First-principles investigation of structural, electronic, optical and thermal properties of Zinc doped SrTiO3

Journal Pre-proof First-principles investigation of structural, electronic, optical and thermal properties of Zinc doped SrTiO3 S.S.A. Gillani, Riaz Ahmad, Islah-u-din, Muhammad Rizwan, M. Shakil, Muhammad Rafique, G. Murtaza, H.B. Jin

PII:

S0030-4026(19)31379-8

DOI:

https://doi.org/10.1016/j.ijleo.2019.163481

Reference:

IJLEO 163481

To appear in:

Optik

Received Date:

22 June 2019

Accepted Date:

24 September 2019

Please cite this article as: Gillani SSA, Ahmad R, Islah-u-din, Rizwan M, Shakil M, Rafique M, Murtaza G, Jin HB, First-principles investigation of structural, electronic, optical and thermal properties of Zinc doped SrTiO3 , Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163481 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

First-principles investigation of structural, electronic, optical and thermal properties of Zinc doped SrTiO3 S. S. A. Gillania*, Riaz Ahmada, Islah-u-dina, Muhammad Rizwanb, M. Shakilb, Muhammad Rafiqueb, G. Murtazac, H. B. Jind a

Department of Physics, Government College University Lahore, Lahore 54000, Pakistan Department of Physics, University of Gujrat, Gujrat 50700, Pakistan c Centre for Advanced Studies in Physics, Government College University Lahore, Lahore, 54000, Pakistan d School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, PR Chin b

*

Corresponding author: [email protected]

Abstract

ro of

This work reports the first-principles study, based on the density functional theory (DFT), by using generalized gradient approximation (GGA) and ultra-soft pseudo-potential (USP), to explore effects of zinc (Zn) doping on structural, electronic, optical and thermal properties of cuboctahedral SrTiO3. We observe significant reduction in unit cell volume upon doping Zn

-p

into SrTiO3. Furthermore, Zn doping introduces new sates at Brillouin zone symmetry points turning the indirect band gap of host material into direct one. Replacement of Zn with Sr in

re

host lattice repositions density of states at lower energies resulting in stronger interactions between Zn-atom and its neighbors as compared to interactions between Sr-atom and its

lP

surroundings. This refers to substantial modification in electronic band structure of host material by Zn doping. Physical properties of SrTiO3 also change significantly upon Zn doping in accordance with the electronic band structure. Significant changes in electronic

na

structure and properties of SrTiO3 by Zn doping opens new prospects for potential applications of these materials in optoelectronics. Keywords:

ur

SrTiO3, Electronic properties, Density of states, Thermal properties, Optoelectronic

Jo

applications

1. Introduction The general formula for perovskite is ABX3 and represent the ternary compound, where two different cations are A and B, contribute with equal ratio, and X is anion. Perovskites have wide range of applied science applications like waveguides, electro-optics, extent computer memory cells, magnifying laser frequency, etc. [1–4]. The most important perovskite from the titanate family is strontium titanate SrTiO3 (STO). Potential and useful applications of pure and doped STO are as: fuel cells anodes [5], sensors [6], photo-catalysis

to hydrolyses [7, 8], a substrate for growing yttrium barium copper oxide superconductors [9], super-lenses [10], medicine for orthopaedic drug administration [11], capacitors [12, 13], varistors [14] and reversible electronic switching in computers [15]. Structure of STO is comprehend by corner participating octahedra having titanium (Ti) at the middle of each

ro of

octahedron TiO6 (Fig. 1a).

-p

Fig. 1. Ideal cubic Pm3m structure of STO, Ti centered (left-blue), Sr centered (right-green) and O (red).

The gaps between eight octahedra groups are filled by the strontium (Sr) and SrO12

re

cuboctahedra is formed (Fig. 1b). The cubic phase of STO is quite simple with apical symmetry having Pm3m space group and 0.3905nm lattice parameter at room temperature

lP

[16, 17]. This symmetry phase is seen above its transition temperature range 105.5 - 110K [16, 18–22]. Titanium and strontium atoms are positioned at the mid of oxygen octahedra and cuboctahedra, respectively. A pair of nearby Ti-atoms are exactly intersected by every

na

oxygen atom. Two Ti-atoms (0.2nm) and four Sr-atoms (0.28nm) are tightly bounded by each oxygen atom. The volume of the cuboctahedral is greater (≈ 5 times) than the volume of octahedral volume. This elucidates the positions of cations Sr (large) and Ti (small) at A and

ur

B sites of ABX3, respectively.

