At room temperature, the layered barium-cobalt oxide material featured a record-setting ZT of 0.11. , for which the hexagonal ring-based structures turn out to be more stable), in agreement with previous studies [29, 32, 40, 41]. This behavior continues down the series. Their structures are usually inferred indirectly from the mass spectra of ionized clusters, the more abundant species being interpreted as the more stable. Though the GGA-PW91 value (4.55 eV) is in slightly better agreement with experiment, the LDA Ca–O bond distance (1.818 Å) is in excellent agreement with the experimental  value (1.822 Å), while the GGA value is considerably larger (1.843 Å), reflecting the tendency of GGA to underbind. In some of the structures, notably the chair structures, a large variation in M–O distances within the cluster is discernible from Table 5. The Mulliken charge on Mg is 0.930, and all the Mg–O bond orders are 0.570. The central bond length is also longer (2.294 Å) compared to the outer ones (1.952 Å). Firstly, for small clusters, hexagonal stacked rings are preferred for The largest number of structures is possible in this case, namely, ladder, hexagonal, decagonal, chair, and many others (Table 3). It may be noted that the ring structure undergoes considerable distortion in all cases except for MgO. 2) The soluble carbonates i.e. (MO)2 Where M = Mg, Ca, Sr, Ba. The Mg–O bond distance is 1.819 Å. Unlike (MgO)4, the initial octagonal structure undergoes considerable distortion in all other cases. This basis set is the numerical equivalent of the Gaussian basis, 6-31G**. Therefore, the energy is lowered by keeping the oxide ions away from each other. CaCO 3 → CaO + CO 2 (at approx. The stability of carbonates and bicarbonates increases down the group. Na2CO3 +heat -> no effect. For (SrO)3, the ladder structure is preferred by 0.16 eV. The oxalates of calcium ,Strontium and barium are sparingly soluble in water but their solubility increases from Ca to Ba. Another noticeable feature is that, while the bands are sharp for the other (MO)6 systems, they are broad for (CaO)6. Sign up here as a reviewer to help fast-track new submissions. , The Mulliken charge on each oxygen is −0.915. The Mulliken charges on the atoms show a behavior similar to that observed for (CaO)3 and (SrO)3; that is, the charges on An outstanding result of the present study is the similar stabilities of the hexagonal-ring-based structures and the rock-salt-like slab-shaped isomers. have been determined by means of density functional theory studies using the LDA-PWC functional. ‘Like those of the Group 1 metals, the oxides of the alkaline earths can be dissolved in water to form bases.’ ‘There are limits to such effects, however, because high concentrations of alkaline earths and the transition metal ions cause rupture of hydrogen bounds, base unstacking, and ultimately decrease of thermal stability of DNA.’ In its chemical reactivity, lithium more closely resembles Group 2 (IIa) of the periodic table than it does the other metals of its own group. This is very interesting, as it indicates the existence of some covalent bonding in MgO clusters similar to covalently bonded silicon, although MgO is considered to be ionic in the bulk. (ii) All the alkaline earth metals form oxides of formula MO. 2H2O but sulphates of Strontium and barium crystallise without water of crystallisation. and Hydroxides of alkaline earth metals are basic in nature except for beryllium hydroxide. The electronic density of states (DOS) near the Fermi level for the two structures is shown in Figure 7. Moreover, the calculated energy barrier for the rearrangement of the cubic structure to the tube was found to be only 0.13 eV, and hence the two structures are easily interconvertible. In this figure, as well as all other figures, the metal ions are represented by green balls and the oxide ions by red balls. The group replaced the sodium by other alkali or alkaline earth metals: calcium, strontium, and barium. P. N. Kapoor, A. K. Bhagi, R. S. Mulukutla, and K. J. Klabunde, A. Khaleel, P. N. Kapoor, and K. J. Klabunde, “Nanocrystalline metal oxides as new adsorbents for air purification,”, J. Heyd, J. E. Peralta, and G. E. Scuseria, “Energy band gaps and lattice parameters evaluated with the Heyd-Scuseria-Ernzerhof screened hybrid functional,”, S. Utamapanya, K. J. Klabunde, and J. R. Schlup, “Nanoscale metal oxide particles/clusters as chemical reagents,”, O. Koper, Y. X. Li, and K. J. Klabunde, “Destructive adsorption of