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An ab-initio Study - Universe Publishing Group

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International Journal of Material and Mathe matical Science s, 3(3), 50-59, 2021

Publisher homepage: www.universepg.com, ISSN: 2707-4625 (Online) & 2707-4617 (Print)
https://doi.org/10.34104/ijmms.021.050059
International Journal of Material and Mathematical Sciences
Journal homepage: www.universepg.com/journal/ijmms

The Physical Properties of ThCr2Si2- Type Co-based Compound SrCo2Si2: An ab-initio Study
Md. Shahidul Islam1, Md. Atikur Rahman2* and Nahida Farjana2
1Department of Physics, Tarash Honours College, Tarash, Sirajganj, National University, Gazipur-1704, Bangladesh; 2Departments of Physics, Pabna University of Science and Technology, Pabna-6600, Bangladesh. *Correspondence: [email protected] (Md. Atikur Rahman, Assistant Professor, Departments of Physics, Pabna University of Science and Technology, Pabna-6600, Bangladesh).

ABSTRACT
In this article, we have studied the mechanical, electronic, and optical features of ThCr2Si2- type compound SrCo2Si2. The investigation has been done by using the first-principles method depend on the density functional theory (DFT) and the calculations were completed with the Cambridge Serial Total Energy Package (CASTEP) code. The optimized lattice parameters are well in accord with the existing synthesized values. The investigated elastic constants for this compound are positive which ensured the mechanical stability of this phase. The calculated values of Pugh’s ratio and Poisson’s ratio ensure the brittle character of SrCo2Si2. The universal anisotropic constant AU ensures the anisotropic behavior of SrCo2Si2.The softness nature of SrCo2Si2 is confirmed by the bulk modulus calculations. The overlapping of the valence band and conduction band near the Fermi level indicates the metallic nature of SrCo2Si2. At the Fermi level the major contribution comes from Co-3d and Si-3p states. The large reflectivity in the high-energy region indicates that this compound might be useful as coating materials for reducing solar heating. The photoconductivity and absorption begin with zero photon energy which also ensures the metallic nature of SrCo2Si2.

Keywords: Co-based compound SrCo2Si2, Structural properties, Electronic properties, and Optical properties.