At room temperature the reported band gap of STO is 3.20eV and shows insulating behavior

Jo

[23]. Without applying an external electric field STO can split the water into its constituents [24–27]. Although the band gap with large value needs ultraviolet radiation (UV), which is around 3% of the solar spectrum. Approaches to repress this issue are the partial addition of impurity, Cu, Zn, Nb, Mg, on cation sites and by decreasing the anion content. Due to this conductivity and photocatalytic activity can be enhanced and even physical properties such as thermal, electrical and optical properties are customized, essential for application point of view [28]. Due to vast applications of STO the both experimental [29] and theoretical [30]

studies of pure, doped and co-doped STO are going on. Doping of Zn at cation sites tunes its band gap. But by doing the deep literature study of pure and doped STO, we have not found enough literature of Zn doped STO, either theoretically or experimentally, in detail for the understanding of physical properties. Literature are only available on the photocatalytic property of Zn doped STO [31–33]. With the substitution of transition metal (TM) and carries doping in the experiment some of the new STO photocatalysts have been recently investigated. This includes Zn doped STO and BaTiO3 [34, 35], (TM: Mn, Fe, Co)-doped STO [36, 37], Cr doped STO [38], Nb and La doped STO [39]. Photocatalytic activity of Zn doped STO, prepared by sol-gel method, have

ro of

been reported [35] and reveals phenomenal enhancement in efficiency of H2 production than that of pure STO. Study of the Ag doped STO revealed that inside the band gap some unaccompanied impurities occur, although in case of Pb doped STO shifting of the VB to higher energies was examined and host material band gap compressed and appeared in the

-p

visible light region [40]. Photocatalytic-activity also enhanced by nitrogen (N) doping in STO

re

and thus visible light absorbance marked up with increase in N content in STO [41–44].

In this work, physical properties such as structural, electronic, thermal and optical properties have been examined in detailed for un-doped and Zn doped, Zn cation favors to position at

lP

Sr-site [35], STO cuboctahedra with DFT using GGAPBE function. For deep understanding this approach is quite constructive. The lattice parameters and band gap tuning of Zn doped

na

STO are examined. We have observed a small variation in the lattice constant of Zn doped STO and linked to evolution of new states at G-(gamma) points. With Zn addition, the band gap exhibits a substantial change, and this may be happened due to the interactivity of the Zn

ur

d-orbitals. Due to this response of band gap, it would be a promising contestant for device application. With doping of Zn, we have also observed a red shift in the optical properties of

Jo

STO.

The layout of the paper is: In Section II the computational detail along with band structure (BS) interpretation and methodology is explained, in Section III results are discussed by dividing it into three subsections. At the end section IV concludes our findings.

2. Computational details

As we have already mentioned, at room temperature, cubic structure of STO belongs to space group Pm3m (Fig. 1). For present study, in case of pure STO, the calculated lattice constants (a = b = c) of STO

are

comparable

the

experimentally

value

0.3906nm [45].

-p

ro of

measured

to

0.3944nm,

re

Fig. 2. Supercell of Zn doped SrTiO3.

To understand influence of Zn-doping in the absence of boundary effects, Zn-atom is

lP

individually incorporated in STO at Sr sites and simulations were executed on 2 × 2 × 1 supercell as shown in Fig. 2. We have executed all the simulations by applying CASTEP

without

na

code [47, 48] build on DFT by considering planewave-pseudopotential approach [49], approximation

of

the

orbital’s

shape.

For

the

exchange-correlation

potential, in the generalized gradient approximation (GGA), the Perdew-Burke-Ernzerhof

ur

(PBE) parametrization is applied [50, 51]. Nuclei and electrons interactions are approximated by Vanderbit ultra-soft pseudo potential (USPP) by considering valence states Sr: 4s2 4p6 5s2,

Jo

Ti: 4s1 3d3, O: 2s2 2p4 and Zn: 4s2 3d10. Residual forces were below 2meV = A0 for relaxation of atomic positions and lattice constants. With cut-off energy of 340eV, the wave functions of electrons are unfolded in terms of discrete plane-wave basis [52]. For pure and doped STO the k-points meshes of Brillouin zone sampling were fixed at 2 × 2 × 1 established on Monkhorst Pack grid. To get the single point energy, geometry is optimized at first, and convergence accuracy, in the self-consistent energy, has been taken as 5 × 10-5eV/atom. All calculations have been performed after optimization of geometry.

