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Investigation of the rare earth-based LaYO3 (Y = Cr and Mn) perovskites by ab-initio approach
Journal Pre-proofs Research paper Investigation of the rare earth-based LaYO3 (Y= Cr and Mn) perovskites by ab-initio approach N.A. Noor, Ujala Anwar, A. Mahmood PII: DOI: Reference:
S0009-2614(19)31012-7 https://doi.org/10.1016/j.cplett.2019.137031 CPLETT 137031
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Chemical Physics Letters
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28 September 2019 12 November 2019 7 December 2019
Please cite this article as: N.A. Noor, U. Anwar, A. Mahmood, Investigation of the rare earth-based LaYO3 (Y= Cr and Mn) perovskites by ab-initio approach, Chemical Physics Letters (2019), doi: https://doi.org/10.1016/ j.cplett.2019.137031
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Investigation of the rare earth-based LaYO3 (Y= Cr and Mn) perovskites by ab-initio approach N.A. Noora*, Ujala Anwarb, A. Mahmoodc a
Department of Physics, University of Lahore, Lahore 54000, Pakistan
b
Institute of Chemical Sciences, Bahauddin Zakariya University (BZU), Multan, Pakistan
c
College of Engineering Chemical Engineering Department King Saud University Riyadh, Saudi
Arabia * Corresponding author Email: [email protected] Abstract Here, we report the ab-initio studies to explore physical aspects of Lanthanide-based perovskites LaYO3 (Y= Cr and Mn), using full-potential linearized augmented plane waves logic. The calculated values of lattice constants were 3.91Å and 3.86Å for LaCrO3 and LaMnO3 respectively with PBEsol-GGA, comparable with available experimental data. Band structure and density of states played pivotal role in determination of the electronic properties. Figuring the exchange splitting energies (Δx(d) and Δx (pd)), crystal field energy (ΔCF) and Jahn-Teller energy (ΔJT) traverse the ferromagnetic semiconducting nature of studied La-perovskites. In addition, BoltzTraP code implemented to interrogate the thermoelectric properties. Key Words: Lanthanide-based perovskites, Density functional theory (DFT), ferromagnetic (FM) characteristic, Exchange splitting and Thermoelectric properties,
1. Introduction Perovskite oxide compounds have brought great attention by the researchers as they exhibit wide range of crystal structures [1] and easily tunable physio-chemical and catalytic properties via transition metal doping [2, 3]. Furthermore, the high thermo-chemical stability, electrochemical behavior and ionic conductivity of perovskite oxides make them auspicious for use in industry [4, 5]. Perovskite oxides betray ABO3 like crystal structure, where site A preserves rare-earth metals (e.g. La, Er, Sm, Dy etc.) or alkaline earth metals (e.g. Ca, Sr etc.) while B sites being occupied by transition metals (i.e. Sc, Ti, Cr, Mn, Co etc,), these are efficient choices for bifunctional ORR/OER catalyst due to high activity and less expensive nature of transition metals [6-8]. Among the rare earth metal based perovskites, the lanthanides based perovskite material LaCrO3 (LCO) exhibit cubical symmetry with melting point of 2400°C is most important, Because of distinctive electrical, chemical and thermal properties LaCrO3 is much suitable contender for high temperature device applications for example; solid oxide fuel cells [9], sensors [10], membranes [11], catalysis [12] and like others. Moreover, the effects of ambient parameters and doping transition metals on structural and electrical properties are still under consideration by the researchers. Another Lanthanide based perovskite is LaMnO3 (LMO), typically with ABO3-type crystal structure has been studied enormously as electrode material in super capacitors because of their capability to store charge at the vacant sites both for cationic and oxygen via intercalation and/ or reversible faradaic redox reactions [13-18]. The major concern of these perovskite type super capacitor electrodes are low conductivities [19] and short life rounds [16]. The properties of LaMnO3 based electrode material can be improved in two ways. Firstly, by partial substitution of A and/or B site cations through doping [14–16, 20] for example, Wang et al. [16] found that substituting Sr at La site in LaMnO3 through Sr doping exalted the strength and capacitance of LaMnO3. Later one is modulation in stoichiometry of the oxygen site that plays vital role in determination of physical properties of LaMnO3 perovskites [21, 22]. The available cheap computational resources and adequate models based on density functional theory (DFT) for computation of rational material characteristics offer opportunities to probe the
behavior of lanthanides based perovskite theoretically for various advanced device fabrication applications without performing expensive experiments [23-25]. In this study, we report the comprehensive computational theoretical study on structural, thermoelectric, electronic and magnetic properties of LaYO3 (Y= Cr and Mn) perovskites by implementing modified BeckeJohnson (mBJ) potentials, which result in material properties, which agrees with the experiments. 2. Computational details In the ongoing study of La-perovsites, the calculation based on density functional theory (DFT) are finis by Wein2K code handling with FP-LAPW+lo method [26] to investigate the structural, thermoelectric, electronic and magnetic properties of LaYO3 (Y= Cr and Mn) perovskites. We employed the recently evolved modified Becke Johnson (mBJ) potential which precisely measures band structure (BS) of understudy perovskites. With the help of PBEsol generalized gradient approximation [27], the entirely relaxed structures have been optimized in order explore the ground state parameters. The PBEsol-GGA is quite accurate in determining the lattice constant, yet not suitable for the accurate and precise calculation of the band gap. Consequently, we used mBJ potential to evaluate exchange-correlation potentials [28] for electronic properties. The mBJ is versatile and accurate potential which approve the band gap of the studied materials up to experimental values. It is convent, easy and accurate potential than other approaches like GGA+U and LDA+U etc. Furthermore, it can be applicable for ferromagnetic, insulators and semiconductors, while GGA+U/LDA+U are limited to ferromagnetic type systems [29, 30]. To determine the relativistic effects among atomic states in the lattice, the core states and valence states are estimated relativistically by scalar relativistic approximation (SRA). In ferromagnetic (FM) characteristic nature of La-perovskites the spin-orbit (SO) couplings have insignificant effects. The parameter RMT×Kmax is taken to be 8, where Kmax represent plane wave cut-off and RMT being the least radius of the MT spheres. In order to realize the convergence inside the MT sphere expansion up to lmax= 10 is made. However, in case of Fourier expansion of charge density upto Gmax= 16 is taken. Both ferromagnetic and anti-ferromagnetic interactions are optimized by estimating the total energy in contrast to volume of the unit cell to indicate ferromagnetic state stability. For computing the self-consistent field (SCF), the MT sphere expansion was restricted to converge to 1000 k-points because above this the MT sphere started