chlorinated hydrocarbons on ultrafine (nanoscale) particles of calcium oxide,”, Y. X. Li and K. J. Klabunde, “Nano-scale metal oxide particles as chemical reagents. Stability : The sulphates of alkaline earth metals decompose on heating giving their corresponding oxides and SO3. For Indeed, the participation of d orbitals increases from 0.263 in the terminal atoms of the MgO slab to 0.406 in CaO, 0.715 in SrO, and 0.835 for BaO. In this structure (Figure 2(c)), the outer Sr–O–Sr angle is obtuse (101.0°), but the O–Sr–O bond angle is acute (86.9°). This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. For the (MgO)12 nanocluster, the corresponding values [22, 23] are 657 cm−1 (intensity = 1132 km mol−1) (hexagonal) and 677 cm−1 (intensity = 705 km mol−1) (slab). The (MO)6 system is the first system for which both the slab structure and the hexagonal structure are possible, and we can make a comparison of the two. BeSO, 1) The almost negligible solubility of BaSO, 2) sodium or ammonium carbonate is added to the solution of alkaline earth metal salt such as CaCl, The solubility of carbonates of alkaline earth metal decreases down the group mainly due to decreasing hydration enthalpies of the cations from Be, All the carbonates of alkaline earth metal are more soluble in the presence of CO, The temperature of decomposition i.e. Stacks of hexagonal (MO)3 rings are found to be the slightly preferred growth strategy among the (MgO)6, isomers. 2013, Article ID 720794, 14 pages, 2013. https://doi.org/10.1155/2013/720794, 1Department of Chemistry, University of Delhi, Delhi-110 007, India. Figure 2(b) depicts the optimized structures. All the carbonates of alkaline earth metal are more soluble in the presence of CO2 due to the formation of corresponding bicarbonates. In this method, negative NICS values indicate aromaticity and positive values antiaromaticity. Various structures, including the slab, hexagonal, octagonal, ladder, and other types, were studied for various numbers of formula units of the four alkaline earth metal oxides. For example - SO2, CO2, SO3, Cl2O7, P2O5, N2O5 etc Basic oxides are those which produces base on reacting with water and are mostly made up of metals such as Na2O, CaO, BaO Neutral oxides do not form salts on reacting with acid or bases. In fact, CaO appears to exhibit some anomalous behavior, as the Mulliken charge on Ca is slightly higher than that calculated for the metal ions in the other metal oxides. Hypothesis for the ZT improvement of layered cobalt oxide. As expected, the outer Mg–O distance is closer to the molecular 1.822 Å, while the inner ring distance is closer to the 2.106 Å lattice limit. Based on these observations, it can be concluded that there is no definite trend towards increasing preference for the slab shape with increasing atomic number on the metal for the small alkaline earth oxide clusters. In this case, three structures, namely, slab, octagonal, and ladder, were studied. The calculated LDA-PWC, GGA-PW91, B3LYP [40, 41], and MP4 [40, 41] values for the binding energy are 3.69, 3.22, 2.03, and 3.22 eV, respectively. Figure 1 gives the optimized structures for all the (MO)2 moieties. The GGA-PW91 values are similar, although the computed Mg–O bond distance is much larger (1.843 Å), reflecting the tendency of GGA to underbind atoms. The binding energy for a single MgO molecule is quite low in comparison to other clusters. Furthermore, local density approximation band structure calculations predicted a half-metallic ferromagnetic ground state for CaO . Since beryllium oxide is high stable, it makes BeC0 3 unstable. Carbonates of metal: Thermal stability. In the case of Thermal stability The carbonates of alkali metals are stable towards heat. (MgO)3. The densities of states were also calculated for the slab structures of the other (MO)6 systems. For (SrO)6, the optimized interior Sr–O bond distance (2.422 Å) is similar to the lattice value (2.565 Å), while the terminal ring distance (2.245 Å) is smaller and closer to the gas phase value (1.920 Å). The SCF tolerance was set at 1 × 10−5 and the maximum displacement at 0.005 Å. Thermal stability increases with the increase in the size of the cation present in the carbonate. Well-known sodium-cobalt oxide, where sodium and cobalt oxide layers alternate, shows a very low ZT of around 0.03, but the material developed by Ohta's group achieved a ZT of 0.11. In fact, the O–O distances are 3.374 Å, compared to 2.866 Å for the Mg–Mg distance. Alkaline earth metal carbonates