3.

Results

and

discussion

3.1. Optimization of geometry and structural parameters After the improvisation of 2 × 2 × 1 supercell the modified geometry parameters, with GGAPBE [50, 51], for pure STO is obtained i.e. a = b = c = 0.3944nm and correlated with experimental and theoretical literature values [45, 46, 53–56] (Tab. 1). Our calculated value is nearly same as the already reported results and this shows the quality of our first principles calculations. In next, the same procedure is repeated for the Zn doped STO. We observed a

ro of

very small difference (0.0016) in the lattice parameters of pure and Zn doped STO and hence the size of the doped unit cell is bit smaller than pure STO. This small difference is due to different ionic radii of Sr and Zn.

Table 1: Geometry optimization and unit cell parameters of SrZrO3. The theoretical and experimental results

-p

from literature are also given for comparison.

Lattice parameters (A0)

Structure Methodology

b

re

a

3.86

na

Experimental pure [45, 46]

ur

Cubic

Jo

DFT present study pure DFT present study doped

3.86

57.512

3.95

3.95

3.95

61.629

3.93

3.93

3.93

60.698

3.85

3.85

3.85

57.066

3.90

3.90

3.90

59.319

3.89

3.89

3.89

58.863

3.94

3.94

3.94

61.349

3.92

3.94

3.94

60.605

3.2. Electronic properties of pure and Zn-doped SrTiO3 3.2.1. Pure SrTiO3

(A3)

3.86

lP

DFT reported pure [53-56]

c

Volume

To examine the effects of Zn-doping in the electronic band structure of STO, we have first

ro of

computed the band structure, total density of states (TDOS) and partial density of states

(PDOS) of pure STO and are plotted in Fig. 3(a, b) and Fig. 4(a). Figure 3(a) shows the band

-p

structure of pure STO.

re

Fig. 3. Energy band Structure (a) and TDOS (b) of pure SrTiO3.

It is clearly seen that the conduction band (CB) minima lies at G-symmetry point, while the

lP

maxima of the valence band (VB) is at R symmetry point. By considering these two symmetry points the computed bandgap (R-G: indirect band gap) is 1.792eV, and comparable

Jo

ur

na

values of band gap are also reported in the literature [57, 58].

Fig. 4. PDOS of pure (a) and Zn doped (b) SrTiO3. Vertical line indicates the Fermi level.

For R-G band gap the electrons transition from VB to CB occurs through phonons and consequently due to these transitions’ incident energy is partially dissipated. This may lead to minimize the efficiency of opto-electronic materials synthesized by STO. By means of outstanding constraints of GGA computed band gap is typically undervalue in comparison with experimentally measured value 3.20eV. If we consider the symmetry point G for both CB minima and VB maxima, then we get the value of direct (G-G) band gap which is

ro of

2.152eV. The value of G-G band gap is greater than R-G bandgap and still smaller than the experimental value [23]. This is due to anion and cation pd repulsion whereas GGA is performed [59]. Figure. 4a expresses the PDOS and from this we can clearly see that O-2pstates contribute majorly in VB top and 3d-states of Ti play main role in the bottom of CB.

-p

3.2.2. Zinc doped SrTiO3

To explore the influence of the Zn-atom addition in STO, on the cost of Sr atom, on the

re

electronic properties of STO, the band structure, TDOS and PDOS of Zn doped STO are devised in Fig. 5(a, b) and Fig. 4(b), respectively. The computed band structure along with

lP

TDOS of doped STO is depicted in Fig. 4a, b. Due to this VB is shifted towards Fermi level

Jo

ur

na

and its maxima and CB minima are passed through symmetry point G.

Fig. 5. Energy band Structure (a) and TDOS (b) of Zn doped SrTiO3.

