**Abstract**

An attractive class of transition metal oxides (TMOs) have been freshly concerned with increasing research interest worldwide concerning stoichiometric and non-stoichiometric configurations as well, that usually exhibits a spinel structure. These TMOs will contribute substantial roles in the production of eco-friendly and low-cost energy conversion (storage) devices owing to their outstanding electrochemical properties. The current chapter involves the summary of the latest research and fundamental advances in the effectual synthesis and rational design of TMOs nanostructures with meticulous size, composition, shape, and micro as well as nanostructures. Also applications of TMOs such as effective photocatalyst, gas sensing, biomedical, and as an electrode material that can be utilized for lithium-ion batteries, and photovoltaic applications. Additionally, certain future tendencies and visions for the development of next-generation advanced TMOs for electrochemical energy storage methods are also displayed.

**Keywords:** transition−metal oxides nanostructures, oxides structures, lithium-ion batteries, gas−sensing, photovoltaics

#### **1. Introduction**

One of the motivating classes of material comprises transition metal oxides (TMO) that display an assortment of properties and structure as well (0–3). The nature of bonding present among metal and oxygen can be fluctuating from partially ionic to extremely covalent (or metallic). Owing to possess outer d-electron nature the properties of TMO are unusual. The remarkable wonder of TMO is its phenomenal array of electronic as well as magnetic properties. Therefore, oxides exhibiting metallic behavior such as RuO2, LaNiO3, and ReO3 are found at one class while oxides displaying extremely insulating properties including BaTiO3 are recognized as the other one [1, 2]. TMOs can be documented as the class of oxides that comprises of cation which has incompletely or partially filled d shell. This nature is due to their marvelous feature as they are motivating and scientifically supreme category of versatile solids. This class contains a wide-range of color, magnetic, and electric properties along with most researched classes to progress their

understanding of nature. As mentioned, their bonding fluctuates from partially ionic as in case of NiO and CoO to highly covalent such as OsO4, and RuO4.

Furthermore, metallic bonding also arises such as TiO, ReO3, and NbO. The crystal structure of TMOs varies from cubic symmetry to triclinic [3–5]. Further, binary oxides with the composition pattern of MO are commonly found to attain rock salt structure; but MO2 type composition involves rutile, fluorite, distorted rutile (complex structure). Possibly, significant features of TMOs are their aptitude to bear huge withdrawal from stoichiometry that is result of cations with variable valency. As an example, a portion of cuprous ion in copper (I) oxide (Cu2O) can be oxidized to cupric form that resulted in Cu2-xO which is a metal deficient composition. Similarly, ferric ion in iron (III) oxide (Fe2O3) can be reduced to resulted ferrous form, resulted in Fe2 + xO3 which are metal-rich composition [6–8]. Withdraw from stoichiometry in the case of non-TMOs that includes MgO is usually appeared as small and in the order of 10−4% even at an extreme temperature usually greater than 1700 °C. Other than this, TiO2 can put up roughly 1% of oxygen vacancies as well as titanium interstitials. There are exemptions to precede this generalization, as an example, ZnO which does not correspond to the tree of TMOs can provide a departure from the stoichiometric composition that varies from the range 10−2 to 10−1 at the temperature of 1000 °C [9–11].

This exhibition from ZnO is due to its wurtzite crystal structure that involves unoccupied interstices in the lattice of oxygen which is accomplished of acquiescent interstitial zinc. This phenomenon exhibits the importance of variable valency and crystal structure for the determination of specific oxide to bear substantial nonstoichiometry. This involves the zone of defect chemistry that solid-state chemist has focused devotion to the TMOs, in certain with the impartial of classifying the kinds of defect that are existing and their equilibrium concentrations as well. At the low concentrations conditions such as ~10−4% and point defects that comprise vacant sites (interstitial ions or atoms) are effectively treated via statistical thermodynamics [8, 11]. Furthermore, at the higher concentrations conditions such as ~10−2%; where certain association arises, the same method can be allowed to legal. This is due to the ionic defects that origins disturbances to the crystal's electronic structure. Moreover, an influential instrument in the study of defect chemistry contains the measurement of variations in semi-conductivity that is subsequent from fluctuations in defect concentration. These variations are followed as a function of temperature, and equilibrium oxygen partial pressure [8, 12].

