Perovskite material is a material with chemical formula ABX3-type, which exhibits a similar crystal structure of CaTiO3. In this material, A and B are metal cations with ionic valences combined to +6, e.g., (Li+:Nb5+; Ba2+:Ti4+; Sr2+:Mn4+; La3+:Fe3+) and X is an electronegative anion with ionic valence (−2), such as O2−, S2−, etc. The properties of a perovskite material strongly depend on the synthesis route of materials. The perovskite materials may be oxides (ABO3:CaMnO3), halides (ABX3:X = Cl, Br, I), nitrides (ABN3:CaMoN3), sulfides (ABS3:LaYS3), etc. and they may exist in different forms, such as powders, thin films, etc. There are various routes for the synthesis of several perovskites, such as solid phase synthesis, liquid phase synthesis, gas phase synthesis, etc. In this chapter, we discuss various techniques for the synthesis of oxide perovskites in powder form using solid, liquid and gas phase synthesis methods and we also present an overview on the other type of perovskite materials. The X-ray diffraction, scanning electron microscopy and optical techniques are used to study the purity of crystallographic phase, morphology and photoluminescence properties of the perovskites. Some applications of the perovskite materials are also discussed.
- Rietveld refinement
- FullProf Suite
- lanthanide phosphor
The general chemical formula of a perovskite material is ABX3, which contains a crystal structure similar to CaTiO3. It was initially discovered by German geologist Gustav Rose in 1839 in Ural Mountains, and named after Russian mineralogist Lev Perovski [1, 2]. In ABX3 perovskite, A and B are termed as metal cations having ionic valences combined to +6 e.g., (Li+:Nb5+; Ba2+:Ti4+; Sr2+:Mn4+; La3+:Fe3+) and X is an electronegative anion with ionic valence −2 such as O2−, S2− etc. [3, 4, 5, 6]. The perovskite materials may be oxides, halides, nitrides, sulfides, etc. and they may exist in different forms, such as powders, thin films, etc. [7, 8, 9, 10]. The perovskite material has attracted our attention as it can house up a variety of cations at A- and B-sites individually and/or simultaneously along with anions at X-site [11, 12]. The perovskite materials can be classified in ideal and distorted perovskite materials.
An ideal perovskite material crystallizes into a simple cubic structure with Pmm space group. In the Pmm space group with perovskite structure, A atoms occupy 1(a) site at (0, 0, 0) and B atoms occupy 1(b) site at (1/2, 1/2, 1/2) whereas X atoms occupy 3(c) site at (1/2, 1/2, 0). However, equivalently A, B and X atoms can also occupy 1(a) site at (1/2, 1/2, 1/2), 1(b) site at (0, 0, 0) and 3(c) site at (0, 0, 1/2), respectively, as shown in Figure 1. In this figure, A, B and X are presented in terms of ionic radii [13, 14]. In the unit cell of a perovskite, the cation ‘B’ forms octahedral arrangement with X-anions, i.e., BX6 and the cation ‘A’ occupies cuboctahedral site with X-anions, i.e., AX12.
The family of perovskite material includes numerous types of oxide forms, such as transition metal oxides with the general formula of ABO3. The oxide perovskite materials are widely synthesized and are studied for wide applications in various technological fields. In light of these properties, we describe oxide perovskites in more detail.
Victor Moritz Goldschmidt presented an empirical relationship among the ionic radii of A, B and O, known as tolerance factor (t) to estimate the stability of a perovskite structure. This relation is valid for the relevant ionic radii at room temperature . The numerical value of the tolerance factor can be found by the following Eq. (1):
where the term rA is the ionic radius of cation A and that of rB is ionic radius of B cation, whereas rO is the ionic radius of oxygen anion (O2−). The ionic radius of A cation is always larger than that of the B cation. The tolerance factor provides an idea about the selection of combination of A and B cations in order to prepare an ideal perovskite material. Eq. (1) can also be expressed in other form, which may be valid for any temperature as given by Eq. (2):
where dA-O and dB-O are average bond-lengths between A-O and B-O, respectively .