This reveals that transformation of R-G band to G-G band. Change of band gap nature explains a significant basis that photo-catalytic action and photoconductivity, with light brilliance, will be intensified in comparison with pure STO. The value of doped STO band gap is 1.443eV and 0.349eV is the difference between un-doped and doped STO. Zn doped PDOS imply that valence bands top is largely be expressed by O-2p-orbital, at the same time Zn-3d-orbital and Ti-3d-orbital are contributed to conduction bands bottom (Fig. 4b). Besides, the findings of band gap reduction and behavior of PDOS are in line with the optical properties results (Fig. 6). From the above discussion, on the grounds of the crystal structure and electronic properties, this can summarize that Zn doping at Sr site is subjected for

3.3. Optical Properties of pure and Zn doped SrTiO3

ro of

absorption edge red shift as well as the modification of the band structure.

In order to determine the electronic band structure quantitatively, optical methods are quite effective. Experiments on refraction, transmission and optical reflectivity anticipate the

-p

approach to find the dielectric constant (epsilon) of the solid that associated with the band structure. Such properties have substantial value to understand the emerging physical

re

properties and their benefits in prospective applications. In the range of linear optical response, function related to the optical properties of a solid, on macroscopic level, is

lP

revealed by the dielectric function. This is well known fact that electronic feedback is coupled along the dielectric function. By using complex dielectric function ε(ω) = ε1(ω) + i ε2(ω) the optical properties of pure and Zn doped STO were determined. Here ε1(ω) and

na

ε2(ω) represents the real and complex part of DE function. By using the Kramers-Kronig transformation the ε1(ω) was estimated from ε2(ω). ε2(ω) itself was estimated by using

ur

momentum matrix elements bounded by the wave functions of occupied and unoccupied states by applying the selection rules. The reflectivity, absorption and electron energy-loss

Jo

functions were extracted via the computed dielectric functions. The dielectric function ε1(ω) and ε2(ω) parts as function of the incident photon energy for pure STO and Zn doped STO are depicted in Fig. 6(a, b). At 0eV photon energy, the ε2(ω) is also zero for un-doped and doped STO. This indicates that no energy is dissipated. In the spectra of ε2(ω), we observed main peaks at energies of 4.13, 7.26, 23.02 and 36.30eV for pure STO and at the nearly same values of energies we have absorption peaks (Fig. 6c). For doped STO, we have similar pattern of ε2(ω) and absorption spectra but with slight increase in the above-mentioned values (Fig. 6b). ε2(ω) peaks are associated to inter-band transition

from VB to CB and only these transitions, 2p-O to 3d-Ti and 4d-Sr, played a role and have angular momentum under selection rule i.e. ∆l = ±1. ε2(ω) peaks cannot be occurred due to a single inter-band transition because one can find number of indirect transitions in band

re

-p

ro of

structure with an energy relating to the same peaks [60].

Fig. 6. Detailed optical analysis of pure (black) and Zn doped (blue) SrTiO 3. Real DF (a) and imaginary DF (b).

lP

Absorption spectra (c), loss function (d), reflectivity (e) and refractive index (f).

Absorption spectra, of both pure and doped system, have main peaks nearly at the same energies, where ε2(ω) have, as shown in Fig. 6(c). The most intensified absorption peak for

na

pure and doped system is around at 23.81eV and consequently less amount of photon energy is dissipated (Fig. 5b). For Zn doped SrTiO3 the absorption edge shifts to low energy and this effect may be an evidence of the reduction of band gap (Fig. 3a).

ur

The frequency dependent complex refractive index has two parts: refractive index (n) and extinction coefficient (k). For pure and Zn doped STO the value of n is 2.45 and 2.68,

Jo

respectively. The value of n for doped system is slightly greater than the value of n for undoped system. This is may be an indication of the conversion of the semiconductor STO to metallic STO. These values of n at 0eV are related with the lowest value of absorbed energy. Graph of n shows decreasing trend with increase in photon energy whereas the spectrum of the absorbed energy shows the increasing trend (Fig. 6c, f). The annihilation of energy within the system is described by the k and is related with spectrum of absorbed energy (Fig. 7). Both the k and the absorption spectrum remain in line for pure and doped system. This means

that when k indicates the increasing trend then absorption also shows the same trend and vice versa. The observed peaks in energy loss function serve as the characteristic’s energies, where the electrons are not bound to lattice sites, linked with the plasma resonance and the related frequency is known as plasma frequency [61]. For the un-doped system, a sharp peak related to plasma oscillation is observed at 27.46eV, whereas for doped system this peak is shifted to lower energy 26.91eV (Fig. 6d). The higher value of ε2(ω) is related with the minimum value energy

loss

function. This is the

vital feature of the

semiconductors. In the

same way we have

observed

reflection points

spectra

minimum

(Fig.

