Enhancing the physical, optical and shielding properties for ternary Sb2O3–B2O3–K2O glasses

Ternary Sb2O3–B2O3–K2O glass system, with general composition of x Sb2O3–(70-x) B2O3–30 K2O (where x = 0, 10, 20, 30, 40, 50) were prepared using melt-quenching technique. Structures of these glasses were investigated using XRD analysis and FT-IR spectroscopy. The optical properties were investigated using the UV–Vis NIR JASCO (Model V-670) Double Beam Spectrophotometer. Different physical parameters, such as density (ρ), molar volume (VM), oxygen molar volume (VO) and oxygen packing density values (OPD) have been estimated. Also, the Gamma radiation shielding ability have been characterized for the investigated glasses using Phy-X/PSD software in the photon energy range (0.015–15 MeV). XRD analysis confirm the amorphous nature of the prepared glasses. The optical energy gap of SBK glasses is decreasing from 4 to 2.63 eV with increasing Sb2O3 content while refractive index is increasing from 2.17 to 2.5 because of increasing the non-bridging oxygens (NBOs) in the glass matrix. The molar refractivity (Rm), molar polarizability (αm) and the third-order nonlinear optical susceptibility values χ3 have been calculated, their values are found to increase with increasing Sb2O3 content. Glass density and molar volume values for the SBK glasses increase with increasing Sb2O3 content. Increasing the Sb2O3 concentration enhance the radiation shielding features of the prepared glasses against gamma rays and neutrons. Hence, the mass attenuation coefficient (MAC) increases from 8.6 to 35.4 cm2/gm while the half value layer (HVL) decreases from 0.036 to 0.0046 cm at 0.015 MeV as the Sb2O3 concentration increases from 0 to 50 mol%. The fast neutron cross section of the six investigated SBK glasses are (0.087, 0.092, 0.095, 0.091, 0.094 and 0.092 cm−1), respectively.


Introduction
Conventional glass formers such as phosphorus, silicon, boron, or germanium oxides is required and important in determining common oxide glass properties [1]. Heavy metal oxide glasses containing antimony, telluride, bismuth, tungsten, or lead have gained great interest and have preferred over the conventional glass because of their different advantages. They have high refractive index, low phonon energy, high thermal expansion and extended optical transmission spectrum [2][3][4][5][6]. Their attractive properties make them suitable candidate in many applications as optical amplifiers and non-linear optics components [2][3][4][5][6].
Antimony oxide-based glasses are considered one member of heavy metal oxide glasses family that was predicted by Zachariasen and confirmed by many authors [7][8][9][10]. These glasses gained significant interest in various technological applications as, nonlinear optical devices such as power limiters and ultra-fast optical switches [11,12]. Pure Sb 2 O 3 glasses was found to be a weak glass former and chemically unstable [13]. So, to enhance the vitrification behavior and to provide stabilization to the Sb 2 O 3 network, it was preferable to incorporate the Sb 2 O 3 with other conventional glass formers such as, SiO 2 [14], B 2 O 3 [15], P 2 O 5 [16,17]. Antimony borate glasses have gained considerable interest because they can be applicable in the field of optics and electronics as a result of the heavy cations polarizability and the stereochemically alien lone pair of electrons present in the case of Sb 3? [18].
An important benefit of heavy metal oxide glasses (HMO) is to be used as shielding material against gamma-ray, x-ray and neutrons because of the high atomic number and density of heavy metals [19][20][21][22][23][24]. It was found that Sb 2 O 3 improve the radiation attenuation properties of tellurite glasses containing V 2 O 5 and Nb 2 O 5 (TSVN) [19]. A.S. Abouhaswa et al. prove that Bi 2 O 3 -B 2 O 3 -Sb 2 O 3 -Li 2 O glasses (BSLBglasses) have a higher photon protection capacity than ordinary (OC) and barite (BC) concretes [20]. Also it was found that MoO 3 improve the produced glass network compactness of alumino lead borate glasses and enhance the glass protection against neutrons [21]. G.A. Alharshan et al. studied the radiation-transmission and self-absorption factors of P 2 O 5 -SrO -Sb 2 O 3 glass system (PSS glass) [22], they found that some of PSS glasses are better than both RS-253-G18 (standard commercial shield) and ordinary concrete in radiations shielding. K.C. Sekhar et al. investigated the effect of PbO on Bi 2 O 3 -B 2 O 3 -Fe 2 O 3 glasses, they showed that their system is applicable for advanced optical and radiation shielding applications [23]. M. S. Al-Buriahi et al. studied the effect of heavy metal oxides (SrO, Al 2 O 3 , CdO, ZnO, PbO and Bi 2 O 3 ) on (TeO 2 -B 2 O 3 -BaO-Er 2 O 3 ) glasses, they found that these glasses are desirable shielding materials against gamma ray and neutrons [24].
In this work, ternary Sb 2 O 3 -B 2 O 3 -K 2 O glass system was prepared and investigated. B 2 O 3 was chosen as a good network former because it possesses high bond strength and low cation size. The addition of Alkali oxide (K 2 O) modifies the glass network and transform tetrahedral (BO 4 ) units to trigonal (BO 3 ) units by the non-bridging oxygens formation [25]. Sb 2 O 3 is added to standard glass formers to improve vitrification behavior, but it also raises phonon energy, which reduces infrared transmission [5,6]. The current study's goal is to explore the Sb 2 O 3 -B 2 O 3 -K 2 O glass. Since Sb has a larger atomic radius and density than B, this glass should have a higher refractive index, making it more appropriate for nonlinear optical applications. Additionally, Sb 2 O 3 incorporation is anticipated to improve radiation shielding applications due to higher atomic weight and atomic number of Antimony compared to Boron. The glasses under investigation are with a general composition of (mol%) x Sb 2 O 3 -(70-x) B 2 O 3 -30 K 2 O (where x = 0, 10,20,30,40,50). The Sb 2 O 3 -B 2 O 3 -K 2 O glasses structure was investigated using XRD analysis and FT-IR spectroscopy. The optical properties were investigated using the UV-Vis-NIR JASCO (Model V-670) Double Beam spectrophotometer. The important parameters, such as density (q), molar volume (V M ), oxygen molar volume (V O ) and oxygen packing density values (OPD) have been estimated. Also, the Gamma radiation shielding ability have been characterized for the Sb 2 O 3 -B 2 O 3 -K 2 O glasses using Phy-X/PSD software.