1. INTRODUCTION:
ThCr2Si2 type ternary intermetallic materials usually hold a superconducting ground position. The rareearth AM2X2 structural materials have received great interest of researchers because of their many rich characteristics. Recently AM2X2 (where, A is a lanthanide element or any alkaline earth element; M is any transition metal; X = P, Ge, Si or As) type compounds have achieved great interest having their many interesting features such as mixed valiancy, superconductivity at both high and low temperature, valence fluctuation and heavy fermions behavior (Stewart, 2001). These types of transition metal with AM2X2 type structure confirm extremely goodlooking and wealthy physics in view of the fact that of their close energies relating to the spin, charge
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and orbital motion (Imada et al., 1998). There are more than two thousand classes of ternary inter metallic compounds (Villars and Genzual, 2007) which are essentially obtained from the BaAl4 type structures. Among these classes ThCr2Si2 type compounds were first discovered and illustrated in 1965 by Ban and Sikirica, (1965). A complete and acceptable geometric assessment of about six hundred phases of ThCr2Si2 type structures are represented by Just and Paufler, (1996).
In recent times ThCr2Si2- type structure has gained massive consideration of researchers after discovering a new superconductor (Ba0.6K0.4) Fe2As2 belongs to the “122” family of iron-arsenide’s with ThCr2Si2 type structure exhibits high transition tem-
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perature 38K (Rotter et al., 2008). On the other hand, Pt, Ni and Pd-based ThCr2Si2 type borocarbides (Nagarajan et al., 1994; Cava et al., 1994; Batlogg et al., 1994) have been discovered in the recent years with the transition temperature up to 23K which raises the hope to constitute a family of new high temperature superconductors. In ironbased compounds, the ternary intermetallic (122type compounds) in the company of ThCr2Si2 type structure as example AFe2As2 (A = Sr, Ca, Ba, etc.) are free from oxygen having metallic nature (Rotter et al., 2008; Sasmal et al., 2008; Torikachvili et al., 2008). These types of compounds have been comprehensively studied for interpreting their superconducting mechanism (Johnston 2010; Stewart 2011). These types of compounds have high chemical flexibility and abundance of substitution possibilities. In recent times concentration was given to a series of the iron based and arsenic-free AeT2X2 compounds (Ae = alkaline earth metal, T = Ni, Pd; X = P, Ge) with very low transition temperatures (Tc ~ 0.3 - 3.0 K) (Mine et al., 2008). Undoped RT2Si2 (R = La, Y, Th; T = Ir, Pt) type superconductors are predicted to CaBe2Ge2-type structures (Yang et al., 2011). However the compounds with alkaline earth metals having ThCr2Si2- type structure inedquate 2009; are (Ronning et al., 2009; Fujii and Sato, 2009; Shelton et al., 1984; Doerrscheidt et al., 1976; Rieger and Parthé, 1969; Bodak and Gladyshevskii, 1968; Palenzona et al., 1987).
In this work we have studied a new phase with alkaline earth metal on the A-site crystallizing in the ThCr2Si2- type structure are inadequate. The compound SrCo2Si2 signifies the third ternary SrT2Si2 compound (T = 3d-block transition metals) besides SrCu2Si2 (Kranenberg et al., 2002) and SrZn2Si2 (May and Schäfer, 1972). For SrT2Si2 the isostructural compounds with T = Pd, Ag have been characterized and reported (Eisenmann et al., 1970). The compound SrCo2Si2 is isoelectronic to the parent Fepnictide superconductors AeFe2As2 at the X site, contrast to their electronic bonding situation will be of special interest. Here we have studied the detailed physical properties of Co-based material SrCo2Si2 by using the DFT based calculations implemented in CASTEP code.
2. Computational details The CASTEP code (Segall et al., 2002) written by FORTRAN 95 language is used to investigate the physical properties of SrCo2Si2. The calculations
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were done by DFT theory within GGA with the PBE exchange-correlation function (Clark et al., 2005; Materials Studio CASTEP, 2010; Hohenberg and Khon, 1964; Perdew et al., 2008). The pseudo atomic calculations were done for Sr-4s2 4p6 5s2, Si3s2 3p2 and Co-3d7 4s2 valence electrons. The plane wave cut-off energy was set to 500 eV. The special k-point sampling of the Brillouin zone (BZ) was employed by using the Monkhorst-Pack method (Monkhorst and Pack, 1976) with special 10×10×10 grid points in the primitive cell of SrCo2Si2. The crystal structure of SrCo2Si2 was optimized by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) minimization technique (Pfrommer et al., 1997). For this optimization the criteria of convergence were set to 1.0×10-5 eV/atom for energy, 0.03 eV/Å for force, 0.05 Gpa for stress and 0.001 Å for ionic displacement. The elastic stiffness constants of SrCo2Si2 were obtained by the stress-strain method (Fan et al., 2006). Then the bulk properties were obtained by the elastic constant data of SrCo2Si2. In that case the criteria of convergence tolerance were set to 2.0×10-6 eV/atom for energy, 2.0×10-4 Å for maximum ionic displacement, 6.0×10-3 eV/Å for maximum ionic force and 0.1 GPA for maximum stress component. The maximum strain amplitude was set to be 0.003 in the present calculation of SrCo2Si2.
3. RESULT AND DISCUSSION: 3.1 Structural properties - At normal temperature and pressure, SrCo2Si2 possesses a tetragonal crystal structure with the space group of I4/mmm (no.139) (Hoffmann et al., 2012). The conventional and optimized crystal structures of SrCo2Si2 are shown in Fig 1. The unit cell contains two formula units (Z=2) with ten atoms that means one formula unit for each primitive cell with five atoms. The atomic position of Sr, Co, and Si in the unit cell of SrCo2Si2 tetragonal crystal are 2a (0 0 0), 4d (0 0.5, 0.25) and 4e (0 0 0.3606) respectively.
Fig 1: The crystal structures of SrCo2Si2 (a) Conventional unit cell (three dimensional); (b)
Primitive cell (two dimensional). 51