to distort. The SCF were reiterated until the total energy difference between the subsequent iterations trimmed to 10-5Ry per supercell. 3. Results and Discussion: 3.1 Structural Properties The crystal framework LaYO3 (Y= Cr and Mn) perovskites exhibit cubic structure with space group Pm-3m. The crystal creation of under study materials LaYO3 (Y= Cr and Mn) is such like the six oxygen atoms surround the Cr/Mn atom which takes up center position in the unit cell. These nearby oxygen atoms are located at the face of the unit cell whilst the La ion stays at the corner (see Fig. 1a). To investigate the structural arrangements of cubic LaYO3 (Y= Cr and Mn) perovskites, Brich-Murnghan equation [31] is applied to reduce the total energy of crystals corresponding to volume of unit cell in accordance with our previous work [24]. The equilibrium structural parameters i.e. lattice constant a0 (Å), bulk modulus B0 (GPa) and enthalpy of formation ∆H (eV) measured by GGA-PBEsol are listed in Table 1 for LaYO3 (Y= Cr and Mn) perovskites. These values agree very well with available theoretical and empirical data [32, 33, 34]. To check the ferromagnetic stability of the studied perovskites, structural optimizations have been performed for the cubic structures of the LaYO3 (Y= Cr and Mn) perovskites materials as shown in Fig. 1b for the ferromagnetic (FM), anti-ferromagnetic (AFM) along with nonmagnetic (NM). For this reason, these two studied perovskites are generally thought to be FM, AFM along with NM step by step and at the same time considering each magnetic phase within their super-cells. In addition, the difference of energy equation in between ∆𝐸1 = 𝐸𝐴𝐹𝑀 − 𝐸𝐹𝑀 and ∆𝐸2 = 𝐸𝑁𝑀 − 𝐸𝐹𝑀 produces a positive outcome, which unveils that there is a lot more energy of ferro-magnets suggesting the stableness with the ferromagnetic state which is demonstrated in Table 1. Positive value associated with ∆𝐸1 and ∆𝐸2 signifies the studied perovskites tend to be stable along with ferromagnetic state. Consequently, all other properties, for example magnetic and thermoelectric conduct are also produced using the ferromagnetic state. The evaluation of ground state energies exhibits that greater energy is released during FM state, which assures the stableness of the researched materials inside FM state. To verify the stability
of the LaYO3 (Y= Cr and Mn) perovskites within the FM state, the enthalpy of formation is also measured by using the relation [35], ∆𝐻 = 𝐸𝑡𝑜𝑡𝑎𝑙 (𝐿𝑎𝑌𝑂3 ) − 𝐸𝐿𝑎 − 𝐸𝑌 − 𝐸𝑂
(1)
The negative value of ∆𝐻 (see Table 1) produced for LaYO3 (Y= Cr and Mn) also affirms the stableness of the FM state. 3.2 Electronic and Magnetic Properties To analyze the electronic properties of the cubic LaYO3 (Y=Cr, Mn) perovksites, the spinpolarized self-consistence calculations are performed. Fig. 2 represents the electronic band structure (BS) of Cr/ Mn based La-perovskites, across the highly symmetric axis from the first Brillouin Zone (BZ), the left-panel shows up spin (↑) orientation and the right-panel shows down spin (↓) orientation. The spin up(↑) channel for both the studied materials demonstrates the energy states ranging between -7.4 eV to 0 eV are coming from 3d-states of Y=Cr, Mn with tiny share regarding 2p-states of O2 and f-states of La. Consequently, five d-states associated with Cr/Mn originate for the spin up orientation, which boosts the energy in spin up state and reduces the energy in spin down state. Zhang et al. [36] reported the equivalent spin pattern that leads towards the larger Curie temperature that is also verified by the experiments [37]. The band structure (BS) analysis of LaCrO3 perovskite material showed that it is ferromagnetic semiconductor this is because in spin up orientation the valance band maxima just touches the Fermi level and the bandgap observed in the spin down orientation. However, the BS analysis of LaMnO3 perovskite revealed that LaMnO3 exhibit half-metallic (HM) nature because in the spin up state valence band crosses the Fermi level and bandgap is located in the opposite spin i.e. spin down state. The energy bandgap for the spin down channel exposed the HM characteristic of the LaMnO3 materials. The computed values of the energy bandgaps along with band structure energies are given in Table 2. The HM gap (gh) is referred to as the greater/smaller amongst the highest/lowest values of energies from the conduction/valance bands with regards to the Fermi energy of spin up as well as spin down states respectively [38]. The values of gh are deducted by using the mBJ potential that is also demonstrated in Table 2.
The plots of the density of states for the total compounds and individual atoms of LaYO3 (Y=Cr, Mn) are are illustrated in Fig. 3 and Fig. 4 respectively, and the states are treated as ferromagnetic. For the LaCrO3 perovskite, the total density of states plots (see Fig. 3) demonstrates that the semiconducting pattern is observed for both spin states, because there is energy gap is found across the Fermi level. The trend is slightly changing for the LaMnO3 perovskite material. It is HM in nature because for the up spin state the electrons crossed the Fermi level. Moreover, in the down spin state there is band gap found. Therefore, it can be concluded that LaCrO3 is a ferromagnetic semiconductor whereas LaMnO3 is a HM ferromagnetic compound. It is observed that for both the spin channels difference in energy states of studied La-perovskites (LaCrO3 and LaMnO3) indicate that the magnetic rare earth cations Cr/Mn interacts with anions i.e. oxygen and introduces the exchange splitting
instates. The 3d-statesof Cr/Mn atoms
stationed at octahedral position (VO6) within the unit cell breaks off into five degenerate states owing to crystal field furnished by the electrostatic domains of oxygen. The degeneracy in these states is removed at high energies by lifting the nonlinear doublet states i.e. eg (dz2, dx2-y2) in contrast to linear triplet states i.e. t2g (dxy, dyz, dzx). The nonlinear doublet states further splits up by levitating dx2-y2 rather than dz2 also the triplet states splits by raising dxy over dyz, dzx states as a consequence of John Teller distortions, which elongate the states towards easy axes. Thereby, introducing ferromagnetism in the pervoskites under studied. The hybridization is mediated by unpaired electrons of 3d-states and 2p states of Cr/Mn and O respectively. Fig. 3 represents the PDOS for LCO. From Fig.3, it is observed that the 3d-states of Cr+2 interacts weakly with the 2pstates of O-2 inside the energy range of -5.4 eV to 0 eV for valence band. Moreover, in the up spin channel the conduction states hybridize weakly between 2.8 eV to 6 eV, while for down spin channel this range varies by 2 eV to 3.5eV. Fig. 4 represents the PDOS calculated for LaMnO3. From Fig. 4, it can be seen that for LaMnO3 perovskite the 3d-states of Mn+2 cations weakly interacts with 2p-states of O-2 anions for -7.6 to -2.5 eV energy values and interact strongly from - 1 eV to 1 eV. For the up spin channel strong interaction among states is from 0 eV to 2 eV values of energies, while in case of down spin channel there is feeble interaction from 0 eV to 5 eV. A very minute contribution from s-states of cations with oxygen is identified which confirms that the p-d coupling is more dominant over s-d coupling.