reflection is to be absorption

is

6c).

ur

na

lP

re

-p

then

the

(Fig. 6e) that all the

where

maximum

from

ro of

of

Fig. 7. (Colors online) Extinction coefficient of pure (black) and Zn doped (blue) SrTiO3.

Jo

3.4. Thermoelectric Properties of pure and Zn doped SrTiO3 For energy renewable device applications, the thermoelectric materials have remarkable importance because heat energy is lost in many energies generating and consuming devices. The efficiency of the devices depends upon the figure of merit (ZT) i.e. the ratio of electrical to thermal conductivity must be small. In this subsection we have presented the calculated thermoelectric properties (ZT, electrical conductivity (σ/τ), thermal conductivity (K), Seebeck coefficient (S)) of pure and Zn doped STO in the temperature range of 0-800K and are shown

in Fig. 8(a-d). From electrical conductivity we can estimate the number of free electrons used for conduction with increase in temperature. Figure 8b shows the electrical conductivity of pure and Zn doped STO. The slope of the curve is high for pure STO as compare to the Zn doped STO. This shows that the less free electrons are available for conduction in Zn doped STO. The electrical conductivity, for both cases, increases with the increase in temperature. The thermal conductivity shows the same behavior as the electrical conductivity as shown in Fig. 8c. The thermal conductivity relies on electronic and phononic contributions [62, 63]. The lattice vibrations of the atoms are increased with the rise in temperature and these

ur

na

lP

re

-p

ro of

vibrations allow the material to conduct heat from one point to another point by convection.

Fig. 8. Thermoelectric analysis of pure (black) and Zn doped (blue) SrTiO 3. Figure of merit (a), electrical

Jo

conductivity (b), thermal conductivity (c) and Seebeck coefficient (d) as a function of temperature 0-800K.

The part of thermal conduction due to lattice vibrations is very small as compare to the electronic part of the thermal conduction. Due to the difference in temperature across the material the potential is induced in the material which defines the Seebeck effect. Figure 8d shows the coefficient of Seebeck (S) which is calculated by the expression S = ∆V/∆T, here ′V′ is induced potential and ′T′ is the temperature. At temperature of 50K, the value of S for pure and doped STO is around 8.4 (μV/K), as the temperature is increased up to 150K the value of S is increased for pure STO and is decreased for Zn doped STO. Our calculated

results indicate that with further increase in temperature the S for Zn doped STO represents increasing trend in complete temperature range and while pure STO shows decreasing trend up to around 350K and then increasing trend. In the last, we have also calculated the figure of merit (ZT) in order to see the thermoelectric efficiency (Fig. 8a). ZT curves are obtained by taking the ratio of electrical conductivity to the thermal conductivity i.e. ZT = σS2/KT in which the ratio should be minimum and strongly suggests the studied material for

ro of

thermoelectric applications.

4. Conclusion

In the present work we have presented the detailed results of the structural, electronic, optical, and thermal properties with Zn-doping in the cuboctahedra structure of SrTiO3. All

-p

the results were computed by applying the density functional theory within the approach of GGA-PBE. Our computed structural parameters agree with literature results and are

re

discussed in line of Zn-doping. The band structure of pure SrTiO3 gives the indirect bandgap and it is transformed to direct bandgap, with the emergence of new states at G-point, after Zn-

lP

doping. After doping, we have also observed the shifting of the Fermi level towards conduction band. Emergence of new states at G-point lead to the reduction of bandgap in doped system as compare to pure SrTiO3. Electronic band structure results also revealed that

na

in TDOS the 3d-Ti, 3d-Zn and 2p-O orbitals play vital role in the bottom of conduction band and the top of the valance band, respectively. The study of the PDOS indicate that 3d-Ti, 3dZn states are more active, along with blend of 5S -Sr-states, in the conduction band and 2p-O-

ur

states are dominated in the valence band. Finally, the complex dielectric function, absorption spectra, reflectivity and energy-loss spectra and thermal properties were calculated for both

Jo

pure and doped system. Slight shifting (red shift) of absorption edge to lower energies was also observed upon doping. The relations of the optical properties to the inter-band transitions were also discussed. Acknowledgements One of the author S. S. A. Gillani would like to thank the Office of Research Innovation and Commercialization (ORIC) of GC University Lahore, Pakistan for financial support under the grant number 186/ORIC/18.