The distorted perovskite materials are those materials, which crystallize into other than the cubic structures. As far as we know that the perovskite material can accommodate different ions at the A- and B-sites. The variation in the A- and/or B-sites cations causes a variation in the tolerance factor. The variation in tolerance factor leads to a change in the perovskite structure from cubic to non-cubic distorted perovskite structure. For a stable perovskite, the value of tolerance factor should lie in the range of 0.88–1.09 . An ideal perovskite crystal exhibits tolerance factor equal to unity (i.e., t = 1). For t < 1, the perovskite materials show the rhombohedral or monoclinic structure while in the case of t > 1; it reveals tetragonal or orthorhombic structure . Due to distortion in the perovskite system, the BO6 octahedral led tilted from an ideal situation and causes a change/enhancement in unit cell volume. Thus, the tolerance factor is a measure of the extent of distortion in the perovskite structure. Figure 2 shows unit cells for some distorted perovskite structures.
There are two general requirements for the formation of a perovskite material, which are given as:
Electro-neutrality: the chemical formula of perovskite material should have neutral balanced charge; consequently, the sum of total charges at A- and B-sites cations must be equal to total charges at O-site (oxygen) of anion(s). A suitable charge distribution is to be achieved in the forms of A3+B3+O3 or A4+B2+O3 or A1+B5+O3 [14, 19].
The pure perovskite materials (ABO3) do not always provide the desired properties. In order to make them useful, the doping at A- and/or B-sites is required. Doping at A- and/or B-sites improves the properties and also generates very interesting phenomena due to change in crystal structure, bond-lengths, ionic states, etc. The general chemical formula of A- and B-sites after doping in the perovskite matrix may be found in the form of A1−xA’xBO3 (0 < x < 1) and AB1−yB’yO3 (0 < y < 1), respectively. However, the simultaneous A- and B-sites doped oxide perovskites have general formula A1−xA’xB1−yB’yO3. Recently, there are several reports on lanthanide-based rare-earth doped perovskites [21, 22, 23, 24]. Initially, we discuss the synthesis process used for the preparation of rare-earth doped perovskite materials along with phase identification and structural analysis by Rietveld refinement of X-ray diffraction (XRD) patterns.
2. Synthesis techniques for perovskite materials
There are various techniques adopted for synthesis of the perovskite materials. As we know that the properties of the perovskite materials strongly depend on the synthesis routes. Therefore, the synthesis methods are very important factor to get desired properties from the perovskite materials . These synthesis techniques can be divided into three categories:
Solid phase synthesis
Liquid phase synthesis
Gas phase synthesis
2.1 Solid phase synthesis
The solid phase synthesis technique is a widely used for the synthesis of polycrystalline solid perovskite materials from the mixture of solid raw substances. The starting materials do not react to each other at room temperature. When it fires at higher temperatures i.e., 900–1500°C, the reaction occurs at a remarkable rate. The solid phase synthesis technique requires raw materials in the oxide form. It is of two types as discussed below.
2.1.1 Mechanical ball-milling method
It is one of the solid phase synthesis techniques for the preparation of polycrystalline perovskite oxide materials widely used by researchers. This method involves grinding and mixing of raw materials in several times. For the synthesis of any oxide perovskite materials, one has to take stoichiometric amount of metal oxide as starting materials.
Let us discuss the entire process of this method using an example of PbZrxTi1−xO3 (PZT) perovskite. At first, the stoichiometric amounts of PbO, ZrO2, and TiO2 were weighed and grinded in mortar using pestle by hand for 1–2 hours. After hand grinding of the all raw materials, the mixtures were ball milled in a planetary ball milling system to further mixing in the presence of acetone or alcohol as mixing medium for 6–8 hours at a normal round per minute (rpm) of 50–80 in clockwise and anticlockwise directions. After ball milling, the mixtures were dried and divided into several parts for calcination at different temperatures from 900 to 1500°C for 5–24 hours to optimize the pure phase of PZT. The calcined powder of PZT was converted into a pellet form and sintered at a higher temperature than the calcination temperature to get highly dense material . Materials synthesized by this method have particles size in the sub-micrometer range . In this method, one can also use metal carbonates for the synthesis because at ordinary temperature no chemical reaction takes place. Some other rare earth doped R0.5Ba0.5CoO3 (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) perovskites were also synthesized using this method .
2.1.2 High energy ball-milling method
This technique is very similar to that of mechanical ball-milling technique. It is used for the synthesis of nanoparticles of the oxide materials. This method strictly bounds to use only metal oxides for the synthesis because there is possibility of chemical reaction during high energy ball-milling, which may generate different toxic and/or unwanted gases. This technique adopts relatively large rpm from few hundreds to few thousands. This method requires moderately low temperature for the synthesis of materials.
