Kα intensity ratios for Fe, Se, Te, FeSe, FeTe and TeSe

Radiation Physics and Chemistry 81 (2012) 1837–1841

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Determination of K shell fluorescence cross-section and Kb/Ka intensity ratios for Fe, Se, Te, FeSe, FeTe and TeSe M. Saydam a,n, C. Aksoy a, E. Cengiz a, C. Alas-alvar b, E. Tıras-o˘glu a, G. Apaydın a a b

Department of Physics, Faculty of Science, Karadeniz Technical University, Kalkınma street, 61080 Trabzon, Turkey Department of Physics, Faculty of Arts and Science, Giresun University, 28000 Giresun, Turkey

H I G H L I G H T S c c c

TeSe, FeSe and FeTe complexes have affected each other in terms of charge transfer. Fe excitement and enhancement have been made by Se and Te. Attractive interactions between electrons can help to becoming superconductivity.

a r t i c l e i n f o

abstract

Article history: Received 10 January 2012 Accepted 12 August 2012 Available online 21 August 2012

The fluorescence cross-sections (sKi) and the intensity ratios Kb/Ka for pure Fe, Se, Te elements and FeSe, FeTe, TeSe complexes have been investigated. The samples were excited by 59.5 keV g-rays from 241Am annular radioactive source and emitted X-rays. They were counted by an Ultra-LEGe detector with resolution of 150 eV at 5.9 keV. For pure elements results have been compared with the theoretical calculated values. According to our results band length and mutual interaction of atoms affected the results. We claimed that these effects would help researchers who study on superconductors, especially determining which compound can be show the superconductor properties. & 2012 Elsevier Ltd. All rights reserved.

Keywords: K-shell Superconductors Cross-sections Intensity ratios

1. Introduction The accurate values of the X-ray fluorescence cross-sections (sKa and sKb) and intensity ratios (Kb/Ka) are important as they have been used in atomic, molecular, radiation, materials health physics and elemental analysis, using Energy Dispersive X-ray fluorescence (EDXRF). There are many studies on the fluorescence cross-sections sKi (i¼ a,b) and the intensity ratios Kb/Ka for some pure elements. At 59.5 and 123.6 keV, the intensity ratios Kb/Ka have been theoretically and experimentally determined by Cevik et al. (2007). Durak and ¨ zdemir (2001) explained that the sKi (i¼ a,b) and yields of 14 O elements in the atomic range 25rZr47 using the photo-ionization. Han et al. (2007) has measured the K X-ray parameters for some elements in the atomic range 22rZr68. Rao et al. (1986) explained that Kb/Ka depend on the excitation modes in 3d elements. Kb/Ka in atomic range 22rZr 69 at 59.5 keV have been measured by Ertu˘grul et al. (2001). Ertugrul and Simsek (2002) researched K X-ray relative intensity for some high Z elements. The Kb/Ka intensity ratios for 3d elements change with changing crystal structure (Dagıstanlı and Mutlu, 2012). Singh (2009) investigated the electronic,

band, and crystal structure of iron-based superconductor. He found that Fe–Fe interaction is very important for FeSe compounds. In this study, the sKa and sKb and Kb/Ka have been investigated. The measured results can show how the elements affect each other in terms of electron interactions. We claimed that the electron interactions can help to researcher in first step while determining materials which could be superconducting after the required process in terms of atomic structure.

2. Experimental procedure 2.1. Sample preparation Pure elements which commercially obtained Fe (% 99.999), Se(% 99.999), and Te(% 99.999) were taken from Sigma Aldrich. TeSe, FeSe and FeTe complexes were prepared and mixed in stoichiometry (0.5; 0.5).The samples were pressed by using Perkinelmer Press to obtain samples different weight and different thickness in 13 mm. 2.2. Experimental method

n

Corresponding author. Tel.: þ90 462 3772507; fax: þ90 462 3253195. E-mail address: [email protected] (M. Saydam).

0969-806X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2012.08.003

The geometry of the experimental set-up for an annular source can be seen in Fig. 1. included an Ultra-LEGe (ultra low energy

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Mylar Sample 241 Am annular source

Fiber

Berilium Window

Pb annular collimator

UltaLEGe Dedector

Holder

Fig. 1. Geometry of the experimental setup.

Table 1 Comparison of present experimental, theoretical and other experimental results for sKa and sKb.

sKa (b/atom)

sKb (b/atom)

Sample

Experimental

Puri et al. (1995)

Cevik et al. (2007)

Theoretical

Experimental

Puri et al. (1995)

Cevik et al. (2007)

Theoretical

Fe Se Te FeSea FeSeb FeTea FeTec TeSeb TeSec

27.7377 0.26 134.0547 0.68 924.2187 4.34 24.3497 0.33 137.6677 0.80 22.017 7 0.37 940.520 7 5.31 125.7677 0.82 935.7077 5.45

25.74 122.96 880.71 – – – – – –

28.98 70.34 146.5370.73 1042.9875.16 – – – – – –

26.433 130.699 890.841 – – – – – –

3.7007 0.16 22.053 7 0.25 196.2607 0.95 3.427 7 0.22 22.6367 0.32 3.369 7 0.27 202.3887 1.56 20.297 7 0.42 199.8957 1.74

3.58 19.98 202.55 – – – – – –

3.68 7 0.13 22.08 7 0.29 218.417 1.93 – – – – – –

3.618 20.892 189.988 – – – – – –

a b c

For Fe. For Se. For Te.

