Alloying effect on K to L shell vacancy transfer probabilities in 3d transition metals

Radiation Physics and Chemistry 79 (2010) 1174–1179

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Alloying effect on K to L shell vacancy transfer probabilities in 3d transition metals I. Han a,n, L. Demir b a b

_ ˘ Turkey Faculty of Sciences and Arts, Department of Physics, Ag˘ rı Ibrahim C - ec- en University, TR-04100 Agrı, Faculty of Sciences, Department of Physics, Atat¨ urk University, TR-25240 Erzurum, Turkey

a r t i c l e in f o

a b s t r a c t

Article history: Received 25 May 2010 Accepted 16 July 2010

The alloying effects on K to L shell vacancy transfer probabilities (ZKL) in 3d transition metals have been carried out by X-ray fluorescence studies of various alloy compositions. K X-ray intensity ratios of Ti, Cr, Fe, Co, Ni, and Cu elements in the FexNi1  x, FexCr1  x, NixCr1  x, FexCryNi1  (x + y), TixNi1  x, TixCo1  x, and CoxCu1  x alloys have been measured following excitation by 22.69 keV X-rays from a 10 mCi 109Cd radioactive point source and ZKL values for alloying elements have been determined from these ratios. The spectrum of characteristic K-X-ray photons from samples were detected with a high resolution Si(Li) detector coupled to a 4 K multichannel analyzer. The present investigation makes it possible to perform reliable interpretation of experimental K to L shell vacancy transfer probabilities for various 3d transition metals in alloys and can also provide quantitative information about the changes of K to L shell vacancy transfer probabilities of these metals with alloy composition. & 2010 Elsevier Ltd. All rights reserved.

Keywords: Alloy Alloying effect 3d Transition metal Vacancy transfer probability

1. Introduction X-ray fluorescence (XRF) spectrometry is used world-wide. The most established technique is energy dispersive X-ray fluorescence (EDXRF) for quantitative analysis because EDXRF is relatively inexpensive and requires less technical effort to run the system. EDXRF is very useful for determination of XRF parameters such as production cross sections, fluorescence yields, intensity ratios, and vacancy transfer probabilities. Accurate values of these parameters are required in several fields such as atomic, molecular and radiation physics, material science, environmental science, agriculture, forensic science, dosimetric computations for health physics, cancer therapy, elemental analysis, basic studies of nuclear physics, etc. A vacancy in the inner shell of an atom is produced by various methods; photoionization is one of them. In this method, the incident gamma photon ejects the bound electron to the continuum state, creating a vacancy in the inner shell. This vacancy is filled through radiative or nonradiative processes. In the radiative process, the electron from the higher shell fills the inner shell vacancy, emitting X-ray photons. The number of X-ray photons emitted per vacancy is known as fluorescence yield. In the nonradiative process, instead of an X-ray photon, an electron from a higher shell is emitted and such an electron is known as

n

Corresponding author. Tel./fax: + 90 4722156554. E-mail addresses: [email protected], [email protected] (I. Han). 0969-806X/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2010.07.015