Now, we discuss whole procedures by taking an example of 0.7BiFeO3-0.3PbTiO3 (BF-PT) solid solution . The stoichiometric amounts of highly pure Bi2O3, Fe2O3, PbO and TiO2 were taken as raw materials for the synthesis of BF-PT and were hand mixed using mortar and pestle. The raw materials were then ball-milled for 5–24 hours with zirconia balls in presence of alcohol as mixing media in the 1:10 weight ratio of samples and balls at 500–1000 rpm. The ball mixed material was dried at 90°C and was calcined at different temperatures and the XRD patterns were recorded to check the formation of pure phased samples.
For dielectric measurements, the calcined powder of sample was mixed in 2% aqueous solution of PVA (polyvinyl alcohol) used as binder and a pellet was made. The formed pellet was fired at 500°C for 10 hours to remove the binder and sintered at higher temperatures than the calcination temperature to get the desired highly dense material . One can also use this method for the reduction of particles size from a micrometric scale to nanometric scale. Figure 3 demonstrates flow chart of the synthesis procedures for the preparation of perovskite materials using solid phase method.
2.2 Liquid phase synthesis
The liquid or chemical phase synthesis technique is widely used for the synthesis of nano-sized materials. In this method, the starting materials may react to each other at room temperature. There are various methods for the synthesis of perovskite nano-materials in liquid phase synthesis, such as auto-combustion, sol-gel, co-precipitation, etc. which are summarized below in more detail .
2.2.1 Auto-combustion method
The auto-combustion technique is a very facile and inexpensive method for the preparation of perovskite nano-materials. This method requires raw materials in nitrate and/or acetate forms, which should be easily soluble in distilled water. It also requires an organic fuel, such as glycine, urea or citric acid to help in the combustion process.
Let us consider this process for the synthesis of perovskite material. Kumar et al. synthesized La0.7Sr0.3MnO3 perovskite manganite using highly pure raw materials, such as La2O3, SrCO3, Mn(CH3COO)2.4H2O and glycine, used as fuel in stoichiometric amounts. Firstly, La2O3 and SrCO3 were dissolved in diluted nitric acid to convert into their respective nitrates and then Mn(CH3COO)2.4H2O and glycine were dissolved into distilled water. All the precursor solutions of the raw materials were dissolved/prepared separately and finally they were mixed together under continuous stirring and kept on a magnetic stirrer at 200–225°C . After constant stirring for 4–6 hours, the mixture solution turned thicker and forms gel, with further increase in time, an auto-ignition occurs resulting in flame, and generates huge amount of different gases. Finally, the mixed solution is converted into blackish-brown powder. At the time of combustion, the temperature of whole reaction system may reach up to 800–1000°C for a very short duration . The blackish-brown powder was collected and divided into several parts for the calcination at various temperatures and the optimization of synthesis temperature to prepare a pure phased sample. This results different sized particles of La0.7Sr0.3MnO3 perovskites. The same method is also used to prepare bulk samples of Ba1−xSrxMnO3 perovskites . Figure 4a shows a flow chart of the procedures adopted for the synthesis of perovskite materials using this method .
2.2.2 Sol-gel method
The sol-gel method involves physical and chemical procedures correlated with hydrolysis, condensation, polymerization, gelation, drying and densification . This method also requires starting materials in the form of metal alkoxides. Metal alkoxides have the general chemical formula in the form of M(OR)x, which can be supposed as either a derivative of an alcohol ROH, where R is an alkyl group, in which the hydroxyl proton is substituted by a metal M or a derivative of a metal hydroxide M(OH)x . The metal alkoxides of the desired metals are taken in the stoichiometric amounts and were dissolved in water or in a suitable solvent (say, alcohol) at an ambient temperature of 50–75°C under constant stirring. Controlling the pH value of the metal alkoxides solutions is imperative to keep away from the precipitation and to form the homogeneous gel that can be accomplished by adding acidic or basic solutions. These processes are known as hydrolysis and condensation leading to construction of the polymeric chains.