The magnetic behavior of studied perovskites is because of the collective contribution of the constituent species and the crystal field. The resultant magnetic moment (B) imparts from the partially filled d-states of Mn/Cr atoms and the presence of interstitial sites make contributions also [39]. Table 2 reveals the detailed ferromagnetic interactions for LaCrO3 and LaMnO3 in terms of their local magnetic moment. Table 2 shows that major part of B is conferred mainly by Mn/Cr in conjunction with minor contribution that arises from the nonmagnetic La and O atoms and interstitial sites. However, the shortfall in the total B of Mn/Cr is because of strong pd coupling thereby inducing small B at non-magnetic and interstitial sites as well [40]. Furthermore, the positive sign of La magnetic moment allocates that the induced magnetic polarization to be parallel with Mn/Cr. Furthermore, the splitting effect of crystal field energy (i.e. ΔEcrystal =Et2g - Eeg) that arised from the electrostatic contact of the neighboring anions was quantified to explain the observed magnetism. Table 2 is also listed with the values of exchange splitting energies i.e. both direct Δx(d) and indirect Δx(pd), along with the exchange constants that depends on the splitting of valence (ΔEC) and conduction (ΔEV) band edge. Interestingly it is observed that Δx(d)>ΔEcrystal for LaCrO3 and LaMnO3 which reveals that the viewed ferromagnetic state is primarily stabilized by the process of hybridization and hence induces a gross exchange splitting. This effect is further confirmed by estimating Δx(pd), by finding energy differences between the maxima of valence band in both spin channels which are composed mainly by p-states of anions in PDOS. The negative value of Δx(pd) favors ferromagnetism and demonstrates that the spin down channel is highly tempting [40]. Moreover, in regard to comprehensive research associated with
ferromagnetism,
the
edge
splitting
∆𝐸𝑉 = 𝐸𝑉↓ − 𝐸𝑉↑ /∆𝐸𝐶 = 𝐸𝐶↓ − 𝐸𝐶↑
of
the
valance/conduction bands also needs to be measured that help to examine exchange constants by using subsequent equations: 𝑁𝑜𝛼 = ∆𝐸𝐶 /𝑥 < 𝑆 > and 𝑁𝑜𝛽 = ∆𝐸𝑉 /𝑥 < 𝑆 > in which 𝑥 and < 𝑆 > symbolizes the particular content level of Cr/Mn inside the materials as well as the level of magnet moment of Cr/Mn at octahedral placement, respectively. Generally, increased value of 𝑁𝑜𝛽 would results in reduction of energy of the system. Consequently, the system energy is decreased due to the effect of the bond broadening within the spin down state, which is in accordance with Zenger’s exchange type and confirms the magnetism within studied materials [41-43].
3.3 Thermo-electric Properties Time developing energy requirements attracted big pursuits to think about materials, which show excellent thermoelectric effectiveness to comprehend clean energy. Thermoelectric materials have the ability to regulate wasted heat energy using an electric tool, in addition, to creating electrical power, therefore, delivering numerous probabilities to decide on the desired practical application. The thermoelectric properties are usually achievable by means of semiconductors, semimetals, composites etc. For that reason, we also calculated thermoelectric measures related to LaYO3 (Y=Cr, Mn) perovskite materials to show the significance of these materials by means of exhibiting their multifunctional characteristics. Considering that the cation deviation of La can tune the band gap, this is often a really fragile parameter to the demonstrated thermoelectric characteristics. These analyzed perovskites LaYO3 (Y=Cr, Mn) are generally elaborated over the inclusive examination of electrical conductivity(𝜎/𝜏), thermal conductivity(𝜅/𝜏),, and the Seebeck coefficient (𝑆 = ∆𝑉/∆𝑇) as well as electrical power component (𝑃 = 𝜎𝑆 2 ) through BoltzTrap code determined by semi-classical theory [44]. The evaluated results for the thermal parameters of studied materials in the temperature array of 200K to 800K are offered through Fig. 5(a-d). From Fig. 5(a), it is apparent that the value of σ comprises of 0.5× 1019(Ωm s)-1 and 27×1019(Ωms)-1 during 200K pertaining to LaYO3 (Y=Cr, Mn) compounds. After this, for the LaMnO3 perovskite material, on increasing values of temperature upto 800K, the value of σ droped whereas, for the LaCrO3 perovskite, electrical conductivity slightly increases. Furthermore, the σ of LaMnO3 is greater than LaCrO3 which can be as a result of the introduction of extra shells of electrons relating to LaMnO3. As a result, by using additional electron shells, nucleus hold to valence electrons will become delicate and results in conduction electrons to get free. Inside the semiconductor materials, lattice vibrations (phonons) in addition to electrons promote this conduction practice about temperature range active in the product. Fourier regulation 𝑞 = −𝑘 𝑑𝑇/𝑑𝑥 is used to calculate the thermal conductivity of these studied materials. In the above expression q indicates the flux related to heat that is the flow of temperature per system for every system span, dT/dx implies the temperature gradient and к symbolizes the thermal conductivity. The computed value of k for the perovskites LaCrO3 and LaMnO3 is displayed in Fig. 5(b). With raising temperature, the value of k is observed to
increase and achieves its optimum value at 800K. The temperature gradient (∆T) takes place when two different materials touches each other and the electrons flow by means of higher to lesser region of temperatures, which intern advances the potential difference (∆V). To analyze the efficiency of thermocouple, Seeback coefficient (S) is computed. The determined negative value of S suggests that the electrons tend to mediate the conduction procedure and its value decreases as the temperature increases, which can be seen directly through Fig. 5(c). Since the calculated electronic band structure exhibit HM character that is solely mediated by free electrons due to crossing of conduction band states through EF, thereby giving S negative sign. Therefore, the electronic properties confirmed the accuracy of the calculated thermoelectric variables [45]. As a result, the inverse relationship between electrical conductivity and S assure that investigated material LaCrO3 is ferromagnetic semiconductors where as LaMnO3 is halfmetallic ferromagnet. The power factor (σS2) is the cooperative effect of σ and S. Usually σ and S have opposite trends in magnetic materials. The S makes the potential gradient with respect to temperature which minimizes the flow of carriers while the σ enhances the flow of carriers [46]. The calculated plots of σS2 are presented in Fig 5(d). Its value lowers by 0.4 W/mK2S and then increases to 3.2 W/mK2S for LaCrO3 at 800K and for LaMnO3, it values is 0.2 W/mK2S at 200K, with increasing temperature it value increase upto 300K and then decreases. Consequently, through decreasing values of the σ in addition to increasing values of the S and k with the rise of temperature demonstrates that the studied perovskites tend to be ideal for thermoelectric device applications. In summary, the studied Lanthanide-based perovskites reveal that LaCrO3 is a ferromagnetic semiconductor, whereas, LaMnO3 is HF ferromagnetic and exhibit 100% spin polarization making perovskites attractive for spintronic devices. The thermoelectric parameters can also be studied by changing the cationic nature of LaYO3 (Y= Cr and Mn). The thermoelectric trends notify that the studied perovskites excellent behaves at low temperatures can be applied in energy conversion devices. Hence, computed magnetic and thermoelectric parameters reveal that studied perovskites have high potential for technical applications in spintronic and thermoelectric devices.