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Table 1: The calculated equilibrium lattice parameters, unit cell volume, bulk modulus of ThCr2Si2-type SrCo2Si2 compound in comparison with available experimental data.

Properties
a0 (Å) c0 (Å) c0 /a0 V0 (Å3) B0 (Gpa)

This work 3.939 10.601 2.668 166.9 75.73

SrCo2Si2
Experimental 3.974 10.395 2.616 164.2 80.6

Deviation from Expt. (%)
0.8807 1.982 1.988 1.644 6.042

The unit cell dimensions including equilibrium lattice parameters for tetragonal phase a0 and c0, bulk modulus B0 and the equilibrium cell volume V0 of SrCo2Si2 intermetallics at ambient temperature are charted in Table 1 with the experimentally evaluated values. From Table 1 it is obvious that the calculated lattice parameters are exceedingly close to the experimental data which ensure the dependability of the DFT- based investigations. From Table 1 we have seen that, our calculated lattice parameters are slightly deviated from the experimental results. The motive is due to the temperature dependence of the lattice parameters and GGA route (Zhu et al., 2016).
3.2 Elastic properties - Elastic constants are very vital parameters which help us by providing the information about the nature of force present in a solid material. A proper explanation about the mechanical and dynamical behavior of crystalline solid is provided by the analysis of elastic constants. These properties also ensure the mechanical stability, rigidity

and ductile/brittle nature of a solid material (Golesorkhtabar et al., 2013; Koç et al., 2012). Different important properties of solid materials such as ducti-
lity, anisotropy, stiffness, brittleness and stability can be derived from the elastic constant data (Rahaman et al., 2016). Hence in this article a thorough investigation into the mechanical nature of SrCo2Si2 has been done with accurate discussion and composition. The elastic constants were achieved from a linear fit of the calculated stress-strain function according to
Hook’s law (Nye, 1961). A crystal with the tetragonal phase belongs to six independent elastic constants (C11, C12, C13, C33, C44 and C66).The estimated elastic constants of SrCo2Si2 are listed in Table 2. According to the stability criteria (Pokunov et al., 2004) of tetragonal phase (Eq. 1) the com-pounds under consideration have good stability in nature.

C11>0, C33>0, C66>0, C44>0

C11+C33-2C13>0, C11-C12>0

2(C11+C12) +4C13+C33>0

(1)

Table 2: The evaluated elastic constants Cij (in GPa) of SrCo2Si2 with similar type of compounds

Compounds SrCo2Si2 SrRu2As2
SrRh2Ge2

C11 196.72 181.95
179.5

C12 54.35 57.08
72.4

C13 45.13 48.31
52.2

C33 92.79 120.74
103.6

C44 69.66 49.23
52.6

C66 83.77 70.40
80.9

Ref. This work Chowdhury et al.,
2019 Salma et al., 2018

By utilizing the evaluated data of Cij, the most important mechanical features such as bulk modulus B, shear modulus G, Young’s modulus Y, anisotropy factor A and Poisson’s ratio ν of intermetallic SrCo2Si2 have been calculated by using the VoigtReuss-Hill (VRH) averaging scheme (Hill, 1952). Which are listed in Table 3. The Voigt and Reuss bounds of B and G for cubic systems can be
represented by the following expressions.