The formation of polymeric chains ultimately leads to a noticeable improvement in the viscosity of reaction mixture and the creation of a gel. The obtained gel was dried between 150 and 200°C to remove the volatile organic components and excess water, etc. from the gel [35, 36]. After this, to obtain the single phase of the desired sample, the dried gel was calcined at various temperatures in the range of 500–800°C. Andrade et al. synthesized nanotubes and nanoparticles of La0.6Ca0.4MnO3 perovskite manganite using sol-gel method following calcination at different temperatures . They used stoichiometric amounts of La(NO3)3.6H2O, CaCO3 and Mn(CH3COO)2.4H2O for the synthesis of La0.6Ca0.4MnO3 perovskite. The CaCO3 was dissolved into nitric acid to convert into calcium nitrate, while La(NO3)3.6H2O and Mn(CH3COO)2.4H2O were dissolved in distilled water. All the solutions were mixed together. Then a suitable amount of polyethylene glycol (PEG) was added to the precursor solutions used as polymerizing agent.
The final solution was heated at 70°C for 6 hours to complete the polymerization and to evaporate excess amount of solvents from the solution. Finally, the entire solution was converted into yellow viscous gel, which was calcined at different temperatures from 700 to 1000°C. Figure 4b shows a schematic flow chart of the processes involved in the synthesis of perovskite materials using this method.
2.2.3 Co-precipitation method
The co-precipitation method requires starting materials of metal cations from a common medium, which precipitates in the form of carbonates, hydroxides, oxalates or citrates [38, 39, 40, 41]. The obtained precipitates are consequently calcined at different temperatures to get the single phase of the desired product in powder form. Using this method, one can get highly homogeneous powder sample. To achieve highly homogeneous material, the solubility of the products obtained during precipitation of metal cations should be very close to each-other . In co-precipitation process, the mixing of precursor solutions occurs at atomic level, which causes lower particle size of the final product and at very low calcination temperature to get the final product . On the other hand, each synthesis of the material requires its particular conditions and precursor reactions, etc. It is to note that to obtain the ultimate product having desired properties, the co-precipitation method requires to control the pH of solution, concentration, stirring speed and temperature of the mixture .
It can be understood by considering the example of LaMn1−xFexO3 (x = 0, 0.1, 0.2) perovskites synthesized by Geetha et al. . The stoichiometric amounts of La(NO3)3.6H2O, Fe(NO3)3.9H2O and MnCl2.4H2O were dissolved in distilled water. All the precursor solutions were mixed together and stirred continuously at 50°C for 30 minutes. After that, NaOH solution was added slowly until the pH of solution is attained to 13. Then the mixed solution of the precursors was again stirred constantly till the formation of black precipitate. The precipitate was collected and washed many times to remove the chlorides and kept in an oven to dry at 50°C. Thus, the final product was calcined at 800°C for 6 hours.
As we discussed that liquid phase synthesis techniques are used to synthesize nano-crystalline perovskite materials at very low temperature. By using high firing temperature, one can also produce bulk perovskite material, like solid phase synthesis route.
2.3 Gas phase synthesis
Gas phase synthesis technique contains different methods such as flames, furnaces, plasmas and lasers for the synthesis of powder oxide materials. In each method, the kinetics and thermodynamics of the reaction are similar but the designed reactor is different. To get the narrow particle size distribution of the oxide materials using gas phase synthesis, dispersion must be minimized as it leads to an enlargement of the particle size distribution . Using gas phase reactors, one can produce highly pure perovskite powder materials since it is comparatively simple to get purified reactant gases with impurities from the ppm (parts per million) to ppb (parts per billion) level.
Various electronic devices of perovskite materials are fabricated in the form of thin films using gas phase synthesis technique different from the synthesis methods used for perovskite oxides. Several techniques were developed for the preparation of thin films, such as chemical vapor deposition , molecular beam epitaxy , laser ablation , DC sputtering , magnetron sputtering , thermal evaporation  and electron beam evaporation . The gas phase synthesis requires special arrangements and instrumentations for the preparation of good quality of samples with the desired properties. These gas phase methods can be classified into three categories:
Synthesis at the crystallization temperature under an appropriate atmosphere condition temperature.
Synthesis in an intermediate temperature range of 600–800°C and then post-annealing treatment at higher temperatures.
Synthesis at very low substrate temperature and then post-annealing at very high temperature.