4. Conclusion In conclusion, PBEsol-GGA and mBJ models based on DFT have been employed to analyze the structural, electronic, magnetic and thermoelectric trends of LaYO3 (Y=Cr, Mn) perovskites. Positive values associated with ∆𝐸1 and ∆𝐸2 signify that the studied perovskites are stable along with ferromagnetic state. The electronic properties illustrated that LaCrO3 material is a ferromagnetic semiconductor, whereas, LaMnO3 is half-metallic ferromagnetic and exhibit100% spin polarization and hence attractive choice for spintronic devices. Furthermore, the greater values of Δx(d) and Δx(pd) as compared to ΔEcrystal for LaCrO3 and LaMnO3 confirmed that the main reason for ferromagnetism is highly carrier concentration. The lessened B of Cr/Mn along with a little B emerging at multiple nonmagnetic sites certifies that the strongly hybridized states mediate ferromagnetism. The thermoelectric trends notify that the LaCrO3 and LaMnO3 excellent behaves at low temperatures, still more explorations are needed to suppress thermal conductivity improve thermoelectric performance. Acknowledgment The authors would like to acknowledge Researcher's Supporting Project Number (RSP-2019/43), King Saud University, Riyadh, Saudi Arabia for their partial support in this work.
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Table 1 The calculated values of a0 (Å), B0 (GPa), total energies differences (∆E1 and ∆E2), ∆H (eV) for LaYO3 (Y=Cr, Mn) perovskites using PBEsol-GGA. Parameters
LaCrO3
Other Cal.
a0(Å) B0(GPa) ∆E1 (meV) ∆E2 (meV) ∆H(eV)
3.91 181.02 32 78 -3.04
3.925c
a
Exp.
LaMnO3
3.888a
3.86 183.45 44 86 -2.89
-3.108c
Other Cal.
Exp.
3.945c
3.904b
-2.948c
[32], b [33], c [34] Table 2
The calculated values of spin down gap (↓Eg (eV)), HM gap (gh (eV)), crystal field energy (ΔEcrystal), direct exchange Δx(d), John-Teller ΔJT(eV) and indirect exchange Δx(pd) energies, total and the local µB (in Bohr magneton) and the exchange constants (Noα and Noβ) for LaYO3 (Y=Cr, Mn) using TB-mBJ potential
c
Parameters
LaCrO3
↓Eg (eV) GHM (ΔEcrystal) Δx(d) ΔJT(eV) Δx(pd) Total (µB) La (µB) Y (µB) O (µB) interstitial (µB) No α No β
3.70 2.86 4.26 1.44 -0.91 3.0000 0.0156 2.5574 0.2464 0.2464 0.078 -0.711
[34]
Other Cal.
3.000c
LaMnO3 3.75 0.15 1.70 4.84 1.35 -3.64 4.0000 0.0139 3.6184 0.2049 0.2049 0.105 -2.01
Other Cal.
4.000c
Fig. 1: (a) Crystal structures of LaYO3 (Y=Cr, Mn) that optimized in FM phase, (b) The volume optimization for LaYO3 (Y=Cr, Mn) perovskites in FM, AFM and NM phases.
Fig. 2: Spin polarized BS plots of LaYO3 (Y=Cr, Mn) perovskites for up spin (↑) channel and down spin (↓) channel.
Fig. 3: The TDOS and PDOS of LaCrO3 perovskite for up spin (↑) channel and down spin (↓) channel.
Fig. 4: The TDOS and PDOS of LaMnO3 perovskite for up spin (↑) channel and down spin (↓) channel.
Fig. 5: Temperature verses (a) electrical conductivity, (b) thermal conductivity, (c) See-beck coefficient and (d) σS2 for LaYO3 (Y=Cr, Mn) perovskites.
Highlights Ab-initio studies to explore physical aspects of Lanthanide-based perovskites LaYO3 (Y= Cr and Mn). The studied perovskites tend to be stable along with ferromagnetic state. The band structure analysis of LaCrO3 perovskite revealed that LaMnO3 exhibit halfmetallic nature. Study of thermoelectric properties show that both perovskites are ideal for thermoelectric device applications.
Graphical Abstract
Figure. Crystal structure of LaYO3 (Y=Cr, Mn) that optimized in FM phase
Deceleration of Interest statement Perovskite oxides betray ABO3 like crystal structure, where site A preserves rare-earth metals (e.g. La, Er, Sm, Dy etc.), while B sites being occupied by transition metals (i.e. V, Ti, Cr, Mn, Co etc,) these are used as efficient choices for bifunctional ORR/OER catalyst. Among the rare earth metal based perovskites, the lanthanides based perovskite material LCO and LMO exhibit cubical symmetry with space group Pm-3m and used for solid oxide fuel cells and sensors. To our knowledge, no theoretical report is available on both perovskite. Therefore, we report the comprehensive computational theoretical study on electronic, magnetic and thermoelectric properties of LCO and LMO perovskites by implementing modified Becke-Johnson (mBJ) potentials, which result in material properties, which agrees with the experiments.