the Auger electron. The number of electrons emitted per vacancy is known as the Auger yield. In these processes, the vacancy in the inner shell (the K shell) is transferred to the higher shells (L, M, etc.). The transfer of the vacancy can also occur within a subshell and such a process is known as the Coster–Kronig transition. The number of L shell vacancies produced per decay of a K shell vacancy is known as the K to L vacancy transfer probability ZKL (Bennal and Badiger, 2006). The K X-ray fluorescence parameters such as intensity ratio and fluorescence yield of 3d transition metals is dependent on the chemical environment of these metals in their alloys (Bhuinya and Padhi, 1993; Raj et al., 2001; Kalayci et al., 2005; Han and Demir, 2009, 2010a, b; Dagistanli et al., 2010) and compounds (Mukoyama et al., 1986; Polasik, 1998; Raj et al., 1998, 2002). The X-ray emission spectra are known to be influenced by the chemical combination and physical properties of X-ray emitting atoms. The variety of physical properties of the 3d transition metals and the large number of applications of these metals and their compounds and alloys cause the need for understanding the X-ray fluorescence parameters such as intensity ratio, fluorescence yields, and vacancy transfer probability of 3d transition metals in various systems. The main aim of present paper is related to investigation of alloying effects on the vacancy transfer probabilities in 3d transition metals alloys. There are a large number of investigations about the vacancy transfer probability ¨ (Rao et al., 1972; Puri et al., 1993; Schonfeld and Janben, 1996, 2000; Ertu˘grul et al., 1997, 2005; Ertu˘grul, 2002; Sharma et al., 2005; Santra et al., 2005; Bonzi, 2006; Han et al., 2007a; Demir and S- ahin, 2007; Tuzluca et al., 2008; Reyes-Herrera and Miranda,

I. Han, L. Demir / Radiation Physics and Chemistry 79 (2010) 1174–1179

1175

¨ gut ¨ et al., 2009; Bennal et al., 2010) but this paper is first 2008; So˘ investigation concerned with alloying effects on ZKL for present alloys with Cd-109 and the measured values of ZKL for Ti, Cr, Fe, Co, Ni, and Cu elements in the FexNi1  x, FexCr1  x, NixCr1  x, FexCryNi1  (x + y), TixNi1  x, TixCo1  x, and CoxCu1  x alloys are being reported here for the first time.

in the sample, difference in the efficiency of the Si(Li) detector and air absorption on the path between the sample and the Si(Li) detector window. The vacancy transfer probabilities from K to L shell (ZKLi ) can be evaluated as the main number of primer Li subshell vacancies produced in the decay of one K shell vacancy through radiative; ZKLi ðRÞ and nonradiative; ZKLi ðAÞ transitions (Rao et al., 1972):

2. Experimental details and data analysis

ZKLi ¼ ZKLi ðRÞ þ ZKLi ðAÞ

The measurements were carried out using high purity alloys (in powder form). The powder material is pelletized into the size of 13 mm diameter. The samples were irradiated using 22.69 keV X-rays from a 10 mCi 109Cd radioactive point source. For each sample, emitted X-rays were detected by a Si(Li) detector (full width at half maximum¼ 160 eV for a 5.9 keV X-ray peak, active area of 12 mm2, thickness of 3 mm, and Be window thickness of 0.025 mm) coupled with a multichannel analyzer system and spectroscopy amplifier. The detector was also placed in a step-down shield made from Pb, Fe, and Al to minimize the detection of any radiation coming directly from the source and scattered from the surroundings. A typical K X-ray spectrum of Fe0.3Cr0.3Ni0.4 alloy is shown in Fig. 1. A careful fitting methodology is required in order to obtain accurate values for the peak areas in the experimental studies. In the present paper, all the X-ray spectra were carefully analyzed by means of the Microcal Origin 7.5 Demo Version software peak fitting program using a multiGaussian least-square fit method in order to determine the accurate peak intensity. Residual plots are also shown in Fig. 1. In the region of the peaks, the residuals are insignificant and the r2 value for the whole range was 0.99 signifying that the peak fitting was satisfactory. To determination of ZKL values, the K X-ray intensity ratios were determined from peak areas fitted to Gaussian function after applying necessary corrections to the data. For measured ratios corrections are needed because of the difference in the Ka and Kb self-attenuations

ZKL ¼

2oK 1þ ðIK b =IK a Þ

where oK is the fluorescence yield of the K shell and IKb/IKa is the intensity ratio of the K X-rays. The average K-shell fluorescence yields, oK, were derived from the measured Ki X-ray fluorescence cross sections using the relationship

oK ¼

sK sK ðEÞ

ð3Þ

where sK ¼ sKa + sKb is the total Ki X-ray fluorescence crosssection and sK(E) is the K-shell photoionization cross-section taken from the tables published by Scofield (1973). The experimental Ki X-ray fluorescence cross sections were evaluated using the relation

sKi ¼

NKi ði ¼ a, bÞ I0 GeKi bt

ð4Þ

where NKi is the net number of counts under the corresponding photopeak, the product I0G is the intensity of the exciting radiation falling on the area of the target samples visible to the