3. Structural and optical properties
3.1 Identification of phase purity: X-ray diffraction studies
It is very important to check the phase and purity of the synthesized perovskite materials. Without knowing the phase purity, one cannot come to any conclusion about the properties exhibited by the perovskite materials. The XRD technique is a suitable tool to identify the phase of perovskites. From the XRD data, one can find out relative phase fractions of different phases present in the prepared samples. One can also find out lattice constants, unit cell volume, crystallite size, lattice strain and theoretical density from the XRD pattern. The XRD technique is also used to optimize the synthesis conditions for the perovskite materials. By matching the XRD pattern of the synthesized material with the standard XRD pattern of the cubic phase of CaTiO3 (CT) perovskite, one can conclude about the phase purity, i.e., whether, the perovskite is pure or has some amount of impure phase(s) or crystallizes into distorted perovskite. Figure 5 shows the XRD pattern of the cubic CT perovskite with JCPDS File No. 75-2100 using X-ray radiation of 1.5406 Å. The analysis of XRD pattern gives unit cell lattice parameter a = 3.795 Å and unit cell volume V = 54.656 Å3. An ideal perovskite material displays reflections from all allowed planes of the primitive unit cell. It shows most intense XRD peak for (110) plane in the 2θ range of 32–34° and first singlet reflection corresponding to (100) plane between 22 and 24°. As we know that the different materials display different XRD patterns as like the finger print of the humans. However, a certain prototype of materials gives the XRD pattern in a well-defined manner. In order to make sure that the synthesized sample is perovskite or not, we have to match the XRD pattern of the synthesized sample with the XRD pattern of CT. If it matches it forms a perovskite phase otherwise not.
Figure 6a shows the room-temperature XRD pattern for BaTiO3 (BT) synthesized by mechanical ball-milling method followed by calcination at 950°C for 5 hours and it is compared with XRD pattern of CT. The comparison of both the XRD patterns reveals that the XRD pattern of BT matches with that of the CT. This further confirms that BT is a perovskite material. The Bragg’s peaks in XRD pattern of BT perovskite is shifted towards lower angle side compared to CT. This indicates that the lattice parameters of BT are larger than that of the CT. Furthermore, the Bragg peak around 22° is asymmetric in lower angle side, which shows doublet nature in the peak, i.e., the lattice plane (100) of CT split into (001) and (100) of BT is shown as inset in Figure 6a. Similarly, the other Bragg’s peaks also show asymmetrical behavior. All these observations reveal that the crystal structure of BT is distorted from an ideal perovskite structure. The Rietveld refinement of XRD pattern of BT reveals that the BT crystallizes into tetragonality distorted structure with P4mm space group . It has been also observed that the presence of superlattice reflection(s) in the XRD pattern indicates the formation of distorted perovskite structure from an ideal cubic [54, 55].
The structural analysis of the known or unknown perovskite materials can be identified by Rietveld refinement of the powder XRD pattern with the help of some standard software . Most of researchers use FullProf Suite to identify the structure of various perovskite materials . From Rietveld refinement, one can get lattice parameters, atomic coordinates of the constituent atoms present in the unit cell, average bond-lengths and angles, draw molecular structure to see the surroundings of the A- and B-sites’ cations with anions and many more [33, 58, 59]. One can also find out magnetic structure from the Rietveld refinement of the neutron diffraction data .
We performed the Rietveld refinement of XRD pattern of BT using P4mm space group of the tetragonal structure. In P4mm space group, Ti4+-ions and Ba2+-ions occupy 1(a) site at (0, 0, 0) and 1(b) site at (0.5, 0.5, 0.5 + δz), respectively, while, O2−(1) and O2−(2) anions substitute 1(a) site at (0, 0, 0.5 + δz) and 2(c) site at (0.5, 0, δz), respectively [53, 61]. The structural analysis provides lattice constants a = b = 4.0005(1) Å and c = 4.0255(2) Å and unit cell volume V = 64.423(4) Å3 with tetragonality (c/a) of 1.006 close to the earlier reported value . Figure 6b shows Rietveld fit of the XRD pattern for the BT perovskite. In this figure, the scattered dots are used to present experimental XRD pattern and continuous line over experimental pattern is to show the simulated XRD pattern. Lower continuous curve shows difference between experimental and simulated XRD patterns. The vertical bars represent positions of the Bragg’s reflection. The inset of Figure 6b demonstrates ball and stick molecular model for the unit cell of P4mm space group for BT in terms of atomic sizes. It is clear that Ba atom forms octahedral with oxygen atoms (BaO6) and Ti atom forms cuboctahedral with oxygen atoms (TiO12).
3.2 Morphological studies
The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can be used to study the microstructure nature of the perovskite materials. We have recorded SEM micrographs of Nd0.4Sr0.6MnO3 manganite samples calcined at 800–1200°C synthesized by auto-combustion method using FEI, Nova Nano SEM for the Nd0.4Sr0.6MnO3 perovskite and they are shown in Figure 7.