CRediT author statement
Ujala Anwar.: Conceptualization, Methodology, Software, Data curation, Writing- Original draft preparation, Dr. Naveed A. Noor.: Visualization, Investigation, Supervision, Software, Validation. Dr. Asif Mahmood.: Writing- Reviewing and Editing
S0009-2614(19)31012-7 https://doi.org/10.1016/j.cplett.2019.137031 CPLETT 137031
To appear in:
Chemical Physics Letters
Received Date: Revised Date: Accepted Date:
28 September 2019 12 November 2019 7 December 2019
Please cite this article as: N.A. Noor, U. Anwar, A. Mahmood, Investigation of the rare earth-based LaYO3 (Y= Cr and Mn) perovskites by ab-initio approach, Chemical Physics Letters (2019), doi: https://doi.org/10.1016/ j.cplett.2019.137031
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Investigation of the rare earth-based LaYO3 (Y= Cr and Mn) perovskites by ab-initio approach N.A. Noora*, Ujala Anwarb, A. Mahmoodc a
Department of Physics, University of Lahore, Lahore 54000, Pakistan
b
Institute of Chemical Sciences, Bahauddin Zakariya University (BZU), Multan, Pakistan
c
College of Engineering Chemical Engineering Department King Saud University Riyadh, Saudi
Arabia * Corresponding author Email: [email protected] Abstract Here, we report the ab-initio studies to explore physical aspects of Lanthanide-based perovskites LaYO3 (Y= Cr and Mn), using full-potential linearized augmented plane waves logic. The calculated values of lattice constants were 3.91Å and 3.86Å for LaCrO3 and LaMnO3 respectively with PBEsol-GGA, comparable with available experimental data. Band structure and density of states played pivotal role in determination of the electronic properties. Figuring the exchange splitting energies (Δx(d) and Δx (pd)), crystal field energy (ΔCF) and Jahn-Teller energy (ΔJT) traverse the ferromagnetic semiconducting nature of studied La-perovskites. In addition, BoltzTraP code implemented to interrogate the thermoelectric properties. Key Words: Lanthanide-based perovskites, Density functional theory (DFT), ferromagnetic (FM) characteristic, Exchange splitting and Thermoelectric properties,
1. Introduction Perovskite oxide compounds have brought great attention by the researchers as they exhibit wide range of crystal structures [1] and easily tunable physio-chemical and catalytic properties via transition metal doping [2, 3]. Furthermore, the high thermo-chemical stability, electrochemical behavior and ionic conductivity of perovskite oxides make them auspicious for use in industry [4, 5]. Perovskite oxides betray ABO3 like crystal structure, where site A preserves rare-earth metals (e.g. La, Er, Sm, Dy etc.) or alkaline earth metals (e.g. Ca, Sr etc.) while B sites being occupied by transition metals (i.e. Sc, Ti, Cr, Mn, Co etc,), these are efficient choices for bifunctional ORR/OER catalyst due to high activity and less expensive nature of transition metals [6-8]. Among the rare earth metal based perovskites, the lanthanides based perovskite material LaCrO3 (LCO) exhibit cubical symmetry with melting point of 2400°C is most important, Because of distinctive electrical, chemical and thermal properties LaCrO3 is much suitable contender for high temperature device applications for example; solid oxide fuel cells [9], sensors [10], membranes [11], catalysis [12] and like others. Moreover, the effects of ambient parameters and doping transition metals on structural and electrical properties are still under consideration by the researchers. Another Lanthanide based perovskite is LaMnO3 (LMO), typically with ABO3-type crystal structure has been studied enormously as electrode material in super capacitors because of their capability to store charge at the vacant sites both for cationic and oxygen via intercalation and/ or reversible faradaic redox reactions [13-18]. The major concern of these perovskite type super capacitor electrodes are low conductivities [19] and short life rounds [16]. The properties of LaMnO3 based electrode material can be improved in two ways. Firstly, by partial substitution of A and/or B site cations through doping [14–16, 20] for example, Wang et al. [16] found that substituting Sr at La site in LaMnO3 through Sr doping exalted the strength and capacitance of LaMnO3. Later one is modulation in stoichiometry of the oxygen site that plays vital role in determination of physical properties of LaMnO3 perovskites [21, 22]. The available cheap computational resources and adequate models based on density functional theory (DFT) for computation of rational material characteristics offer opportunities to probe the
behavior of lanthanides based perovskite theoretically for various advanced device fabrication applications without performing expensive experiments [23-25]. In this study, we report the comprehensive computational theoretical study on structural, thermoelectric, electronic and magnetic properties of LaYO3 (Y= Cr and Mn) perovskites by implementing modified BeckeJohnson (mBJ) potentials, which result in material properties, which agrees with the experiments. 2. Computational details In the ongoing study of La-perovsites, the calculation based on density functional theory (DFT) are finis by Wein2K code handling with FP-LAPW+lo method [26] to investigate the structural, thermoelectric, electronic and magnetic properties of LaYO3 (Y= Cr and Mn) perovskites. We employed the recently evolved modified Becke Johnson (mBJ) potential which precisely measures band structure (BS) of understudy perovskites. With the help of PBEsol generalized gradient approximation [27], the entirely relaxed structures have been optimized in order explore the ground state parameters. The PBEsol-GGA is quite accurate in determining the lattice constant, yet not suitable for the accurate and precise calculation of the band gap. Consequently, we used mBJ potential to evaluate exchange-correlation potentials [28] for electronic properties. The mBJ is versatile and accurate potential which approve the band gap of the studied materials up to experimental values. It is convent, easy and accurate potential than other approaches like GGA+U and LDA+U etc. Furthermore, it can be applicable for ferromagnetic, insulators and semiconductors, while GGA+U/LDA+U are limited to ferromagnetic type systems [29, 30]. To determine the relativistic effects among atomic states in the lattice, the core states and valence states are estimated relativistically by scalar relativistic approximation (SRA). In ferromagnetic (FM) characteristic nature of La-perovskites the spin-orbit (SO) couplings have insignificant effects. The parameter RMT×Kmax is taken to be 8, where Kmax represent plane wave cut-off and RMT being the least radius of the MT spheres. In order to realize the convergence inside the MT sphere expansion up to lmax= 10 is made. However, in case of Fourier expansion of charge density upto Gmax= 16 is taken. Both ferromagnetic and anti-ferromagnetic interactions are optimized by estimating the total energy in contrast to volume of the unit cell to indicate ferromagnetic state stability. For computing the self-consistent field (SCF), the MT sphere expansion was restricted to converge to 1000 k-points because above this the MT sphere started