Statistical thermodynamic handling of the defect equilibrium is typically unsuitable at the range of high defect concentrations that turn into the development of an identifiable superlattice. Owing to these conditions, the area of oxide covering the superlattice can be viewed as a different segment and the whole non-stoichiometry of oxide can be viewed as ascending from the mixture of such segments (two or more), instead of the arbitrary circulation of defects through single segment [8, 9]. These sorts of super-lattice assembling are thought to occur in high-temperature segment CeO2-x; this involves the dissociation upon chilling into a two-phase mixture that comprises CeO2 and Ce32O58. Meanwhile, in 1950, the idea about the crystallographic shear has been familiarized as well as recognized to designate the great withdrawals from stoichiometry detected in certain TMOs. Magnéli pronounced the nature of non-stoichiometry in the MoO3 employing these shear structures [12–14].

#### **2. Structure determination techniques**

The bulk MO structures have been regulated with broad and extremely precise XRD crystallographic plane studies [15]. Unluckily, inorganic structural chemistry

**5**

**2.1 V5+ oxides**

orthovanadate ( <sup>3</sup> *VO*<sup>4</sup>

chain which is metavanadate (VO3 )

*Rational Design and Advance Applications of Transition Metal Oxides*

related to MO dehydrated surface around oxide sustenance cannot be evaluated with XRD owing to the nonexistence of extensive range order which is greater than 4 nm in the surface MO over the layers. Native structures of MO dehydrated surface possibly bring into being via *in situ* molecular approaches of MO dehydrated supported with respect to spectroscopic analysis: Raman [16], UV–vis, infrared, chemi-luminescence, NMR established with solid-state assembly and XANES or

approachs offer structural particulars about numeral of O atoms coordinated to a cation for example MO4, MO5, MO6, and finally, M–O–M like symmetry that represent the incidence of adjacent neighbors. These kind of bridging among M–O–M bonds linkage are effortlessly obvious with Raman analysis; furthermore, this is likewise infrequently obvious for the overtone section of IR. Coupled Raman, the IR fingerprints, as well as isotopic oxygen exchange readings, are capable to begin the numeral of M = O which is pronounced as terminal bonds as an example for monooxo its linkage is M = O, dioxo bridging is related to O = M = O and finally tri-oxo M(=O)3 [17]. The isolated mono-oxo structures consist M = O symmetric stretch *v*s and it seems at a similar frequency for both approaches including Raman and IR analysis. Additionally, overtone section of IR reveals simply one band around 2*v*s. Subsequently, isolated di-oxo structures consist of the O = M = O functionality owns both stretching modes firstly, *v*s termed as symmetric and secondly, *v*as pronounced as asymmetric mode that can be disconnected through 10 cm−1. IR overtone region displays three bands around ∼2*v*s, *v*s + *v*as, and ∼2*v*as with extent upto ∼20 cm − 1 assortments. For isolated tri-oxo functionalities, more complex vibrational spectra appear and several bands will usually present in overtone, and stretching regions. Raman is normally quite sensitive to *v*s whereas IR is sensitive to *v*as. The moment

be perceived and the vibrations will degenerate [18]. Isotopic 16O or 18O exchange readings are capable to divide such kinds of degenerate vibrations through isotopic scrambling for oxygen. Mono-oxo structures correspond to two kinds of bands that are associated with symmetrical stretching mode and it will be existing owing to the vibration of M = 16O, and M = 18O as well. For di-oxo structures, three kinds of bands (symmetric stretching) will perform owing to firstly, 16O = M = 16O secondly, 18O = M = 18O, and thirdly, 16O = M = 18O vibrations. Besides, these fourth bands (symmetric stretching) should seem for tri-oxo functionalities which contains the

Additionally, isotopic swings owing to the replacement of the heavier 18O with the 16O isotope can correspondingly evaluated for oscillators based upon diatomic materials and it also matched with the detected isotopic shifts. Therefore, grouping of such sorts of measurements taken from the analysis of molecular spectroscopy which is combined with isotopic O atom exchange readings stay mandatory to achieve structures that are absolutely linked with MO dehydrated surface [3, 15, 19].