Table 2 Comparison of present experimental, theoretical and other experimental results for Kb/Ka. Theoretical values Sample

Fe Se Te FeSea FeSeb FeTea FeTec TeSeb TeSec a b c

Experimental

0.1334 7 0.007 0.1645 7 0.009 0.2123 7 0.011 0.1407 7 0.008 0.1644 7 0.009 0.1530 7 0.008 0.2149 7 0.011 0.1614 7 0.008 0.2136 7 0.011

Experimental values Scofield (1974a) 0.1391 0.1624 – – – – – – –

Scofield (1974b) 0.1208 0.1425 0.2132 – – – – – –

Manson and Kennedy (1974) 0.1203 0.1416 0.2119 – – – – – –

Salem et al. (1974) 0.135 0.157 0.225 – – – – – –

Ertu˘grul et al. Cevik et al. (2007) (2001) 0.133 0.157 0.230 – – – – – –

Hansen et al. (1970)

0.1357 0.007 0.1677 0.006 0.2267 0.009 – – – – – –

0.128 0.151 0.230 – – – – – –

Khan and Karimi (1980) 0.134 0.161 0.227 – – – – – –

Ertu˘gral et al. (2007) 0.1324 70.005 0.1612 70.005 0.2194 70.008 – – – – – –

For Fe. For Se. For Te.

Ge detector; FWHM 150 eV at 5.9 keV, active area 13 mm2, thickness 5 mm and Be window thickness 30 mm). The out preamplifier, with a pulse pile-up rejection capability, was fed to a multi-channel analyzer interfaced with a private computer provided with suitable software for data acquisition and peak analysis. In this experimental set-up, 59.5 keV photons emitted by an annular 50 mCi Am-241 radioactive sources were utilized. The experimental K shell X-ray intensity ratios Kb/Ka were calculated the following equation: IK b N K b bK a e K b ¼ IK a N K a bK b e K a

ð1Þ

where NKb and NKa represent the net count under Kb and Ka peaks, bKa and bKb are the self-absorption correction factors of the target. eKb and eKa are the detector efficiencies for Kb and Ka X-rays. The sKi were evacuated by using the following equation:

sKi ¼

N Ki , I0 GeKi bKi t i

ði ¼ a, bÞ

ð2Þ

where NKi and bKi (i¼ a,b) have the same meaning as Eq.(1), I0 is the intensity of exciting radiation, G is the geometric factor, ti is the thickness of the target (g cm  2).

M. Saydam et al. / Radiation Physics and Chemistry 81 (2012) 1837–1841

The self-absorption correction factor bKi was calculated using the equation:

bKi ¼

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The term sKi represents the K X-ray fluorescence crosssections and is given by:

sKi ¼ sKP oK f Ki ði ¼ a, bÞ

1exp½ðminc =cosy1 þ memt cosy2 Þt i  ðminc =cosy1 þ memt =cosy2 Þt i

ð3Þ

where minc and memt are the total mass absorption coefficients (cm2/g) of incident photons and the emitted characteristic X-rays (Hubbell, 1999). The angles of incident and emitted photons X-rays with respect to the normal at the surface of samples y1 and y2 were equal to 451 and 901 in the present experimental set-up, respectively.

ð4Þ

where sKP is the K shell photoionization cross-section (Scofield, 1973), oK is the fluorescence yield (Krause, 1979) and fKi is fractional X-ray emission rate fKa taken from Broll0 s (1986) and fKb calculated from the equation: f K b ¼ 1f K a

ð5Þ

3. Result and discussion Kα

The sKi (i ¼ a,b) and Kb/Ka were investigated for pure Fe, Se, Te and their complexes FeSe, FeTe and TeSe. The results are listed in Table 1 and Table 2. According to Table 1, the values of the sKi (i ¼ a,b) for pure elements are accordance with the theoretical and the other experimental values. The comparison values have been indicated in Fig. 4. Especially, Fe fluorescence cross-section values decreased in the FeSe, FeTe compounds. It means that Fe atom takes an electron from Se and Te. Since Se and Te elements have different K shell energies and these energies are much bigger than Fe, K shell energy of Fe atoms have been enhanced by Se and Te