to distort. The SCF were reiterated until the total energy difference between the subsequent iterations trimmed to 10-5Ry per supercell. 3. Results and Discussion: 3.1 Structural Properties The crystal framework LaYO3 (Y= Cr and Mn) perovskites exhibit cubic structure with space group Pm-3m. The crystal creation of under study materials LaYO3 (Y= Cr and Mn) is such like the six oxygen atoms surround the Cr/Mn atom which takes up center position in the unit cell. These nearby oxygen atoms are located at the face of the unit cell whilst the La ion stays at the corner (see Fig. 1a). To investigate the structural arrangements of cubic LaYO3 (Y= Cr and Mn) perovskites, Brich-Murnghan equation [31] is applied to reduce the total energy of crystals corresponding to volume of unit cell in accordance with our previous work [24]. The equilibrium structural parameters i.e. lattice constant a0 (Å), bulk modulus B0 (GPa) and enthalpy of formation ∆H (eV) measured by GGA-PBEsol are listed in Table 1 for LaYO3 (Y= Cr and Mn) perovskites. These values agree very well with available theoretical and empirical data [32, 33, 34]. To check the ferromagnetic stability of the studied perovskites, structural optimizations have been performed for the cubic structures of the LaYO3 (Y= Cr and Mn) perovskites materials as shown in Fig. 1b for the ferromagnetic (FM), anti-ferromagnetic (AFM) along with nonmagnetic (NM). For this reason, these two studied perovskites are generally thought to be FM, AFM along with NM step by step and at the same time considering each magnetic phase within their super-cells. In addition, the difference of energy equation in between ∆𝐸1 = 𝐸𝐴𝐹𝑀 − 𝐸𝐹𝑀 and ∆𝐸2 = 𝐸𝑁𝑀 − 𝐸𝐹𝑀 produces a positive outcome, which unveils that there is a lot more energy of ferro-magnets suggesting the stableness with the ferromagnetic state which is demonstrated in Table 1. Positive value associated with ∆𝐸1 and ∆𝐸2 signifies the studied perovskites tend to be stable along with ferromagnetic state. Consequently, all other properties, for example magnetic and thermoelectric conduct are also produced using the ferromagnetic state. The evaluation of ground state energies exhibits that greater energy is released during FM state, which assures the stableness of the researched materials inside FM state. To verify the stability
of the LaYO3 (Y= Cr and Mn) perovskites within the FM state, the enthalpy of formation is also measured by using the relation [35], ∆𝐻 = 𝐸𝑡𝑜𝑡𝑎𝑙 (𝐿𝑎𝑌𝑂3 ) − 𝐸𝐿𝑎 − 𝐸𝑌 − 𝐸𝑂
(1)
The negative value of ∆𝐻 (see Table 1) produced for LaYO3 (Y= Cr and Mn) also affirms the stableness of the FM state. 3.2 Electronic and Magnetic Properties To analyze the electronic properties of the cubic LaYO3 (Y=Cr, Mn) perovksites, the spinpolarized self-consistence calculations are performed. Fig. 2 represents the electronic band structure (BS) of Cr/ Mn based La-perovskites, across the highly symmetric axis from the first Brillouin Zone (BZ), the left-panel shows up spin (↑) orientation and the right-panel shows down spin (↓) orientation. The spin up(↑) channel for both the studied materials demonstrates the energy states ranging between -7.4 eV to 0 eV are coming from 3d-states of Y=Cr, Mn with tiny share regarding 2p-states of O2 and f-states of La. Consequently, five d-states associated with Cr/Mn originate for the spin up orientation, which boosts the energy in spin up state and reduces the energy in spin down state. Zhang et al. [36] reported the equivalent spin pattern that leads towards the larger Curie temperature that is also verified by the experiments [37]. The band structure (BS) analysis of LaCrO3 perovskite material showed that it is ferromagnetic semiconductor this is because in spin up orientation the valance band maxima just touches the Fermi level and the bandgap observed in the spin down orientation. However, the BS analysis of LaMnO3 perovskite revealed that LaMnO3 exhibit half-metallic (HM) nature because in the spin up state valence band crosses the Fermi level and bandgap is located in the opposite spin i.e. spin down state. The energy bandgap for the spin down channel exposed the HM characteristic of the LaMnO3 materials. The computed values of the energy bandgaps along with band structure energies are given in Table 2. The HM gap (gh) is referred to as the greater/smaller amongst the highest/lowest values of energies from the conduction/valance bands with regards to the Fermi energy of spin up as well as spin down states respectively [38]. The values of gh are deducted by using the mBJ potential that is also demonstrated in Table 2.
The plots of the density of states for the total compounds and individual atoms of LaYO3 (Y=Cr, Mn) are are illustrated in Fig. 3 and Fig. 4 respectively, and the states are treated as ferromagnetic. For the LaCrO3 perovskite, the total density of states plots (see Fig. 3) demonstrates that the semiconducting pattern is observed for both spin states, because there is energy gap is found across the Fermi level. The trend is slightly changing for the LaMnO3 perovskite material. It is HM in nature because for the up spin state the electrons crossed the Fermi level. Moreover, in the down spin state there is band gap found. Therefore, it can be concluded that LaCrO3 is a ferromagnetic semiconductor whereas LaMnO3 is a HM ferromagnetic compound. It is observed that for both the spin channels difference in energy states of studied La-perovskites (LaCrO3 and LaMnO3) indicate that the magnetic rare earth cations Cr/Mn interacts with anions i.e. oxygen and introduces the exchange splitting
instates. The 3d-statesof Cr/Mn atoms
stationed at octahedral position (VO6) within the unit cell breaks off into five degenerate states owing to crystal field furnished by the electrostatic domains of oxygen. The degeneracy in these states is removed at high energies by lifting the nonlinear doublet states i.e. eg (dz2, dx2-y2) in contrast to linear triplet states i.e. t2g (dxy, dyz, dzx). The nonlinear doublet states further splits up by levitating dx2-y2 rather than dz2 also the triplet states splits by raising dxy over dyz, dzx states as a consequence of John Teller distortions, which elongate the states towards easy axes. Thereby, introducing ferromagnetism in the pervoskites under studied. The hybridization is mediated by unpaired electrons of 3d-states and 2p states of Cr/Mn and O respectively. Fig. 3 represents the PDOS for LCO. From Fig.3, it is observed that the 3d-states of Cr+2 interacts weakly with the 2pstates of O-2 inside the energy range of -5.4 eV to 0 eV for valence band. Moreover, in the up spin channel the conduction states hybridize weakly between 2.8 eV to 6 eV, while for down spin channel this range varies by 2 eV to 3.5eV. Fig. 4 represents the PDOS calculated for LaMnO3. From Fig. 4, it can be seen that for LaMnO3 perovskite the 3d-states of Mn+2 cations weakly interacts with 2p-states of O-2 anions for -7.6 to -2.5 eV energy values and interact strongly from - 1 eV to 1 eV. For the up spin channel strong interaction among states is from 0 eV to 2 eV values of energies, while in case of down spin channel there is feeble interaction from 0 eV to 5 eV. A very minute contribution from s-states of cations with oxygen is identified which confirms that the p-d coupling is more dominant over s-d coupling.