Inorganic chemistry of bulk vanadium with respect to its structural analysis that possesses the oxidation state of +5 is the greatest diverse between bulk MO. Additionally, this analysis has been evaluated from the broad-ranging examination of XRD. Further, Bulk vanadate (VO6) ions comprise of firstly, isolated

<sup>−</sup> ) secondly, dimeric pyrovanadate (V2 <sup>4</sup> O7

date ions are distinguished through amount of linking bonds with an assembly of V–O–V are existing firstly, orthovanadate (0) secondly, pyrovanadate (1), and finally metavanadate (2) structures. The charge in their structures is balanced via

*n n* H, etc. These characterizations

, then splitting of bands will not

2O, and lastly M18O3*)*.

<sup>−</sup> ), or polymeric

<sup>−</sup> structures. These four-coordinated vana-

*DOI: http://dx.doi.org/10.5772/intechopen.96568*

EXAFS, for certain nuclei including 51V, 95Mo, 1

when O = M = O bonds are detached through 90°

vibrations of firstly M16O3, secondly, M18O16O2, thirdly, M18O16

*Transition Metal Compounds - Synthesis, Properties, and Application*

10−1 at the temperature of 1000 °C [9–11].

temperature, and equilibrium oxygen partial pressure [8, 12].

**2. Structure determination techniques**

understanding of nature. As mentioned, their bonding fluctuates from partially ionic as in case of NiO and CoO to highly covalent such as OsO4, and RuO4.

Furthermore, metallic bonding also arises such as TiO, ReO3, and NbO. The crystal structure of TMOs varies from cubic symmetry to triclinic [3–5]. Further, binary oxides with the composition pattern of MO are commonly found to attain rock salt structure; but MO2 type composition involves rutile, fluorite, distorted rutile (complex structure). Possibly, significant features of TMOs are their aptitude to bear huge withdrawal from stoichiometry that is result of cations with variable valency. As an example, a portion of cuprous ion in copper (I) oxide (Cu2O) can be oxidized to cupric form that resulted in Cu2-xO which is a metal deficient composition. Similarly, ferric ion in iron (III) oxide (Fe2O3) can be reduced to resulted ferrous form, resulted in Fe2 + xO3 which are metal-rich composition [6–8]. Withdraw from stoichiometry in the case of non-TMOs that includes MgO is usually appeared as small and in the order of 10−4% even at an extreme temperature usually greater than 1700 °C. Other than this, TiO2 can put up roughly 1% of oxygen vacancies as well as titanium interstitials. There are exemptions to precede this generalization, as an example, ZnO which does not correspond to the tree of TMOs can provide a departure from the stoichiometric composition that varies from the range 10−2 to

This exhibition from ZnO is due to its wurtzite crystal structure that involves unoccupied interstices in the lattice of oxygen which is accomplished of acquiescent interstitial zinc. This phenomenon exhibits the importance of variable valency and crystal structure for the determination of specific oxide to bear substantial nonstoichiometry. This involves the zone of defect chemistry that solid-state chemist has focused devotion to the TMOs, in certain with the impartial of classifying the kinds of defect that are existing and their equilibrium concentrations as well. At the low concentrations conditions such as ~10−4% and point defects that comprise vacant sites (interstitial ions or atoms) are effectively treated via statistical thermodynamics [8, 11]. Furthermore, at the higher concentrations conditions such as ~10−2%; where certain association arises, the same method can be allowed to legal. This is due to the ionic defects that origins disturbances to the crystal's electronic structure. Moreover, an influential instrument in the study of defect chemistry contains the measurement of variations in semi-conductivity that is subsequent from fluctuations in defect concentration. These variations are followed as a function of