References

ro of

[1] C. Noguera, Physics and Chemistry at Oxide Surfaces, Cambridge University Press, New York, (1996).

[2] V.E. Henrick, P.A. Cox, The Surface Science of Metal Oxides, Cambridge University Press, New York, (1994).

Materials, Clarendon Press, Oxford, (1977).

-p

[3] M.E. Lines, A.M. Glass, Principles and Applications of Ferroelectrics and Related

re

[4] O. Auciello, J. F. Scott, R. Ramesh, The Physics of Ferroelectric Memories, Phys. Today 51 7 (1998) 22.

lP

[5] Q. Ma, F. Tietz, D. Sebold, and D. Stover, Y-Substituted SrTiO3-YSZ Composites as Anode Materials for Solid Oxide Fuel Cells: Interaction Between SYT and YSZ, Journal of

na

Power Sources, 195 (2010) 1920.

[6] J. Gerblinger and H. Meixner,” Fast Oxygen Sensors Based on Sputtered Strontium

ur

Titanate”, Sensors and Actuators B4, (1991) 99. [7] J. G. Mavroides, J. A. Kafalas, and D. F. Kolesar, Photoelectrolysis of Water in Cells with

Jo

SrTiO3 Anodes, Applied Physics Letters, 28 (1976) 241. [8] F. T. Wagner and G. A. Somorjai, Photocatalytic and Photoelectrochemical Hydrogen Production on Strontium Titanate Single Crystals, Journal of the American Chemical Society, 102 (1980) 5494.

[9] S. A. Hayward and E. K. H. Salje, Cubic-Tetragonal Phase Transition in SrTiO3 Revisited: Landau Theory and Transition Mechanism, Phase Transitions, 68 (1999) 501.

[10] S. C. Kehr, Y. M. Liu, L. W. Martin, P. Yu, M. Gajek, S.-Y. Yang, C. H. Yang, M. T. Wenzel, R. Jacob, H.-G. von Ribbeck, M. Helm, X. Zhang, L. M. Eng, and R. Ramesh, NearField Examination of Perovskite-Based Superlenses and Superlens-Enhanced Probe-Object Coupling, Nature Communications, 2 (2011) 249. [11] Y. Xin, J. Jiang, K. Huo, T. Hu, and P. K. Chu, Bioactive SrTiO3 Nanotube Arrays: Strontium Delivery Platform on Ti-Based Osteoporotic Bone Implants, ACS Nano, 3 (2009) 3228. [12] Y. S. Ham and J.-H. Koh, The Dielectric Characteristics of Screen Printed SrTiO3 Epoxy

ro of

Composite Thick Films on the Cu Plate PCB Substrates, Ferroelectrics, 382 (2009) 85. [13] C. Jorel, C. Vallee, P. Gonon, E. Gourvest, C. Dubarry, and E. Defay, High Performance Metal-Insulator-Metal Capacitor Using a SrTiO3-ZrO2 Bilayer, Applied Physics Letters, 94 (2009) 253502.

-p

[14] Y. Nakano and N. Ichinose, Oxygen Adsorption and VDR Effect in (Sr, Ca) TiO3 Based Ceramics, Journal of Materials Research, 5 (1990) 2910.

re

[15] T. Menke, R. Dittmann, P. Meuffels, K. Szot, and R. Waser, Impact of the Electroforming Process on the Device Stability of Epitaxial Fe Doped SrTiO3 Resistive

lP

Switching Cells, Journal of Applied Physics, 106 (2009) 114507. [16] F. W. Lytle, X-Ray Diffractometry of Low-Temperature Phase Transformations in

na

Strontium Titanate, Journal of Applied Physics, 35 (1964) 2212. [17] H. Kronmuller and S. Parkin, Handbook of Magnetism and Advanced Magnetic Materials, Wiley, vol. 4 (2007), (contains article: M. Johnsson and P. Lemmens,

ur

Crystallography and Chemistry of Perovskites). [18] S. V. Bogdanov, A. M. Kashtanova, and K. V. Kiseleva, Concerning the Phase

Jo

Transitions in SrTiO3, English (translation), Bulletin, Academy of Sciences of the USSR, 29 (1965) 902.

