**Abstract**

There is a constant need for newer exceptional materials with better than ever properties to achieve new prerequisites of the future society and progress inventive industrial improvement. The potential to combine these oxides in composite structures to produce multifunctional materials has rekindled interest in perovskites (ABO3) compounds over the past 10 years. Because of its intriguing characteristics, such as ferroelectricity, piezoelectricity, superconductivity, multiferroicity, photocatalysis, enormous magnetoresistance, dielectric, ionic conduction characteristics, etc., a huge variety of perovskite types have been thoroughly explored. Current applications for perovskite solids include electronics, geophysics, astronomy, nuclear, optics, medicine, the environment, etc. Perovskite compounds have distinctive features that make them suitable for a variety of commercial and technological applications, including capacitors, nonvolatile memories, photo-electrochemical cells, catalysts in contemporary chemistry, actuators and sensors, ultrasonic and underwater devices, drug delivery, spintronics devices, tunable microwave devices, and many others. Potential applications for nanoscale perovskites include energy storage, fuel cells, nanomedicine, molecular computing, nanophotonics adjustable resonant devices, catalysts, and sensors. Nanoscale perovskites have intriguing features that are comparable to or better than those of bulk perovskites. This review includes topics such as perovskite structured materials' chronology, classification, production, crystal structure, special physical properties, and applications.

**Keywords:** perovskite, ceramics, ferroelectricity, multiferroics, ABO3

### **1. Introduction**

Perovskites were called for the Russian aristocrat and mineralogist Count Lev Aleksevich Von Perovski (1792–1856), who first discovered the calcium titanium oxide (CaTiO3) structure in the Ural Mountains of Russia in 1839 [1]. The perovskites materials often contain the generic formula ABX3, where X is an anion that bonds to both A and B, two cations of quite different sizes [2]. Although X is frequently oxygen, it is also feasible for it to be other big ions such halides, sulphides, or nitrides. Many oxide compounds from a few homologous perovskite series are known, including A*<sup>n</sup>* + 1B*n*O3*<sup>n</sup>* + 1 Ruddlesden-Popper, A*n*B*n*O3*<sup>n</sup>* + 1 Dion-Jacobson, Bi2A*n*-1B*n*O3*<sup>n</sup>* + 3

Aurivillius series and some others [3–5]. The perovskite structures are exists in different form such as: ABO3-perovskite (ex: BaTiO3, CaTiO3), A2BO4-Layered perovskite (ex: Sr2RuO4, K2NiF4), A2BB<sup>0</sup> O6-Double perovskite (ex: Ba2TiRuO6) and A2A<sup>0</sup> B2B<sup>0</sup> O9-Triple perovskite (ex: La2SrCo2FeO9), etc. [6–8]. Because of its intriguing range of features, including as superconductivity, insulator-metal transition, ionic conduction characteristics, dielectric properties, and ferroelectricity, perovskite type oxides have been researched extensively [9–12]. One of the most typical solid-state physics structures, perovskite, contains a considerable variety of anions in addition to the majority of the metal ions from the periodic table. Numerous theoretical and experimental studies have focused on perovskite materials, typically ABO3, over the past few years. These solids are currently assuming a significant role in fields such as electrical ceramics, refractories, geophysics, material science, astrophysics, particle accelerators, fission-fusion reactors, heterogeneous catalysis, environment, etc. [13–22]. In order to maintain their original crystalline structure, perovskite structured oxides can take significant substitutions in either one or both of their cationic sites (i.e., the A and B sites). Through the partial replacement of the cationic site(s) with foreign metal ions, this property enables the chemical customization of the materials, changing their structural, microstructural, electrical, and magnetic properties [23–25]. Perovskite-like compounds and the oxides of the perovskite type have many uses in physics and chemistry. These materials' physicochemical characteristics are influenced by their pore structure, surface morphology, particle size, exposed lattice plane, lattice defect, and surface morphology [26–29]. Many perovskite-type oxides and perovskite-like oxides have been created and studied so far in order to better understand their physicochemical characteristics. The ideal perovskite is referred to as the cubic perovskite. Due to their straightforward crystal structures and distinctive ferroelectric and dielectric characteristics, this class of materials holds enormous potential for a range of device applications. Perovskites solids, one of the most prevalent and frequently studied minerals, are extensively researched as potential substrate materials [30, 31]. Due to its unique ferroelectric, thermoelectric, pyroelectric, dielectric, and optoelectronic properties, perovskite-structured ceramics (ABO3, where A and B are two cations) have recently gained popularity on a global scale [32–36]. Perovskite ceramics are used in a variety of exceptional applications, including wireless technology, sensors, actuators, screens, capacitors, random access storage, and adjustable microwave devices [37–44].

### **2. Perovskite structure**

It is known that a perovskite type ABO3 oxide structure may maintain the stability of almost 90% of the metallic natural elements listed on the periodic table. The crystal perovskite calcium titanate is where the atomic arrangements in this structure were originally discovered (CaTiO3). The naturally occurring CaTiO3 species are depicted in **Figure 1** (accompanied by Lev Aleksevich von Perovski). The majority of ABO3 type oxides crystallize in the CaTiO3 mineral's (relatively) straight forward form or in a structure quite similar to it. Even though CaTiO3 was later discovered by Megaw in the United Kingdom, this straightforward cubic form has remained the name perovskite [45]. Subsequently, it was quickly verified with Miyake and Ueda's work [46]. Perovskites show brittle toughness, a sub-metallic to metallic sheen, colorless streaks, a cube-like structure, and imprecise cleavage. Brown, gray, black, orange, and yellow are among the colors.