Statistical thermodynamic handling of the defect equilibrium is typically unsuitable at the range of high defect concentrations that turn into the development of an identifiable superlattice. Owing to these conditions, the area of oxide covering the superlattice can be viewed as a different segment and the whole non-stoichiometry of oxide can be viewed as ascending from the mixture of such segments (two or more), instead of the arbitrary circulation of defects through single segment [8, 9]. These sorts of super-lattice assembling are thought to occur in high-temperature segment CeO2-x; this involves the dissociation upon chilling into a two-phase mixture that comprises CeO2 and Ce32O58. Meanwhile, in 1950, the idea about the crystallographic shear has been familiarized as well as recognized to designate the great withdrawals from stoichiometry detected in certain TMOs. Magnéli pronounced the nature of non-stoichiometry in the MoO3 employing these shear structures [12–14].

The bulk MO structures have been regulated with broad and extremely precise XRD crystallographic plane studies [15]. Unluckily, inorganic structural chemistry

**4**

related to MO dehydrated surface around oxide sustenance cannot be evaluated with XRD owing to the nonexistence of extensive range order which is greater than 4 nm in the surface MO over the layers. Native structures of MO dehydrated surface possibly bring into being via *in situ* molecular approaches of MO dehydrated supported with respect to spectroscopic analysis: Raman [16], UV–vis, infrared, chemi-luminescence, NMR established with solid-state assembly and XANES or EXAFS, for certain nuclei including 51V, 95Mo, 1 H, etc. These characterizations approachs offer structural particulars about numeral of O atoms coordinated to a cation for example MO4, MO5, MO6, and finally, M–O–M like symmetry that represent the incidence of adjacent neighbors. These kind of bridging among M–O–M bonds linkage are effortlessly obvious with Raman analysis; furthermore, this is likewise infrequently obvious for the overtone section of IR. Coupled Raman, the IR fingerprints, as well as isotopic oxygen exchange readings, are capable to begin the numeral of M = O which is pronounced as terminal bonds as an example for monooxo its linkage is M = O, dioxo bridging is related to O = M = O and finally tri-oxo M(=O)3 [17]. The isolated mono-oxo structures consist M = O symmetric stretch *v*s and it seems at a similar frequency for both approaches including Raman and IR analysis. Additionally, overtone section of IR reveals simply one band around 2*v*s. Subsequently, isolated di-oxo structures consist of the O = M = O functionality owns both stretching modes firstly, *v*s termed as symmetric and secondly, *v*as pronounced as asymmetric mode that can be disconnected through 10 cm−1. IR overtone region displays three bands around ∼2*v*s, *v*s + *v*as, and ∼2*v*as with extent upto ∼20 cm − 1 assortments. For isolated tri-oxo functionalities, more complex vibrational spectra appear and several bands will usually present in overtone, and stretching regions. Raman is normally quite sensitive to *v*s whereas IR is sensitive to *v*as. The moment when O = M = O bonds are detached through 90° , then splitting of bands will not be perceived and the vibrations will degenerate [18]. Isotopic 16O or 18O exchange readings are capable to divide such kinds of degenerate vibrations through isotopic scrambling for oxygen. Mono-oxo structures correspond to two kinds of bands that are associated with symmetrical stretching mode and it will be existing owing to the vibration of M = 16O, and M = 18O as well. For di-oxo structures, three kinds of bands (symmetric stretching) will perform owing to firstly, 16O = M = 16O secondly, 18O = M = 18O, and thirdly, 16O = M = 18O vibrations. Besides, these fourth bands (symmetric stretching) should seem for tri-oxo functionalities which contains the vibrations of firstly M16O3, secondly, M18O16O2, thirdly, M18O16 2O, and lastly M18O3*)*. Additionally, isotopic swings owing to the replacement of the heavier 18O with the 16O isotope can correspondingly evaluated for oscillators based upon diatomic materials and it also matched with the detected isotopic shifts. Therefore, grouping of such sorts of measurements taken from the analysis of molecular spectroscopy which is combined with isotopic O atom exchange readings stay mandatory to achieve structures that are absolutely linked with MO dehydrated surface [3, 15, 19].