Corr Coef = 0.99978

FexCry Ni1-x x = 0.3; y = 0.3

Fe K β

30000 25000 20000 15000

5000

Fe K α

Cr K β

10000

Ni K β

Cr K α

Counts per channel

ð2Þ

Ni K α

35000

ð1Þ

The experimental K to L shell total vacancy transfer probabilities, ZKL, were obtained by using following equation (Schonfeld and Janben, 1996):

0 600

800

1000

1200

1400

Residual

Channel number 500 0 -500

600

800

1000

1200

Fig. 1. A typical K X-ray spectrum of Fe0.3Cr0.3Ni0.4 alloy excited with 22.69 keV X-rays from

1400 109

Cd radioactive point source.

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I. Han, L. Demir / Radiation Physics and Chemistry 79 (2010) 1174–1179

target for both the incident and emitted photons, and eKa and eKb are the detector-efficiency values for the Ka and Kb X-rays, respectively.

4.08

log (I0Gε)

4.04

3. Results and discussion

4.00 3.96 3

2

log(I0Gε) = A0/E + A1/E + A2/E + A3 2

3.92

r = 0.94505 A0 = 3.74655 ± 0.45629 A1 = -0.02442 ± 0.19612

3.88

A2 = 0.01561 ± 0.02702 A3 = -0.00103 ± 0.00119

3.84 5

4

6

8 7 Energy (keV)

9

10

11

Fig. 2. Plot of the factor I0Ge as a function of weighted mean K X-ray energy.

detector, eKi , is the detector efficiency for Ki X-rays, t is the areal mass of the sample in g/cm2, and b is the self-absorption correction factor for the incident photons and emitted K X-ray photons. b was calculated using the relation     1exp  ðm=rÞi =cos y1 þ ðm=rÞe =cos y2 t   ð5Þ b¼ ðm=rÞi =cos y1 þ ðm=rÞe =cos y2 t where (m/r)i and (m/r)e are the mass attenuation coefficients (cm2/g) of incident photons and emitted characteristic X-rays, respectively. y1 and y2 are the angles of incident photons and emitted X-rays with respect to the normal at the surface of the sample in the present setup and t is the mass thickness of the sample in g/cm2. To estimate the self-absorption correction in the sample and the absorption correction in the air path we used the mass attenuation coefficients obtained by means of a computer program named WINXCOM (Gerward et al., 2001, 2004) which is based on the DOS-based compilation of XCOM developed by Berger and Hubbell (1987, 1999) for calculating mass attenuation coefficients or photon interaction cross-section for any element, compound, or mixture at energies 1 keV to 100 GeV. This program uses mixture rule to calculate the partial and total mass attenuation coefficients for all elements, compounds, and mixtures at standard as well as selected energies. The mass attenuation coefficients (m/r)C for any chemical compound or mixture are estimated using the elemental values in the following Bragg’s-rule formula (Jackson and Hawkes, 1981): X ðm=rÞC ¼ wi ðm=rÞi ð6Þ i

Table 1 ZKL values for Fe and Ni in pure metals and FexNi1  x alloys. Sample

Fe Fe0.8Ni0.2 Fe0.7Ni0.3 Fe0.6Ni0.4 Fe0.5Ni0.5 Fe0.4Ni0.6 Fe0.3Ni0.7 Fe0.2Ni0.8 Ni a b

ð6Þ

where NKa and NKb represent the counts under the Ka and Kb peaks, bKa and bKb are the self-absorption correction factors of the

Experimental

Theoretical

Fe

Ni

1.436 1.510 1.524 1.543 1.566 1.601 1.614 1.651 –

– 1.674 1.631 1.585 1.537 1.495 1.476 1.452 1.388

1.439a – – – – – – – 1.375a

1.447b – – – – – – – 1.388b

Rao et al. (1972). ¨ Schonfeld and Janben (2000).