𝐵𝑣

=

2𝐶11+2𝐶12+𝐶33+4𝐶13 9

(2)

𝐵𝑅 = 𝐶2⁄𝑀

(3)

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𝐺𝑣 = 𝑀 + 3𝐶11 − 3𝐶12 + 12𝐶44 + 6𝐶66 ⁄30

(4)

𝐺𝑅 = [18𝐵𝑣 +

15 6 +6 + 3]

(5)

𝐶2 (𝐶11−𝐶12) 𝐶44 𝐶66

Where, M and C2 can be written as,

M = C11+C12+2C33-4C13 and C2= (C11+C12) C33-2C132

The arithmetic mean value of the Voigt (BV, GV) and the Reuss (BR, GR) bounds which is used to calculate the polycrystalline modulus is given by in terms of
Voigt-Reuss-Hill approximations:

BH = B =

1 2

(BR

+

Bv)

(6)

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Rahman et al., / International Journal of Material and Mathematical Sciences, 3(3), 50-59, 2021

GH = G =

1 2

(Gv

+

GR)

(7)

Using the following expressions we have also cal-
culated the Young’s modulus (Y) and Poisson’s ratio (ν),

Y = 39BG+BG (8) ν = 23(B3B−+2GG) (9)

The Young’s modulus is specified by the ratio of the tensile stress to tensile strain, which measure the stiffness for solid material. The larger value of Y point outs the more stiffness of a compound (Chen,
et al., 2011). The higher value makes the solid better stiffer. The calculated Young’s modulus is shown in Table 3 along with available similar type of com-
pounds. From Table 3, we can say that the value of Young’s modulus of SrCo2Si2 is larger than SrRu2As2 and SrRh2Ge2 compounds indicating that

the compound SrCo2Si2 is stiffer than SrRu2As2 and SrRh2Ge2 compounds.
The Poisson’s ratio is another useful parameter to understand the nature of bonding force in a material (Cao et al., 2013). The smaller value of ν (ν = 0.1) indicates the covalent materials whereas for ionic
crystal ν = 0.25. The larger value of Poisson’s ratio (𝜈 > 0.26) indicates that the compound will be ductile and the compound will be brittle when the value of Poisson’s ratio is (𝜈 < 0.26). From Table 3, we see that the value of ν is 0.18 which refers the brittle nature of SrCo2Si2. The ratio between bulk and shear modulus (B/G) is known as Pugh’s ratio which is applied to understand the brittleness and ductility manner of solid material (Pugh, 1954).
According to Pugh’s criteria a material should be brittle if it’s B/G<1.75, otherwise it should be ductile. From our calculations we see that B/G<1.75, hence the material SrCo2Si2 shows brittle manner which is very similar to Poisson’s ratio.

Table 3: Evaluated polycrystalline bulk modulus B (GPa), shear modulus G (GPa), Young’s modulus E (GPa), B/G value, Poisson’s ratio v and elastic anisotropy AU of SrCo2Si2 with similar types of compounds.

Compounds

B

G

Y

B/G

v

AU

Ref.

SrCo2Si2

80.60

64.44

152.64

1.25

0.18

0.629

This work

SrRu2As2

86.11

55.03

136.05

1.56

0.23

0.180 Chowdhury et al., 2019

SrRh2Ge2

86.60

54.40

134.70

1.59

0.24

0.469

Salma et al., 2018

The universal anisotropic factor of a solid material is specified by the subsequent relation (Ranganathan, et al., 2008).

AU = 5GGRv + BBvR − 6 (10)
AU = 0 indicates completely isotropic crystal and the deviation from this value shows the degree of anisotropy in a material. Chung and Buessen suggests two new relations (Chung and Buessem, 1967) to determine the anisotropy indexes of bulk modulus and shear modulus given as follows,

𝐴𝐵 = ((𝐵𝐵𝑣𝑣−+𝐵𝐵𝑅𝑅))

(11)

𝐴𝐺 = ((𝐺𝐺𝑣𝑣−+𝐺𝐺𝑅𝑅))

(12)

For an isotropic crystal the value of A is 1 and for anisotropic crystal the values of A are either smaller or greater than unity. From Table 3 we see that the value of A is less than unity which represents the anisotropic nature of this compound.