*Perovskite Structured Materials: Synthesis, Structure, Physical Properties… DOI: http://dx.doi.org/10.5772/intechopen.106252*

#### **Figure 1.**

*Lev Aleksevich von Perovski and the perovskite mineral species (CaTiO3).*

**Figure 2.** *Typical perovskite material crystal structure.*

The structural formula for perovskite is ABO3, where A and B are cations of varying sizes and O is the anion. Smaller than the B cation is the cation at the A location. According to **Figure 2**, the A atom has a 12 fold co-ordination number while the B atom has a 6 fold co-ordination number.

Divalent A cations typically reside in the corners of a cube at corner location and are 12 fold coordinated by oxygen anions (0, 0, 0). Tetravalent B cations are located in the body's core (½, ½, ½) and are found inside that oxygen octahedron. The position (½, ½, 0) of the oxygen atoms in the cubic lattice's face centre. The structure is typically represented as a three-dimensional network of BO6 octahedra with regular

corner links. The A atom's coordination number is 12. A perfect perovskite has a network of shared corner BO6 octahedra with all B-O-B angles at 180 degrees, according to its structure. The proportion of A to B ionic size and the electronic arrangement of the metal ions are two indicators of the structural distortion in perovskite. Perovskite typically exhibits two different structural distortions, one of which is the tilting of the BO6 octahedral and the other of which is the off-centering of the B ion in the BO6 octahedral. The first kind relates to a phase transition that is displacive, and the second type refers to a phase transition that is order-disorder [47, 48]. Tolerance factor (t0 ), introduced by Goldschmidt, can be used to evaluate the prediction criteria for identifying the formability of perovskite structure [49].

$$t' = \frac{(r\_A + r\_O)}{\sqrt{2} \cdot (r\_B + r\_O)}\tag{1}$$

where rA and rB are the ionic radii of the A and B cations, respectively, and rO is the oxygen anion's ionic radius (in units). When t<sup>0</sup> is less than one, the BO6 octahedron tilts; nevertheless, when t<sup>0</sup> is more than one, the smaller B cation centres off. Off-centering is mostly caused by larger A and smaller B ions, which causes BO6 octahedron to compress. The BO6 octahedron creates a cavity where the B ion tilts more effectively [50]. It has been discovered throughout time that whereas few perovskite-type oxides exhibit the straightforward cubic structure at ambient temperature, many do so at higher temperatures. The ideal perovskite-type structure has a cubic space group Pm3m-Oh [51].

### **3. Classification of perovskites**

Numerous perovskite-based combinations with a variety of physical properties result from the flexibility of the ABO3 perovskite crystalline structure and its capacity to accommodate a broad range of cations with various oxidation states as well as cation or anion vacancies. The two main categories of oxide phases are the ternary ABO3 kind and their solid solutions, and the more modern complicated type compounds (AB<sup>0</sup> xB″y)O3, where B<sup>0</sup> and B″ are two distinct elements in various oxidation states and x + y = 1. On the basis of oxidation states, the ternary oxides can be divided into oxygen and cation deficient species and A1+B5+O3, A2+B4+O3, A3+B3+O3 [52, 53]. The flowchart below **Figure 3** displays the comprehensive classification.

A(Bx 0 By″)O3 is a complex perovskite type compound that can be separated into A (B<sup>0</sup> 0.67B″0.33)O3 compounds that contain twice as much a lower valence state element as a higher valence state element, those that have A(B<sup>0</sup> 0.33B″0.67)O3, which has twice as much of the higher valence state element as the lower valence state element. Those with A(B<sup>0</sup> 0.5B″0.5)O3, those with equal levels of the two B components A(Bx 0 By″)O3-*<sup>z</sup>* and oxygen-deficient phases. The A and B cations' electron orbitals are typically near to 2<sup>+</sup> and 4<sup>+</sup> , correspondingly, but in a few unique situations, they may be 3<sup>+</sup> and 3<sup>+</sup> if the B3+ cation has a six coordination. The oxygen anion array may be bent or displaced as a result of the valence variation at the A cation site, which will buckle the (AO3)4� layers. The octahedra with B cations at their centres may become distorted as a result of this buckleing. Due to their multiple valencies or unique 3d and 4d electron configurations, transition metal elements are good candidates to fill the B cation position because they have the adaptability needed to withstand this impact. This explains why transition metal oxides typically exhibit exceptional physical properties and feature perovskite-like structures. The oxygen and cation deficient phases will be viewed as

*Perovskite Structured Materials: Synthesis, Structure, Physical Properties… DOI: http://dx.doi.org/10.5772/intechopen.106252*

**Figure 3.** *Sorting out perovskite structures.*

having a significant amount of vacancies rather than being just out of stoichiometry. Many of them differ from the complex perovskite compounds, which contain various elements in various valence states, in that they contain B ions of one element in two valence states [54, 55].