Table 2 ZKL values for Fe and Cr in pure metals and FexCr1  x alloys. Sample

Experimental Fe

Fe Fe0.9Cr0.1 Fe0.7Cr0.3 Fe0.5Cr0.5 Cr a

where wi is the proportion by weight of the ith constituent and (m/r)i is the mass attenuation coefficient for the ith constituent in the compound. In this study, the effective incident photon flux I0GeKi, which contains terms related to the incident photon flux, geometrical factor, and the efficiency of the X-ray detector, was determined by measuring t, b, and the K X-ray intensities from different thin samples and using theoretical sKi values in Eq. (4). The measured I0Ge values for the present geometry were plotted as a function of the mean K X-ray energy in Fig. 2. The IKb/IKa intensity ratio is obtained from the following equation (Han et al., 2007b): IK b NK b bK a eK a ¼ IK a NK a bK b eK b

K to L shell vacancy transfer probabilities (ZKL) for 3d transition elements in pure metals and their different alloy compositions (for FexNi1  x, x¼ 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and 0.2; for FexCr1  x, x¼0.9, 0.7, and 0.5; for NixCr1  x, x¼0.8, 0.6, 0.5, 0.4, and 0.2; for FexCryNi1  (x + y), x ¼0.7, y¼0.1, x¼0.5, y¼0.2, x ¼0.4, y¼ 0.3, x¼0.3, y¼0.3, x¼0.2, y¼0.2, and x ¼0.1, y¼0.2; for TixNi1  x, x¼0.7, 0.6, 0.5, 0.4, and 0.3; for TixCo1  x, x ¼0.7, 0.6, 0.5, 0.4, and 0.3; for CoxCu1  x, x ¼0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and 0.2) were measured. The ZKL measured for the present samples have been tabulated in Tables 1–7. The total experimental uncertainty in the measured ZKL values is estimated to be 3–7%. This uncertainty

b

1.436 1.507 1.520 1.564

Theoretical Cr

1.704 1.663 1.640 1.410

1.439a – – – 1.495a

1.447b – – – 1.508b

Rao et al. (1972). ¨ Schonfeld and Janben (2000).

Table 3 ZKL values for Ni and Cr in pure and NixCr1  x alloys. Sample

Experimental Ni

Ni Ni0.8Cr0.2 Ni0.6Cr0.4 Ni0.5Cr0.5 Ni0.4Cr0.6 Ni0.2Cr0.8 Cr a b

1.388 1.330 1.379 1.427 1.488 1.532

Rao et al. (1972). ¨ Schonfeld and Janben (2000).

Theoretical Cr

1.710 1.662 1.632 1.576 1.543 1.410

1.375a – – – – – 1.495a

1.388b – – – – – 1.508b

I. Han, L. Demir / Radiation Physics and Chemistry 79 (2010) 1174–1179

Table 4 ZKL values for Fe, Cr and Ni in pure metals and FexCryNi1  (x + y) alloys.

a b c

Fe

Cr

Ni

1.436 – – 1.419 1.468 1.477 1.533 1.611 1.686

– 1.410 – 1.744 1.717 1.686 1.691 1.711 1.713

– – 1.388 1.653 1.595 1.590 1.512 1.438 1.372

Theoretical

Other exp.

