try to determine the impact of variation in the value of x (which is primarily connected to the amount of magnesium in our ceramics) on the structural and dielectric properties.
2.1 Samples preparation
The ceramics (Na0,5Bi0,5) [(Ti0.8Zr0.2)0,9(Zn1/3Nb2/3)0,1] O3 and (Na0,5Bi0,5)0,98Mg0,02[(Ti0.8 Zr0.2)0.9(Zn1/3 Nb2/3)0.1] O3 are prepared by molten salt method (MS). Reagent-grade Bi2O3 (99.0%), Na2CO3 (99 ,5%), TiO2 (99,0%), ZrO2(99,0%), ZnO (99,5%), Nb2O5 (99,99%) and MgO (99,0%) were weighted according to the stoichiometric ratio and mixed together at the same weight (NaCl/KCl) (1/1). Then, the mixture was crushed in a mortar of a glass for 3 hours and calcined at 900°C for 4 hours with a heating rate of 2°C/min to assure that remaining salts were removed. The goal of regrinding is to minimize agglomerates created during the calcination process, homogenize the powder, and boost its reactivity. After regrinding, the powder is compacted into pellets with a mass of 1,5 g and a diameter of around 13 mm. Natural sintering under air is used to sinter our ceramics in an alumina crucible at 1150°C. Temperature increases to the defined temperature with a speed of 2°C/min. Then, it stabilizes for 4-hour. Finally, it decreases to ambient.
2.2 Material characterization
The spectra of our sintered ceramics are created at room temperature using a vertical diffractometer «BRUKER-AXE type D8» located in the University of Biskra's X-ray laboratory. The line profiles were measured using an automatic point-by-point counting system with a 0.02° pitch. All diffraction diagrams are recorded in the angular domain 0° ˂ 2 ˂ 80°, which may be sufficient for the identification of the different phases. We note that we used X’Pert HighScore for the analyzing and indexing the different lines. The micrographs of our samples are performed using a scanning electron microscope of type JEOL JSM-6390lv provided the X-ray laboratory of the University of Biskra. An operating system allows a computer to regulate it. The goal of these micrographs is to study the morphology of our samples. The density of sintered pellets is determined by geometric measurements (diameter and thickness) on each sintered pellet, with the use of a slide palmer. The formula for calculating the density (d) is as follows: $\mathrm{d}=\mathrm{m} / \pi(\theta / 2)^2 \mathrm{e}$. Such as: m: Mass of the pellet (g), θ: and e: Using an LCR meter, the dielectric permittivity and loss tangent of sintered samples were determined as a function of frequency at different temperatures (300 °K to 500 °K).
3.1 DRX
X-ray analysis (Figure1) reveals that the pellet in the synthesis method and crystallinity in the cubic system with space group Pm-3m have the perovskite structure of (ICSD:(01-089-3109) [8, 9]. The lattice parameters were calculated from the XRD data using the cellref program as shown in Table 1.
Figure 1. X-raydiffractogrammes
Table 1. Lattice parameters
|
Parameters |
X |
|
|
0 |
0,02 |
|
|
a(Å) |
3.8822 |
3.9130 |
|
b(Å) |
3.8822 |
3.9130 |
|
c(Å) |
3.8822 |
3.9130 |
|
α |
90° |
90 |
|
β |
90° |
90 |
|
γ |
90° |
90 |
|
Grainsseize(µm) |
4,806 |
4,695 |
Figure 2. SEM micrograph of (Na0.5Bi0.5)[(Ti0.8Zr0.2)0.9(Nb2/3Zn1/3)0,1]O3
3.2 SEM micrograph
Figures 2 and 3 displays scanning electron microscope (SEM) photographs of compositions doped with Mg at 1150°C sintering temperature. At first glance, the samples appear homogeneous. We suggested that the ceramic is dense and the porosity is low [8, 10]. With an increase in composition from 4.806µm for X = 0 to 4.695µm for X = 0.02, the average grain size drops as shown in Table 1. We can say that the molten salt method is suitable for synthesis our material.