[19] M. A. Saifi and L. E. Cross, Dielectric Properties of Strontium Titanate at Low Temperature, Physical Review B 2 (1970) 677. [20] K. A. Muller and W. Berlinger, Static Critical Exponents at Structural Phase Transitions, Physical Review Letters, 26 (1971) 13.

[21] W. G. Nilsen and J. G. Skinner, Raman Spectrum of Strontium Titanate, The Journal of Chemical Physics, 48 (1968) 2240. [22] H. Unoki and T. Sakudo, Electron Spin Resonance of Fe3+ in SrTiO3 with Special Reference to the 110K Phase Transition, Journal of the Physical Society of Japan, 23 (1967) 546. [23] F. Ernst, O. Kienzle, M. Ruhle, Structure and composition of grain boundaries in ceramics, J. Eur. Ceram. Soc. 19 (1999) 665. [24] M. Cardona, Phys. Rev., 140 (1965) A651.

ro of

[25] Y. Xu and M. A. A. Schoonen, Am. Mineral., 85 (2000) 543.

[26] D. Wang, J. Ye, T. Kako and T. Kimura, J. Phys. Chem. B 110 (2006) 15824.

[27] H. Yu, S. Ouyang, S. Yan, Z. Li, T. Yu and Z. Zou, J. Mater. Chem. 21 (2011) 1347.

-p

[28] S. Suzuki, T. Yamamoto, H. Suzuki, K. Kawaguchi, K. Takahashi, Y. Yoshisato, Fabrication and characterization of Ba1-xKxBiO3/Nb doped SrTiO3 all-oxide-type Schottky

re

junctions, J. Appl. Phys. 81 (1997) 6830.

[29] T. Jarlborg, tuning of the electronic screening and electron-phonon coupling in doped

lP

SrTiO3 and WO3, Phys. Rev. B 61 (2000) 9887.

[30] Y. Tokura, Y. Taguchi, Y. Okada, Y. Fujishima, T. Arima, K. Kumagai, Y. Iye, Filling

na

dependence of electronic properties on the verge of metal Mott-insulator transition in Sr 1-xLaxTiO3, Phys. Rev. Lett. 70 (1993) 2126. [31] Wang Gui-yun, Qin Ya, Cheng Jie, Wang Yan-ji, Influence of Zn doping on the

ur

photocatalytic property of SrTiO3, J. of Fuel Chem. and Tech. 38 (2010) 4. [32] Jian-Ping Zou, Long-Zhu Zhang a, Sheng-Lian Luo, Le-Hui Leng , Xu-Biao Luo ,

Jo

Ming-Jian Zhang, Yan Luo , Guo-Cong Guo, Preparation and photocatalytic activities of two new Zn doped SrTiO3 and BaTiO3 photocatalysts for hydrogen production from water without cocatalysts loading, international journal of hydrogen energy 37 (2012) 17068. [33] M. M. Fadlallah, M. F. Shibl, T. J. H. Vlugt and U. Schwingenschlogl, Theoretical study on cation co-doped SrTiO3 photocatalysts for water splitting, Journal of Materials Chemistry A 6 (2018) 24342. [34] Wang G Y et al, J. Fuel Chem. Technol. 38 (2010) 502.

[35] Zou J P et al, Int. J. Hydrogen Energy 37 (2012) 17068. [36] Li P et al, RSC Adv. 4 (2014) 47615. [37] Zhou X et al, J. Phys. Chem. C 115 (2011) 8305. [38] Cai F et al, RSC Adv. 5 (2015) 21290. [39] Yun J N et al, Chin. Phys. B 19 (2010) 017101. [40] H. Irie, Y. Maruyama, K. Hashimoto, Ag+ and Pb2+ doped SrTiO3 photocatalysts. A correlation between band structure and photocatalytic activity, J. Phys. Chem. C 111 (2007)

ro of

1847. [41] J. Wang, S. Yin, M. Komatsu, Q. Zhang, F. Saito, T. Sato, Preparation and characterization of nitrogen doped SrTiO3 photo-catalyst, J. Photochem. Photobiol. A Chem. 165 (2004) 149.