3.3 Electronic properties - The band structure and density of states (TDOS and PDOS) provide a clear concept about the electronic properties of a material. The electronic band structure provides vital information about a material to be metal, semiconductor or insulator. The bonding features of a material are obtained from the partial and total density of states calculations (Hu, et al., 2014). The full picture of energy bands and band gaps of a solid is known as electronic band structure or simply band structure. In solid-state and condensed matter physics, the band structure defines certain ranges of energy that are allowed for electrons within a solid, and the ranges of energy that are not allowed for any electrons. The investigated band structure for SrCo2Si2 has been illustrated in Fig 2 in the energy range -10 eV to 10 eV which is observed along the high symmetry directions in the first Brillouin zone. The horizontal solid line at 0 eV indicates the Fermi level. From band structure it has seen that the valence bands and conduction bands are overlapped at Fermi level and there is no band gap indicating that this compound

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Rahman et al., / International Journal of Material and Mathematical Sciences, 3(3), 50-59, 2021 shows metallic manner. The metallic nature of SrCo2Si2 signifies that this compound might be superconductor. The partial and total density of states of SrCo2Si2 is plotted in Fig 3. From Fig 3 we have observed that the total density of states (TDOS) of SrCo2Si2 is composed of four main peaks.
Fig.5.4(a) Electronic band structure of SrCo2Si2

Fig 2: The band structure of compound SrCo2Si2.
The first peak in the valence band lies between 36.17 eV and -34.75 eV. In SrCo2Si2, Sr-5s states contribute the most to create the first peak. The second peak lies between -18.63 eV and -16.93 eV in SrCo2Si2. This peak is dominated by Co-3d and Si-3p states. The third peak lies between -11.42 eV and -7.46 eV. This peak is contributed by Si-3p states. The fourth peak lies from -6.32 eV to 8.65 eV. This peak is dominated by Si-3s and Si-3p states. We observe clear coincidence between the Co-3d and Si-3p states in SrCo2Si2, which suggests the covalent nature of Co-Si bonds in SrCo2Si2 (Rahman et al., 2016). This is a common feature of ThCr2Si2 type com-pounds (Jeitschko et al., 1987). The calculated DOS at EF is 3.43 states/ eV-unit cell.
3.4 Optical properties - The study of photon energy dependent optical function of a solid material is so essential due to the fact that it helps to get a clear conception concerning the electronic configuration of materials. The optical properties of SrCo2Si2 with different photon energies are calculated by the frequency dependent dielectric function, 𝜀(𝜔) = 𝜀1(𝜔) + 𝑖𝜀2(𝜔), which is closely correlated to the electronic configurations. The imaginary part 𝜀2(𝜔) of dielectric function is obtained from the momentum matrix elements between the filled and the unfilled electronic state by utilizing the subsequent relation (Materials Studio CASTEP, 2010);
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Fig 3: The calculated density of states (TDOS and PDOS) of SrCo2Si2.

  ()  2e2

 c uˆ  r v

2


(Ec



Ev



E)

(13)

2

 0 k,v,c k

k

k

k

Where, ω refers to light frequency, e indicates the electronic charge, uˆ is the vector representing the polarization of the incident electric field, along with
ψkc and ψkv are the conduction band and valence band
wave functions at k, successively. From the imaginary part  the real part 1() of the dielectric function is obtained through the Kramers-Kronig relations.

𝜀1(𝜔)

=

1

+

2 𝜋

𝑃




𝜔′𝜀2(𝜔′) 𝜔′2 − 𝜔2

𝑑𝜔′

0

(14)

Where, 𝜔 denotes the light frequency and 𝑃 refers the principle value of the integral part.

The reflectivity spectra are derived from Fresnel’s formula for normal incidence assuming an orienta-
tion of the crystal surface parallel to the optical axis using the relation (Fox, 2001).