The magnetic behavior of studied perovskites is because of the collective contribution of the constituent species and the crystal field. The resultant magnetic moment (B) imparts from the partially filled d-states of Mn/Cr atoms and the presence of interstitial sites make contributions also [39]. Table 2 reveals the detailed ferromagnetic interactions for LaCrO3 and LaMnO3 in terms of their local magnetic moment. Table 2 shows that major part of B is conferred mainly by Mn/Cr in conjunction with minor contribution that arises from the nonmagnetic La and O atoms and interstitial sites. However, the shortfall in the total B of Mn/Cr is because of strong pd coupling thereby inducing small B at non-magnetic and interstitial sites as well [40]. Furthermore, the positive sign of La magnetic moment allocates that the induced magnetic polarization to be parallel with Mn/Cr. Furthermore, the splitting effect of crystal field energy (i.e. ΔEcrystal =Et2g - Eeg) that arised from the electrostatic contact of the neighboring anions was quantified to explain the observed magnetism. Table 2 is also listed with the values of exchange splitting energies i.e. both direct Δx(d) and indirect Δx(pd), along with the exchange constants that depends on the splitting of valence (ΔEC) and conduction (ΔEV) band edge. Interestingly it is observed that Δx(d)>ΔEcrystal for LaCrO3 and LaMnO3 which reveals that the viewed ferromagnetic state is primarily stabilized by the process of hybridization and hence induces a gross exchange splitting. This effect is further confirmed by estimating Δx(pd), by finding energy differences between the maxima of valence band in both spin channels which are composed mainly by p-states of anions in PDOS. The negative value of Δx(pd) favors ferromagnetism and demonstrates that the spin down channel is highly tempting [40]. Moreover, in regard to comprehensive research associated with
ferromagnetism,
the
edge
splitting
∆𝐸𝑉 = 𝐸𝑉↓ − 𝐸𝑉↑ /∆𝐸𝐶 = 𝐸𝐶↓ − 𝐸𝐶↑
of
the
valance/conduction bands also needs to be measured that help to examine exchange constants by using subsequent equations: 𝑁𝑜𝛼 = ∆𝐸𝐶 /𝑥 < 𝑆 > and 𝑁𝑜𝛽 = ∆𝐸𝑉 /𝑥 < 𝑆 > in which 𝑥 and < 𝑆 > symbolizes the particular content level of Cr/Mn inside the materials as well as the level of magnet moment of Cr/Mn at octahedral placement, respectively. Generally, increased value of 𝑁𝑜𝛽 would results in reduction of energy of the system. Consequently, the system energy is decreased due to the effect of the bond broadening within the spin down state, which is in accordance with Zenger’s exchange type and confirms the magnetism within studied materials [41-43].
3.3 Thermo-electric Properties Time developing energy requirements attracted big pursuits to think about materials, which show excellent thermoelectric effectiveness to comprehend clean energy. Thermoelectric materials have the ability to regulate wasted heat energy using an electric tool, in addition, to creating electrical power, therefore, delivering numerous probabilities to decide on the desired practical application. The thermoelectric properties are usually achievable by means of semiconductors, semimetals, composites etc. For that reason, we also calculated thermoelectric measures related to LaYO3 (Y=Cr, Mn) perovskite materials to show the significance of these materials by means of exhibiting their multifunctional characteristics. Considering that the cation deviation of La can tune the band gap, this is often a really fragile parameter to the demonstrated thermoelectric characteristics. These analyzed perovskites LaYO3 (Y=Cr, Mn) are generally elaborated over the inclusive examination of electrical conductivity(𝜎/𝜏), thermal conductivity(𝜅/𝜏),, and the Seebeck coefficient (𝑆 = ∆𝑉/∆𝑇) as well as electrical power component (𝑃 = 𝜎𝑆 2 ) through BoltzTrap code determined by semi-classical theory [44]. The evaluated results for the thermal parameters of studied materials in the temperature array of 200K to 800K are offered through Fig. 5(a-d). From Fig. 5(a), it is apparent that the value of σ comprises of 0.5× 1019(Ωm s)-1 and 27×1019(Ωms)-1 during 200K pertaining to LaYO3 (Y=Cr, Mn) compounds. After this, for the LaMnO3 perovskite material, on increasing values of temperature upto 800K, the value of σ droped whereas, for the LaCrO3 perovskite, electrical conductivity slightly increases. Furthermore, the σ of LaMnO3 is greater than LaCrO3 which can be as a result of the introduction of extra shells of electrons relating to LaMnO3. As a result, by using additional electron shells, nucleus hold to valence electrons will become delicate and results in conduction electrons to get free. Inside the semiconductor materials, lattice vibrations (phonons) in addition to electrons promote this conduction practice about temperature range active in the product. Fourier regulation 𝑞 = −𝑘 𝑑𝑇/𝑑𝑥 is used to calculate the thermal conductivity of these studied materials. In the above expression q indicates the flux related to heat that is the flow of temperature per system for every system span, dT/dx implies the temperature gradient and к symbolizes the thermal conductivity. The computed value of k for the perovskites LaCrO3 and LaMnO3 is displayed in Fig. 5(b). With raising temperature, the value of k is observed to
increase and achieves its optimum value at 800K. The temperature gradient (∆T) takes place when two different materials touches each other and the electrons flow by means of higher to lesser region of temperatures, which intern advances the potential difference (∆V). To analyze the efficiency of thermocouple, Seeback coefficient (S) is computed. The determined negative value of S suggests that the electrons tend to mediate the conduction procedure and its value decreases as the temperature increases, which can be seen directly through Fig. 5(c). Since the calculated electronic band structure exhibit HM character that is solely mediated by free electrons due to crossing of conduction band states through EF, thereby giving S negative sign. Therefore, the electronic properties confirmed the accuracy of the calculated thermoelectric variables [45]. As a result, the inverse relationship between electrical conductivity and S assure that investigated material LaCrO3 is ferromagnetic semiconductors where as LaMnO3 is halfmetallic ferromagnet. The power factor (σS2) is the cooperative effect of σ and S. Usually σ and S have opposite trends in magnetic materials. The S makes the potential gradient with respect to temperature which minimizes the flow of carriers while the σ enhances the flow of carriers [46]. The calculated plots of σS2 are presented in Fig 5(d). Its value lowers by 0.4 W/mK2S and then increases to 3.2 W/mK2S for LaCrO3 at 800K and for LaMnO3, it values is 0.2 W/mK2S at 200K, with increasing temperature it value increase upto 300K and then decreases. Consequently, through decreasing values of the σ in addition to increasing values of the S and k with the rise of temperature demonstrates that the studied perovskites tend to be ideal for thermoelectric device applications. In summary, the studied Lanthanide-based perovskites reveal that LaCrO3 is a ferromagnetic semiconductor, whereas, LaMnO3 is HF ferromagnetic and exhibit 100% spin polarization making perovskites attractive for spintronic devices. The thermoelectric parameters can also be studied by changing the cationic nature of LaYO3 (Y= Cr and Mn). The thermoelectric trends notify that the studied perovskites excellent behaves at low temperatures can be applied in energy conversion devices. Hence, computed magnetic and thermoelectric parameters reveal that studied perovskites have high potential for technical applications in spintronic and thermoelectric devices.