Figure 3. SEM micrographs of (Na0.5 Bi0.5)0,98 Mg0,02 [(Ti0.8 Zr0.2)0.9 (Nb2/3Zn1/3)0,1]O3
3.3 Dielectric characterization
The electrical qualities of ceramic samples are related to the dielectric properties: permittivity (ℇr), Resistivity (ρ), Loss tangent (tan δ) and dielectric rigidity [11, 12]. In our work, we concentrated on determining the dielectric constant values and loss tangent values as shown in Figures 4, 5, 6, and 7. It is observed from ℇr vs T plots that ℇr increases with increasing temperature up to certain temperature and shows broad dielectric maxima around a particular temperature, represented as Tm, and it decreases slowly with temperature above Tm. It can be seen that Tm depends on the composition (x), such as Tm=400 for x=0 and 425 for x=0.02 [13]. The curves ℇr(T) exhibit the same beauty, that is, they rise with temperature, reach a maximum, then fall. One can see that the maximum electrical permittivity ℇm values for each composition (x=0 and x=0.02) are noted at 100Hz. As frequency decreases, ℇr increases until it nearly disappears at the highest frequency (100KHz) for two compositions. It has been noticed that the dielectric constant decreases as frequency increases, which can be attributed to the presence of various types of decreasing polarization [14]. The dielectric constant has frequency dependence especially, at the low frequencies(100Hz), which is called the low frequency dielectric dispersion. A strong low-frequency dielectric dispersion has also been observed in NBT which was previously reported [7, 15]. The maximum dielectric constant temperature (Tm) is related to the ferroelectric-paraelectric phase transition temperature. With the increase of frequency, the ℇm values of all samples gradually decrease, which may be ascribed to the fact that the dipole cannot be consistent with the frequency of the electric field. The Tm values move to a high temperature, showing the characteristics of frequency dispersion [16, 17]. This observation indicates a relaxation process which can be related to ferroelectric antiferroelectric phase transition [18, 19]. The factor of dissipation is connected to a rate of electrical energy loss, frequently manifested as dissipated heat [20]. Because the samples had been changed into a paraelectric phase, there was a quick reduction in the electrical loss Tanδ, which in turn reduced the polarization loss. For all samples, Tm moves toward a higher temperature as the frequency increases, indicating the presence of relaxing characteristics [21]. This increase in tanδ may be due to an increase in the electrical conduction of the residual current and absorption current [22, 23]. This increase in tanδ may be due to an increase in the electrical conduction of the residual current and absorption current [24, 25].
Figure 4. Dielectric constant of Na0.5 Bi0.5) [(Ti0.8 Zr0.2)0.9 (Nb2/3Zn1/3)0,1] O3
Figure 5. The dielectric constant of (Na0.5 Bi0.5) 0,98 Mg 0,02 [(Ti0.8 Zr0.2)0.9 (Nb2/3Zn1/3)0,1] O3
Figure 6. Loss tangent of (Na0.5Bi0.5)0,98 [(Ti0.8Zr0.2)0.9 (Nb2/3Zn1/3)0,1] O3 tangent of Na0.5Bi0.5) [(Ti0.8Zr0.2)0.9 (Nb2/3Zn1/3)0,1] O3
Figure 7. Loss tangent of (Na0.5Bi0.5) 0,98 Mg0,02 [(Ti0.8Zr0.2)0.9 (Nb2/3Zn1/3)0,1] O3
The lead free NBMTZNZ ceramics were prepared by using the molten salt synthesis route (MS). The effect of sintering temperature on structural and dielectric properties was investigated. The ceramics were calcined at 900℃ and sintered at 1150℃. X-ray diffraction (XRD) analysis reveals that the NBMTZNZceramics have a perovskite structure, but phase pyrochlore is obtained. The morphological study by SEM analysis confirms that the samples have a relatively dense pure. The results of DRX and SEM confirmed suitability of MS. The dielectric measurements support our findings that a change in Mg values has an impact on the quality of the ceramic that we tested. We noted ℇm is 2650 for x=0 and 3000 for x=0.02 such as TC is 400℃ for x=0 and 425°C for x=0.02. All results considered a hard-ferroelectric material, can be used at law frequencies in several technological fields.
These studies were carried out using the equipment of the laboratory of Applied Chemistry at university of Biskra and the laboratory of engineers physicsat the university of Tiaret.
|
a,b,c |
Lattice parameters in Å |
|
|
D |
Density (g/cm3) |
|
|
e |
Pellet thickness (cm) |
|
|
M |
pellet Masse (g) |
|
|
Tc |
Curie temperature (℃) |
|
|
Tm |
Maximum temperature (℃) |
|
|
Greeks ymbols |
||
|
$\alpha, \beta, \gamma$ |
Mesh angls(°) |
|
|
Ɵ |
Pellet diameter(cm) |
|
|
$\pi$ |
3,14 |
|
|
Subscripts |
||
|
BNT |
Bi0.5Na0.5TiO3 |
|
|
DRX |
X-ray diffractogrammes |
|
|
MS |
Molten salt method |
|
|
SEM |
Scaning elcetronic microscop |
|
|
NBMTZNZ |
(Na0.5Bi0.5)1-xMgx[(Ti0.8Zr0.2)0.9(Nb2/3 Zn1/3)0.1]O3 |
|
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