𝑅(𝜔) = |√𝜀(𝜔) − 1|2

(15)

√𝜀(𝜔) + 1

We calculate the absorption coefficient I(ω), the real part of optical conductivity Re[σ(ω)] and the elec-

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tron energy-loss spectrum L(ω) using the following expressions (Delin et al., 1996).
𝐼(𝜔) = √2(𝜔) (√𝜀1(𝜔)2 + 𝜀2(𝜔)2 − 𝜀1(𝜔))1⁄2 (16)

Re[𝜎(𝜔)] = 𝜔𝜀2

(17)

4𝜋

𝐿(𝜔) = 𝜀1(𝜔𝜀)22+(𝜔𝜀)2(𝜔)2

(18)

The optical spectra such as the refractive index,

n(𝜔), and the extinction coefficient, k(𝜔), are easily

calculated in terms of the components of the com-

plex dielectric function as follows:

𝜀1(𝜔) √𝜀1(𝜔)2 + 𝜀2(𝜔)2 1⁄2

(19)

𝑛(𝜔) = [ 2 +

2

]

√𝜀1(𝜔)2 + 𝜀2(𝜔)2 𝜀1(𝜔) 1⁄2

𝑘(𝜔) = [

2

− 2]

(20)

The photon energy dependent ground state optical properties of SrCo2Si2 are shown in Fig 4 in the energy range up to 50 eV along the [100] direction. For optical properties investigation we have used a 0.5ve Gaussain smearing.

energy conversion efficiency and point out the penetration depth of light of precise energy into the material before being absorbed (Ali et al., 2016). For this phase the strong absorption coefficients are observed in the UV region, however, they are weak in the visible region but continuously increase to-ward the UV region, and reach a maximum value at 9.11 eV. This result indicates that this compound is promising for absorbing materials in the UV region.