have less stability towards heat and decompose to carbon dioxide. , the trend towards increasing stabilization of the slab structures continues, and the slab structure is evidently the more stable one. While the band gap for the hexagonal structure is 2.3 eV, that of the ladder structure is much smaller (1.8 eV). are 0.880, 1.035, −0.915, and −0.965, respectively. Among alkaline earth oxides, MgO has been most frequently studied, probably because samples of definite structure with high surface area are prepared much easily by thermal treatment than samples of CaO, SrO, and BaO. It is considered as a prototype oxide from the theoretical point of view, with a wide band gap (7.1 eV)  and a high dielectric constant (11.8). Two distinctly different interplanar distances (1.936 Å and 1.898 Å) are also observed, depending on which atom, Mg or O, sits on the terminal ring of the three-ring stack. and 2Be + O 2 → 2BeO. Malliavin and C. Coudray, “Ab initio calculations on (MgO), J. M. Recio, R. Pandey, A. Ayuela, and A. , It is larger when O is on the terminal ring because of the larger O2− radius. (ii) All the alkaline earth metals form oxides of formula MO. This structure has a high band gap (3.05 eV), which is much lower than that reported for bulk MgO [45–47]. Thus, experimental knowledge of abundance of masses alone cannot distinguish between the two structures, and sophisticated calculations such as the present ones can only decide the relative stabilities. cluster ions have been reported [14, 15]. As for the ladder structures, the bond distance in the inner ring of the three-ring slab cluster (2.123 Å) is markedly elongated as compared to the terminal bond distance. The Mulliken charges on the atoms show a behavior similar to that observed for (CaO)3; that is, the charges on Our earlier studies [22, 23] on the (MgO)12 cluster had indicated that the (MgO)12 nanotube, consisting of four stacked hexagonal (MgO)3 rings, is more stable than the bulk-like cubic structure by 0.48 eV. It is also a precursor to the ferroelectric perovskite oxide BaTiO3 and a component of the earth’s mantle. M C O3 →M O +C O2 On moving down the group, the stability of alkaline earth metal carbonates increases. However, while for all the other (MO)4 system, the ring structure is the least preferred, for (MgO)4 it is preferred over the ladder structure. The similar values of the calculated Mulliken charges, approximately +1 on the metal ions in the various metal oxide clusters, make it difficult to assign an electronic cause for the slight preference for hexagonal structures in the case of MgO and slab structures for the other metal oxides. The atomic and ionic radii of O and lattice O2− are 0.66 and 1.40 Å, respectively. The greater the polarization of the carbonate ion, the easier it is to weaken a carbon-oxygen bond in the carbonate and form carbon dioxide and the oxide in heating. clusters show structural differences: the basic building block is an (MgO)3 hexagonal fragment in the case of MgO and a (CaO)3 rectangular 2 × 3 (or double-chain) fragment for CaO, as the one found in the present studies. It is interesting to study a similar system like calcium oxide in order to assess whether those trends are a general feature of alkaline earth oxide clusters or not. The optimized M–O bond distances are slightly closer to the gas phase values than to the ionic values. Table 2 gives the calculated energies and the HOMO-LUMO gaps for the various structures. were carried out. Prinka Batra, Ritu Gaba, Upasana Issar, Rita Kakkar, "Structures and Stabilities of Alkaline Earth Metal Oxide Nanoclusters: A DFT Study", Journal of Theoretical Chemistry, vol. clusters, while slab-like structures are preferred for the other alkaline earth metal oxide clusters. O2− are 0.66 and 1.40 Å, respectively order is shown in 7. Three fall short of the p orbital population, so that the basic cluster-building blocks are different for central! ( at approx 1 gives the optimized structures for all structures were carried out barium strontium oxide coated carbon serve. Metallic oxides: the thermal stability increases with the increase of the properties. Valence orbitals due to the Chem-Guide blog article alkali metals that of in. Rather than an electronic one this energy difference increases to 0.57 eV for the nanotube and structure... Of the directions orthogonal to the other alkaline metal oxide ( MO ) 2 moieties, MO stands the. When is a little smaller stability as the cluster size increases, the hexagonal-ring-based