Count

1.2x105

8.0x104

4.0x104

Kβ

0.0 6x102

0.24

7x102

8x102 Channel

9x102 0.22

Se Kα 0.20 Intensity ratios

Count

4.0x104

2.0x104

present Scoffield 1974 Manson 1974 Salem et al. 1974 Ertugrul et al. 2001 Çevik et al. 2007 Hansen et al. 1970 Khan 1980 Ertugral et al. 2007

0.18 0.16 0.14

Fe Kα

Se Kβ 0.12

Fe Kβ

Fe

0.0 6.0x102 Channel

9.0x102 Te Kα

6.0x105

Count

4.0x105

Te Kβ12

2.0x105 Se Kα Se Kβ

Escape Peaks

0.0 5.0x102

1.0x103

1.5x103 Channel

2.0x103

Fig. 2. (a) Typical Ka and Kb photopeak for pure Se element. (b) Typical K-X-rays spectra for FeSe complex. (c) Typical K-X-rays spectra for Te–Se complex.

Te

Fig. 3. Comparison with the theoretical and the experimental values for intensity ratios.

Total photoionization cross-sections values

3.0x102

Se

1200

FFAST (Chantler et al. 1995-2000) Puri et al. 1995 Theoretical value Experimentalvalue Çevik et al. 2007

800

400

0 Fe

Se

Te

Fig. 4. Comparison with the experimental and the theoretical values which are calculated from Eq. (4) for total photoionization cross-sections at the 59.5 keV (Puri et al., 1995, FFAST (Chantler et al., 1995, 2000), Cevik et al., (2007))).

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atoms, and so avalanche have become in the complexes. Se, FeSe and TeSe K-X-rays peaks have been shown in Fig. 2(a–c). It is well known that sKb and Kb/Ka rise with increasing atomic number. As seen in Table 2, Kb to Ka intensity ratios increase with increasing atomic number. Elements have different ionic size because of that, chemical substitution on Fe site and Se site have been observed different properties. Te has much bigger ionic size than Se and Fe. Bond length of Fe–Se, Fe–Te (Lehman et al., 2009) and Se–Te are 2.39 A1, 2.55 A1 and 2.54 A1, respectively. And so, the bond length of Fe–Se and Fe–Te are smaller than Se–Te. Therefore, binding energy of FeSe and FeTe complexes bigger than SeTe complex. It means that mutual interactions on the Fe–Se and Fe–Te are quite robust. The bond length of Se–Te

complex have been found that using the Gauss View 4.1 software and this software shapes of complexes have been shown in Fig. 5 (Frisch et al., 2003). Environmental factors, such as electronegativitiy, oxidation numbers etc., affect the compounds, complexes and alloys. Chemical effects on K and L shell production cross-sections and tranfer probabilities in Nb compounds were investigated by Cengiz et al. (2008) and sKa cross-section is small because of the chemical effect. Charge transfer effects were explained that Zn complexes and sKi (i¼ a, b) are affected by interaction between the central atom and ligand atoms, so, chemical environmental factors influence the measurements (Aylıkcı et al., 2009). Alloying effect on the K shell fluorescence yield (oK) in CrxNi1  x and CrxAl1  x alloys was determined. In the CrxNi1  x alloy the oK of chromium decreases with decreasing nickel concentration. On the other hand, in the CrxAl1  x alloy the oK of chromium increases with decrease in aluminium concentration. These differences in electronegativity, charge transition, may occur changing the binding energies. In these alloys, electrons which are in the outermost shell, interact with neighbouring ions electrostatically. This effect may change the binding energies of the outermost electrons, Auger transition probability and oK. ¨ ukkasap, ¨ (Buy 1998). In the present paper, measurements have been compared with the theoretical values and the other experimental values. These values have been indicated in Figs. 3 and 4. According to the Figs. 3 and 4, our measurements are appropriate to the other values. Because of counting statistic, background determination, target thickness, absorption correction factor, and detector efficiency, evaluation of the peak area errors have observed some differences between our measurements and the other values. The errors present measurements are approximately 6% due to the counting statistics, background determination; self absorption correction and the detector efficiency QUOTE I0Ge determination. This error is the quadrature sum of the uncertainties in the different parameters used to evaluate the K shell fluorescence parameters, i.e. target thickness (r2%), the evaluation of the peak area (r3%), the detector efficiency I0GeKi ( r3%) and the absorption correction factor ( r3%).Fig. 5 In this study, our measurements explain that excitement, and changing of the crystal structure of the elements arise from the mutual interaction between the electrons. Very useful results obtained from current study may be the first step before preparing materials thought to be superconducting.

Acknowledgement We would like to thank Mrs. Meltem Saydam for her contributions to science as the other authors. Unfortunately, she passed away four days later when this manuscript accepted. We will always remember her. References

Fig. 5. Shapes of complexes (Frisch et al., 2003) and their bond lengths are (FeSe, FeTe. and SeTe) are 2.39 A1, 2.55 A1 and 2.54 A1 respectively. Angles of FeSe and FeTe are 104.021 and 94.091 (Lehman et al., 2009).

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