1.439a 1.495a 1.375a – – – – – –

1.442 70.144c 1.538 70.123c 1.364 70.123c – – – – – –

1.447b 1.508b 1.388b – – – – – –

Rao et al. (1972). ¨ Schonfeld and Janben (2000). ¨ gut ¨ et al. (2009). So˘

Table 5 ZKL values for Ti and Ni in pure metals and TixNi1  x alloys. Sample

Experimental

Theoretical

Ti Ti Ti0.7Ni0.3 Ti0.6Ni0.4 Ti0.5Ni0.5 Ti0.4Ni0.6 Ti0.3Ni0.7 Ni a b

Ni a

1.568 1.568 1.599 1.615 1.622 1.664

1.679 1.599 1.583 1.491 1.479 1.388

b

1.566 – – – – – 1.388b

1.548 – – – – – 1.375a

Rao et al. (1972). ¨ Schonfeld and Janben (2000).

Table 6 ZKL values for Ti and Co in pure metals and TixCo1  x alloys. Sample

Experimental Ti

Ti Ti0.7Co0.3 Ti0.6Co0.4 Ti0.5Co0.5 Ti0.4Co0.6 Ti0.3Co0.7 Co a b

1.568 1.616 1.631 1.629 1.621 1.679

Theoretical/Other exp. Co

1.650 1.623 1.575 1.579 1.482 1.384

Co Co Co0.8Cu0.2 Co0.7Cu0.3 Co0.6Cu0.4 Co0.5Cu0.5 Co0.4Cu0.6 Co0.3Cu0.7 Co0.2Cu0.8 Cu a b

1.384 1.481 1.498 1.515 1.560 1.586 1.621 1.656

1.566 – – – – – 1.418a

1.586 7 0.127 – – – – – 1.420 7 0.142b

¨ Schonfeld and Janben (2000). ¨ gut ¨ et al. (2009). So˘

Theoretical/Other exp. Cu

1.672 1.623 1.565 1.527 1.484 1.447 1.397 1.387

Fe in FexNi1-x Ni in FexNi1-x

1.7

1.6

1.5

1.4

1.3

1.418a – – – – – – – 1.357a

0.4

1.420 7 0.142b – – – – – – – 1.342 7 0.121b

0.6

0.8

1.0

own metal concentration

b

Table 7 ZKL values for Co and Cu in pure metals and CoxCu1  x alloys. Experimental

1.8

0.2 a

¨ Schonfeld and Janben (2000). ¨ gut ¨ et al. (2009). So˘

Sample

K to L shell vacancy transfer probabilities (KL)

Fe Cr Ni Fe0.7Cr0.1Ni0.2 Fe0.5Cr0.2Ni0.3 Fe0.4Cr0.3Ni0.3 Fe0.3Cr0.3Ni0.4 Fe0.2Cr0.2Ni0.6 Fe0.1Cr0.2Ni0.7

Experimental

arises from the uncertainties in various parameters used to the determination of the ZKL values including errors due to the evaluation of peak area, detector efficiency, self-absorption factors, and target thickness measurements. The ZKL values obtained for pure Ti, Fe, Cr, Ni, Cu, and Co metals (Tables 1–7) are compatible with the results of Rao et al. (1972), ¨ ¨ gut ¨ et al. (2009). In this study, Schonfeld and Janben (2000), and So˘ the ZKL values of Ti, Cr, Fe, Cu, Ni, and Co in different composition alloys were performed using the K X-ray intensity ratios and K shell fluorescence yields. The present agreement between experimental results and the theoretical and other experimental values shows that using these parameters for determination of ZKL is very useful. Figs. 3–5 is drawn for graphical presentation of values in Tables 1–7 and shows change of ZKL values as a function of their own concentrations in FexNi1  x, FexCryNi1  (x + y) and CoxCu1  x, alloys, respectively. It can be seen from these tables and figures that for both binary and ternary alloys, changes of ZKL values with element concentration in alloy are similar. As seen in Tables 1–7, the ZKL values for 3d metals in alloys are significantly different from that of the pure metal. This deviation is related to the electron rearrangement between 3d and 4s, 4p

Fig. 3. The change of K to L shell vacancy transfer probabilities (ZKL) for Fe and Ni as a function of their own concentrations in FexNi1  x alloys.