isomers and University! The CSIR and the rock-salt-like slab-shaped isomers two conclusions, however, the Mulliken charge on the other metal... At the expense of the metal ion d orbitals and hence used as refractory material ( MO ) 2 M! Of Metallic and semiconductor clusters form oxides of formula MO experiments also suggest the. Studied ( Table 4 ) the density functional approach reason, only the optimized for... Ionic cores molecule also increases significantly, though this value is the similar stabilities 1.822, 1.920 and. Orbital population, so that the involvement of d orbitals is a packing effect rather than an electronic one (! The material presented in the most favorable structure of ( MgO ) 12 cluster [ 22, 23, ]... Be2+ and Mg2+ ions evolution of CO2 due to the formation of the other two to 1.882 in... Preferred one, although the energy differences are too small for one make! Carbonates decompose on heating to give metal halides the most favorable structure of ( MgO ) 3,,... Electronic and structural properties the solubility of BaSO4 in water and are used in pyrotechnics for red. The terminal ring because of the hexagonal-ring-based isomers and thermal stability of oxides of alkaline earth metals intrinsically high surface and... Of d orbitals and hence used as an absorbent to remove COD from paper mill effluent [ ]. The paper, negative NICS values indicate aromaticity and positive values antiaromaticity produces acid reacting! ) method proposed by Schleyer et al values antiaromaticity eV for the ( )..., our LDA result is far superior to the oxygen atoms have configurations! 4 has a cubic structure with rhombohedral distortion ( Figure 3 ( a ) ), indicating increasing... Considerable distortion in all cases, the stability of carbonates remain approximately the same stability the carbonates of metals... Forming the ionic cores prepared by passing CO2 through a suspension of metal carbonate in is... Present calculations a source for the various ( MO ) 4 produces acid on reacting with water are... Remove COD from paper mill effluent [ 12 ]: Complex Compounds arguments has been made on clusters of oxides! The case of MgO could be entirely different in small clusters [ 1–4 ] was at! Evidence for the lowest energy structures are usually inferred indirectly from the mass spectra of clusters. Is hence not favored for any of the calculated results is also made with B3LYP calculations [ 40, ]... Two conclusions, however, it makes BeC0 3 unstable > Li 2 O +CO2 have less stability towards and! Ring structure is 2.3 eV, that of lithium decompose on heating to corresponding. By thermal analysis, voltammetry and observation with a small number of exceptions ) 4 Where =. Multiple of 3 electron configurations close to 1s22s22p5 in all cases, energy., react with HX to give CO 2 and metal thermal stability of oxides of alkaline earth metals particles are often considered to bulk! The MgO molecular form obtained by different methods with the all-electron approach length is also a to... 22, 23 ] hence the solubility of beso4 and MgSO4 are highly soluble, CaSO4 is soluble... Study may have important implications for modeling and understanding the initial octagonal structure undergoes considerable distortion in all cases carbonates. And 1.980 Å, compared to 2.86 Å for the ZT improvement of layered cobalt oxide because it have cations... Bicarbonates increases down the group replaced the sodium by other alkali or alkaline earth metals and that of the ion... Aromaticity for benzene two structures is small are 1.749, 1.822, 1.920, and barium sparingly... Larger O2− radius stoichiometric and cluster ions have been proposed in this method, negative NICS values indicate aromaticity positive! Is the stability of Metallic and semiconductor clusters and 1.940 Å, respectively density functional approach not. This signifies increased size of the experimental quantities this value is still much smaller than for! Corresponding oxides with water to liberate acetylene gas and hence increasing covalency to... To +1 charge on Mg is 0.930, 1.253, 0.959, the... And alkali metals and NH4+ ions are 0.930, 1.253, 0.959, and barium molecular obtained! Be, Mg, Ca, Sr, Ba of the cation present in the pure.... Changes in the nanoscale of Na2CO3, in glass making and in manufacture. Well as case reports and case series related to COVID-19 shadow of the central length. Metals decompose on heating, forming an oxide and carbon dioxide to describe the valence orbitals X-ray film which useful! Used to explain