The average values of the particle size were analyzed by ImageJ software and they are found to be 50–425 nm for the Nd0.4Sr0.6MnO3 perovskites calcined at 800–1200°C, respectively. This clearly shows that the average particle size improves on increasing the calcination temperature. It confirms that the sample calcined at 800°C produces nano-material whereas that of at 1200°C gives bulk material.
3.3 Optical studies
Figure 8 shows photoluminescence (PL) excitation and emission spectra calcined at 800–1200°C. Figure 8a shows the excitation spectra of the Nd0.4Sr0.6MnO3 manganite in both the cases and contains an intense peak at 355 nm . It was monitored at an emission wavelength of 646 nm. The intensity of bulk material is two times larger than the nanomaterial. When both the materials were excited with 355 nm they give strong red color at 646 nm as shown in Figure 8b. It also contains weak peaks at 483–582 nm. The emission intensity obtained in the case of bulk material is further two times larger than the nanomaterial. This is due to the increase in crystallinity and particles size of the materials. Thus, the calcination affects the morphology and optical properties of perovskites even though the perovskite material was synthesized by auto-combustion method.
4. Applications of perovskite materials
The perovskite materials are extensively studied by researchers due to their attractive properties. The perovskite materials have wide applications in various fields, which are listed below:
Photo catalytic activity; e.g., LaFeO3 .
Photovoltaic solar cells; e.g., LaVO3 .
Phosphor materials in photoluminescence; e.g., Ho3+/Yb3+/Mg2+ doped CaZrO3 .
Solid oxide fuel cells; e.g., Gd0.7Ca0.3Co1−yMnyO3 .
Sensors and actuators; e.g., PbZrxTi1−xO3 .
Magnetic memory devices; e.g., Pt/La2Co0.8Mn1.2O6/Nb:SrTiO3 .
Magnetic field sensors; e.g., La0.67Sr0.33MnO3 and La0.67Ba0.33MnO3 .
Electric field effect devices; e.g., heterostructure of Pb(Zr0.2Ti0.8)O3/La0.8Ca0.2MnO3 .
Ferroelectric and piezoelectric devices; e.g., BaTiO3, PbTiO3 .
Semiconducting electronic devices; e.g., La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 .
High dielectric constant; e.g., Bi1−xSrxMnO3 (x = 0.4, 0.5) .
High temperature superconductor; e.g., BaPb1−xBixO3 .
Hypothermia; e.g., La0.7Sr0.3MnO3 .
Supercapacitor; e.g., KNi0.8Co0.2F3 .
The lanthanide based perovskite phosphors are one of them and have unique photoluminescence properties. The lanthanide ions are known for their narrow and sharp band emissions. They give emissions in the entire range of visible spectrum along with ultraviolet (UV) and near infrared (NIR) regions. These emissions are observed due to presence of meta-stable energy levels in the lanthanide ions. These levels have long lifetime and are responsible for very strong emissions. The lanthanide ions possess upconversion, downconversion and quantum cutting phenomena. In upconversion, the two or more than two low energy photons are converted into high energy photons. When a high energy photon is converted into low energy photons it is termed as downconversion process. However, in quantum cutting, a high energy photon is converted into two low energy NIR photons. These processes lead numerous technological applications in different fields, such as temperature sensing, solar cell, photonics, biological studies, light emitting diodes (LEDs), tunable phosphors, drug kinetics, red phosphors, etc. [64, 76, 77, 78, 79, 80, 81, 82, 83]. Figure 9 shows a block diagram for the lanthanide based perovskite phosphors, which shows the applications of these phosphors in different fields.
This chapter summarizes the basics of the perovskite structure, its stability and distortion. We have discussed the novelty of the perovskite materials, which accommodate different cations at A- and/or B-sites individually and/or simultaneously. We have also discussed various routes such as solid, liquid and gas phase synthesis for the preparation of perovskite materials mostly in the oxide powder forms. We also briefly described the phase identification of the perovskites and their structural analysis using Rietveld refinement of the XRD data by taking an example of BaTiO3 tetragonal perovskite. The morphological and optical studies were also incorporated. We have briefly listed various applications of perovskite materials including lanthanide based phosphor perovskites in different fields.
Conflict of interest
The authors declare no conflict of interest in the chapter.