-p

[42] J. Wang, S. Yin, M. Komatsu, Q. Zhang, F. Saito, T. Sato, Mechanochemical synthesis and photocatalytic activity of nitrogen doped SrTiO3, J. Ceram. Soc. Jpn. 5 (2004) S1408.

re

[43] J. Wang, S. Yin, M. Komatsu, T. Sato, Lanthanum and nitrogen co-doped SrTiO3 powders as visible light sensitive photo-catalyst, J. Eur. Ceram. Soc. 25 (2004) 3207.

Lett. 53 (1984) 2571.

lP

[44] O. K. Anderson Jepsen, O. Explicit, First-principles tight-binding theory, Phys. Rev.

na

[45] Mitchell R H et al, Phys. Chem. Miner. 27 (2000) 583. [46] K. H. Hellwege, A. M. Hellwege (Eds.), Ferroelectrics and Related Substances, New

ur

Series, vol. 3, Landolt-Bornstein, Springer Verlag, Berlin, (1969), group III. [47] Segall M D et al, Z. Kristallogr. 220 (2005) 567.

Jo

[48] M. D. Segall, P.L.D. Lindan, M.J. Probert, C.J. Pickard, P.J. Hasnip, S. J. Clark, M.C. Payne, First principles simulation: ideas, illustrations and the CASTEP code, J. Phys. Condens. Matter 14 (2002) 2717. [49] V. Milman, B. Winkler, J.A. White, C.J. Pickard, M.C. Payne, E.V. Akhmatskaya, R.H. Nobes, Electronic structure, properties, and phase stability of inorganic crystals: a pseudopotential plane-wave study, Int. J. Quantum Chem 77 (2000) 895.

[50] J. P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh, C. Fiolhais Atoms, molecules, solids, and surfaces: applications of the generalized gradient approximation for exchange and correlation, Phys. Rev. B 46 (1992) 6671. [51] J. P. Perdew, K. Bruke, M. Ernzerhof, generalized gradient approximation made simple, Rev. Let. 77 (1996) 3865. [52] C. Tsai, H. Teng, Chromium-doped titanium dioxide thin-film photoanodes in visiblelight induced water cleavage, Appl. Surf. Sci. 254 (2008) 4912.

[54] S. Tinte, M.G. Stachiotti, Phys. Rev. B 58 (1998) 11959.

ro of

[53] R.D. King-Smith, D. Vanderbilt, Phys. Rev. B 49 (1994) 5828.

[55] F. Cora, C. R. A. Catlow, Faraday Discuss. 144 (1999) 421.

[56] G. Cappelini, S. Bouette-Russo, B. Amadon, C. Noguera, F. Finocchi, J. Phys. Condens.

-p

Matter 12 (2000) 3671.

[57] H. Irie, Y. Maruyama, K. Hashimoto, Ag+- and Pb2+-doped SrTiO3 photocatalysts. A

re

correlation between band structure and photocatalytic activity. J. Phys. Chem. C 111 (2007) 1847.

lP

[58] Muhammad Rizwan, Adnan Ali, Zahid Usman, N. R. Khalid, H. B. Jin, C. B. Cao, Structural, electronic and optical properties of copper doped SrTiO3 perovskite: A DFT study, Physica

B:

Condensed

Matter

552

(2019)

52.

na

[59] F.D. Murnaghan, The compressibility of media under extreme pressures, Proc. Natl. Acad. Sci. U. S. A. 30 (1944) 244.

ur

[60] B. Xu, L. Yi, J. Alloy. Compd. 438 (2007) 25. [61] M. Fox, Optical Properties of Solids (Oxford University Press, (2001).

Jo

[62] T. Zhu, K. Swaminathan-Gopalan, K. Stephani, E. Ertekin, Phys. Rev. B 97 (2018) 174201.

[63] C. Boffito, L. Toia, L. Cattaneo, Cesium mixtures and use thereof, United States patent application US 10/842 (2004) 352.