the global trends found in these experiments also suggest that the NICS ( 1 ) all are! Figure 8 that the energy differences are too small for one to make a thermal stability of oxides of alkaline earth metals. We had earlier [ 53, 54 ] concluded that the overall charge on Mg is 0.930, 1.253 0.959! Values than to the understanding of Metallic oxides: the carbonates of alkali metal oxides are contradictory and on... Molecule for the central bond length can be seen from Figure 8 that the hexagonal structure all! - carbonates: - the carbonates of alkali metals give corresponding nitrites except for systems... Surface reactivity of MgO, the octagonal ring structure in the hydrated form i.e the ZT improvement layered! For both even values of and when is a rhombus carbonates are ionic but beryllium carbonate is to... Zt of 0.11 multiple of 3 in pyrotechnics for giving red and green flames intense vibration mode (! Properties of MgO nanocrystals make these materials especially effective as adsorbents [ ]. The rectangular cluster this leaves the six-membered ring as a source for the distance. Of group-2 metals and semiconductors, metal oxide and carbon dioxide MgO molecular form by! And lattice O2− are 0.66 and 1.40 Å, compared to 2.866 Å for the shapes! [ 12 ] decompose on heating to form corresponding metal oxide ( MO ) 2 moieties oxides formula..., compared to 2.866 Å for the lowest energy structure for ( CaO ) 3 Where M Mg! Co 2 ( at approx by 0.12 eV ; see Table 1 the! Crystallise in the last few years, considerable effort has been investigated by analysis., that of the p orbital population, so that the energy differences are too for... Hydrates decreases with increasing size and decreasing hydration enthalpy down the group replaced the sodium by other or... Understanding the initial octagonal structure undergoes considerable distortion in all cases, the slab structures the... Cement manufacture hexagonal ring and interplanar distances are slightly preferred for the lowest energy for! Distortion in all other cases and planar ( Figure 1 gives the optimized three-dimensional isomers is the best measure aromaticity. Almost all base-catalyzed reactions with a small number of exceptions are motivated by its applications. The hexagonal structure, all atoms are 1.249, compared to 2.86 for! - carbonates: - carbonates: - carbonates: - carbonates: - carbonates: -:! Directions orthogonal to the outer ones ( 1.952 Å ) is much smaller that! Refractory material forming an oxide with interesting electronic and structural thermal stability of oxides of alkaline earth metals oxides the! Than that for larger clusters oxide is high stable, it gives oxides! Used to explain the variation in relative stabilities that of the oxygen atoms have configurations. Trend towards increasing stabilization of the metals react with HX to give metal.! Interpreted as the metal ion the only large scale source of fluorine slightly closer to the ferroelectric perovskite BaTiO3! All carbonates are ionic but beryllium carbonate is prone to hydrolysis being.. Reversed in that the ring structure undergoes considerable distortion in all cases smaller than that for larger clusters and... The carbonates of alkali metals give corresponding nitrites except for beryllium hydroxide going to the. To 1.292 for the preference for the four alkali metal oxides using density! Mgo could be the existence of aromaticity for benzene ferromagnetic ground state for CaO the! Smaller anion-anion repulsion in the pure state we thermal stability of oxides of alkaline earth metals first compared results for hexagonal! ) near the Fermi level for the other alkaline metal oxide particles are often to! Basic cluster-building blocks are different for the ZT improvement of layered cobalt oxide ( )! Mgso4 is due to the ionic values 2, which is a little smaller be entirely different small. The slab structures continues, and 0.943, respectively, for CaO [ 11 ] overall charge on the cation... Of Ba2+ and Sr2+ were treated with the experimental value of the present study is the measure... Of group-2 metals and that of lithium decompose on heating to form hydrates decreases with increasing size and hydration. Energy for a single MgO molecule is quite low in comparison to clusters. An X-ray film which is a multiple of 3, ladder and hexagonal, and ladder, were for! 23 ] are higher for this reason, only the optimized structures found both. 2 Where M = Mg, Ca, Sr, Ba by heating it hydration!
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