3.4.1 Reflectivity - Reflectivity is a surface-sensitive analytical technique used in Physics, Chemistry and material science to characterize surfaces, thin films and multi layers. The optical reflectivity spectra are shown in Fig 4(a) as a function of incident photon energy. For SrCo2Si2 the reflectivity spectrum starts with a value of 0.48, at the beginning it decreases and then rises again to reach maximum value of 0.79 at 13.22 eV obtained in the high energy region. This high value of reflectivity in high energy region reveals the characteristics of high conductance in the low energy region (Ali et al., 2016). Hence the compound shows promises as good was coating materials in the ultraviolet region.
3.4.2 Absorption Coefficient - The absorption coefficient visualizes how far into a material light of a particular wave length can penetrate before it is absorbed. The absorption coefficient depends on the material and also on the wavelength of light which is being absorbed. The photon energy dependent absorption spectra of SrCo2Si2 are shown in Fig 4(b). For this compound the absorption spectra starts at zero photon energy which ensures the metallic manner of this phase. This phase exhibit quite good absorption coefficient in the energy ranges 4-22 eV. It supplies the information about the optimum solar
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Fig 4: The optical functions: (a) reflectivity, (b) absorption, (c) refractive index, (d) dielectric
function, (e) conductivity and (f) loss-function of SrCo2Si2 along [100] direction.
3.4.3 Refractive index - Refractive index is a dimensionless quantity which determines how much light is bent or refracted when entering into material (Russell, 2003). The concept of refractive index of optical material is important for use in optical instruments like optical crystals, waveguides etc. Fig 4(c) shows the refractive index of SrCo2Si2 which is one of the important optical properties. In the low energy region the highest refractive index of SrCo2Si2 was found to 6.0 and this value rapidly decreases in the high energy region.
3.4.4 Dielectric function - An important optical function of solid material is the dielectric function which illustrates how an element responds to an electromagnetic wave. The dielectric function of a material describes the electrical and optical properties versus
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frequency, wavelength, or energy. It describes the polarization (electric polarizability) and absorption properties of the material. Fig 4(d) shows the real 𝜀1(𝜔) and imaginary ε2(ω) part of dielectric function of SrCo2Si2. The static value of dielectric constant is 40.80. The real part 𝜀1(𝜔) goes to below from zero and back to zero up to 46.72 eV. The imaginary part for compound SrCo2Si2 starts from 6.04 and highest peak is 15.84 at 0.72 eV and decrease continuously to zero up to 46.72 eV. The value of 46.72 eV indicating the limit of dielectric function of SrCo2Si2, above this value the material becomes transparent (Russell, 2003).
3.4.5 Conductivity - Conductivity is an optoelectronic event where the conductivity rises due to absorbing of photons. It provides the information about a material will be semiconductor, conductor or insulator. The photo conductivity spectrum of SrCo2Si2 shows in Fig 4(e). From Fig 4(e) it is obvious that the photoconductivity starts with zero photon energy which also ensures the metallic nature of this compound. The photoconductivity of SrCo2Si2 increases due to the absorbing of photons (Sun et al., 2006). From Fig 4(e) we have seen that the photoconductivity spectra have a few maxima and minima peak in the calculated energy range.
3.4.6 Loss function - The photon energy loss spectrum of SrCo2Si2 is shown in Fig 4(f). The energy loss function is a significant matter to reveal the energy loss of a fast electron when it traversed in a material
(Parvin et al., 2015). In loss function graph the peaks related with the plasma resonance and in which associated frequency is called the plasma frequency 𝜔𝑝 (Fox, 2002). The frequency connected to the upper limit of the energy loss spectrum is specified by the
bulk plasma frequency p of the material, which emerges at 2 < 1 and 1 = 0 (Saniz et al., 2006; Al-
meida et al., 2006). The peak in the energy-loss fun-
ction arises when goes through zero from below and 2goes through zero from above. In the energy loss spectra we have seen that the effective plasma frequency of SrCo2Si2 is equal to 14.42 eV. The highest peak is found at about 4.42 eV, which reveal the plasma frequency of SrCo2Si2. The material becomes transparent when the frequency of the incident light is higher than of plasma frequencies mentioned above. Furthermore, the peak in loss function corresponds to the trailing edges in reflection spectra.

4. CONCLUSION: The different physical features such as mechanical, electronic and optical properties of intermetallic SrCo2Si2 have been successively investigated by DFT simulation. The investigated optimized structural parameters are well accord with the available synthesized data. The calculated elastic constants have maintained the born stability criteria which ensure the theoretical mechanical stability of SrCo2Si2. The calculated values of Pugh’s ratio (B/G) and Poisson’s ratio ensure the brittle nature of SrCo2Si2. The stiffer behavior of this phase is ensured by Young’s modulus calculation. The analysis of universal anisotropic factor ensured the anisotropic nature of SrCo2Si2.The calculated band structure shows the metallic nature and major the part arrives from the Sr-4p states at Fermi level. High reflectivity is observed in the ultraviolet region energy site which ensure about the use of SrCo2Si2 as a good coating material at ultraviolet energy region. The absorption quality is good in the ultraviolet region and high refractive index in the infrared region. This result ensured that this compound is promising for absorbing materials in the UV region. The effective plasma frequency of SrCo2Si2 is found to 14.42 eV which ensures that this material becomes transparent when the frequency of the incident photon is higher than 14.42 eV.
5. ACKNOWLEDGEMENT: Thanks to the Physics Department of Pabna University of Science and Technology for giving me opportunity to complete my research work.
6. CONFLICTS OF INTEREST: The authors declared that there is no conflict of interest in this article.
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Citation: Islam MS, Rahman MA, and Farjana N. (2021). The physical properties of ThCr2Si2- type cobased compound SrCo2Si2: an ab-initio study, Int. J. Mat. Math. Sci., 3(3), 50-59. https://doi.org/10.34104/ijmms.021.050059

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