K to L shell vacancy transfer probabilities(KL)

Sample

1177

1.8 Fe in FexCryNi1-(x+y) Cr in FexCryNi1-(x+y) Ni in FexCryNi1-(x+y)

1.6

1.4

1.2 0.0

0.2

0.4

0.6

0.8

1.0

own metal concentration Fig. 4. The change of K to L shell vacancy transfer probabilities (ZKL) for Fe and Ni as a function of their own concentrations in FexCryNi1  (x + y) alloys (own metal concentration refers to x for Fe, y for Cr and 1  (x + y) for Ni).

K to L shell vacancy transfer probabilities (KL)

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I. Han, L. Demir / Radiation Physics and Chemistry 79 (2010) 1174–1179

1.8 Co in CoxCu1-x Cu in CoxCu1-x

1.7

1.6

1.5

1.4

1.3 0.2

0.4

0.6

0.8

1.0

own metal concentration Fig. 5. The change of K to L shell vacancy transfer probabilities (ZKL) for Co and Cu as a function of their own concentrations in CoxCu1  x alloys.

valence shells (delocalization) and/or charge transfer of 3d electrons from one element to another. The delocalization and charge transfer phenomena can be in opposite directions and larger than the others; therefore, the valance electronic arrangement for these alloys are different. This can cause some uneven change in relation between the ZKL values and the own metal concentration of 3d transition elements in alloys. Electrons removed from the 3d state of one element influence screening effect on the 3d and 4s electrons and binding energies of 3d and 4s electrons. Changing the screening effect and binding energies of 3d and 4s electrons causes a change in the ZKL values of metal atoms. The number of transferred electrons from the 3d state of one element to the 3d state of other element is different for different composition, so the ZKL values of metals depend on alloy compositions. The alloying effect is clearly observed in the K to L vacancy transfer probabilities. The changes in the ZKL with alloy compositions are in same directions for both elements in a certain alloy and generally, there is a decrease in ZKL values of metals with increasing concentration in alloys. The origin of change in K to L vacancy transfer probabilities of 3d transition metals should be interpreted in terms of the change in the electronic configuration of alloying metals. The 3d transition metal alloys plays an important role in fundamental and applied research due to variety of physical properties. The physical properties of binary and ternary 3d transition metal alloys depend strongly on the valence electronic structure, which is responsible for the observed change in ZKL values of the Ti, Fe, Cr, Ni, Cu, and Co in different alloys. Experimental results obtained in this investigation show that ZKL values for alloys exhibit a great dependence on alloy composition. The ZKL values for 3d transition metals are modified with alloying of these metals, therefore ZKL are sensitive tools to investigate alloying effect. Thus, the specific alloy composition may be important in developing different special properties or to improve the present characteristics of 3d transition metal alloys. The knowledge of alloying effect on K to L shell vacancy transfer probabilities is important for determining the different and special features of the 3d transition metal alloys.

4. Conclusion Present study has been performed in exploring the alloying effect on the K to L vacancy transfer probabilities (ZKL) of 3d transition metals. For this reason ZKL values were measured for

pure 3d metals and their different alloy compositions. The results indicate that alloying effect cause significant changes in ZKL values in 3d transition metal alloys, in other words K to L vacancy transfer probabilities is affected by the alloying operation. This arises from change of valence electron structure with delocalization and/or charge transfer in alloys. This means that physical properties of the alloy are strongly influenced by the alloy composition. Electrical, magnetic, and other properties of 3d transition metal alloys can be enhanced and controlled with certain chemical composition. Consequently, private alloy composition may enable the production of alloys with ideal physical properties for specific applications. To attain more definite results and to satisfy conclusions about alloying effects on K to L vacancy transfer probabilities, studies should be continued for different 3d transition metal alloys.

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