4. Conclusion In conclusion, PBEsol-GGA and mBJ models based on DFT have been employed to analyze the structural, electronic, magnetic and thermoelectric trends of LaYO3 (Y=Cr, Mn) perovskites. Positive values associated with ∆𝐸1 and ∆𝐸2 signify that the studied perovskites are stable along with ferromagnetic state. The electronic properties illustrated that LaCrO3 material is a ferromagnetic semiconductor, whereas, LaMnO3 is half-metallic ferromagnetic and exhibit100% spin polarization and hence attractive choice for spintronic devices. Furthermore, the greater values of Δx(d) and Δx(pd) as compared to ΔEcrystal for LaCrO3 and LaMnO3 confirmed that the main reason for ferromagnetism is highly carrier concentration. The lessened B of Cr/Mn along with a little B emerging at multiple nonmagnetic sites certifies that the strongly hybridized states mediate ferromagnetism. The thermoelectric trends notify that the LaCrO3 and LaMnO3 excellent behaves at low temperatures, still more explorations are needed to suppress thermal conductivity improve thermoelectric performance. Acknowledgment The authors would like to acknowledge Researcher's Supporting Project Number (RSP-2019/43), King Saud University, Riyadh, Saudi Arabia for their partial support in this work.
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Table 1 The calculated values of a0 (Å), B0 (GPa), total energies differences (∆E1 and ∆E2), ∆H (eV) for LaYO3 (Y=Cr, Mn) perovskites using PBEsol-GGA. Parameters
LaCrO3
Other Cal.
a0(Å) B0(GPa) ∆E1 (meV) ∆E2 (meV) ∆H(eV)
3.91 181.02 32 78 -3.04
3.925c
a
Exp.
LaMnO3
3.888a
3.86 183.45 44 86 -2.89
-3.108c
Other Cal.
Exp.
3.945c
3.904b
-2.948c
[32], b [33], c [34] Table 2
The calculated values of spin down gap (↓Eg (eV)), HM gap (gh (eV)), crystal field energy (ΔEcrystal), direct exchange Δx(d), John-Teller ΔJT(eV) and indirect exchange Δx(pd) energies, total and the local µB (in Bohr magneton) and the exchange constants (Noα and Noβ) for LaYO3 (Y=Cr, Mn) using TB-mBJ potential
c
Parameters
LaCrO3
↓Eg (eV) GHM (ΔEcrystal) Δx(d) ΔJT(eV) Δx(pd) Total (µB) La (µB) Y (µB) O (µB) interstitial (µB) No α No β
3.70 2.86 4.26 1.44 -0.91 3.0000 0.0156 2.5574 0.2464 0.2464 0.078 -0.711
[34]
Other Cal.
3.000c
LaMnO3 3.75 0.15 1.70 4.84 1.35 -3.64 4.0000 0.0139 3.6184 0.2049 0.2049 0.105 -2.01
Other Cal.
4.000c
Fig. 1: (a) Crystal structures of LaYO3 (Y=Cr, Mn) that optimized in FM phase, (b) The volume optimization for LaYO3 (Y=Cr, Mn) perovskites in FM, AFM and NM phases.
Fig. 2: Spin polarized BS plots of LaYO3 (Y=Cr, Mn) perovskites for up spin (↑) channel and down spin (↓) channel.
Fig. 3: The TDOS and PDOS of LaCrO3 perovskite for up spin (↑) channel and down spin (↓) channel.
Fig. 4: The TDOS and PDOS of LaMnO3 perovskite for up spin (↑) channel and down spin (↓) channel.
Fig. 5: Temperature verses (a) electrical conductivity, (b) thermal conductivity, (c) See-beck coefficient and (d) σS2 for LaYO3 (Y=Cr, Mn) perovskites.
Highlights Ab-initio studies to explore physical aspects of Lanthanide-based perovskites LaYO3 (Y= Cr and Mn). The studied perovskites tend to be stable along with ferromagnetic state. The band structure analysis of LaCrO3 perovskite revealed that LaMnO3 exhibit halfmetallic nature. Study of thermoelectric properties show that both perovskites are ideal for thermoelectric device applications.
Graphical Abstract
Figure. Crystal structure of LaYO3 (Y=Cr, Mn) that optimized in FM phase
Deceleration of Interest statement Perovskite oxides betray ABO3 like crystal structure, where site A preserves rare-earth metals (e.g. La, Er, Sm, Dy etc.), while B sites being occupied by transition metals (i.e. V, Ti, Cr, Mn, Co etc,) these are used as efficient choices for bifunctional ORR/OER catalyst. Among the rare earth metal based perovskites, the lanthanides based perovskite material LCO and LMO exhibit cubical symmetry with space group Pm-3m and used for solid oxide fuel cells and sensors. To our knowledge, no theoretical report is available on both perovskite. Therefore, we report the comprehensive computational theoretical study on electronic, magnetic and thermoelectric properties of LCO and LMO perovskites by implementing modified Becke-Johnson (mBJ) potentials, which result in material properties, which agrees with the experiments.
CRediT author statement
Ujala Anwar.: Conceptualization, Methodology, Software, Data curation, Writing- Original draft preparation, Dr. Naveed A. Noor.: Visualization, Investigation, Supervision, Software, Validation. Dr. Asif Mahmood.: Writing- Reviewing and Editing