SBK glass characterizations
The XRD investigation was performed to emphasize the amorphous nature of the investigated glass samples. The XRD data for the powder glass samples was identified by X-ray diffractometer (D8 Discovery Bruker Company) at condition of 40 kV and 40AM (1600 W) at speed scan 0.01 P in the 2h range from 10°t o 808, and with the aid of automated computer system. FT-IR spectroscopy analysis (type JASCO 430) was used to study the structure changes of investigated glass samples at room temperature and at spectral range 400-4000 cm -1 . The optical properties of the SBK glasses were investigated using the UV-Vis-NIR JASCO (Model V-670) Double Beam Spectrophotometer. A good polished SBK glass pellets of thickness 3 mm approximately was used. The spectra of the investigated glass were recorded at wavelength range 200-2500 nm. The Gamma radiation shielding ability have been characterized for the Sb 2 O 3 -B 2 O 3 -K 2 O glasses using Phy-X/PSD software.

XRD structural studies for SBK glasses
The XRD analysis was performed for the SBK glass samples to examine the glass nature. The XRD data patterns for the SBK glass samples are shown in   [13,[26][27][28][29][30][31]. The average crystallite size was evaluated from Debye-Scherrer's equation as following [32]: where D is the average crystalline size, h is the diffraction angle, b is the peak width at half maximum height intensity, k is the wavelength of the incident x-ray and K is the so-called Scherrer constant. K relies on the size distribution, shape, and indices of the diffraction line as well as the definition of b, whether it be FWHM or integral width [33]. K can have values anywhere from 0.62 and 2.08. In this paper, K = 0.99 was used. The average crystal size formed in SBK6 sample was found about 25 nm. Debye-Scherrer's equation showed a good accuracy in determination the crystallite size smaller than 100 nm as compared with other methods (Williamson-Hall method and the Rietveld refinement) [34], also in comparison with other techniques as transmission (TEM) and scanning electron microscopes (SEM) showed a good accuracy in estimating the small crystallite size less than 50-60 nm [34].

FT-IR analysis for SBK glasses
The structural properties of the SBK glasses were investigated by The Fourier transform IR (FT-IR) spectroscopy. The FT-IR spectra of SBK glasses in the spectral rang 400-4000 cm -1 is shown in Fig. 4. Figure 5 shows the FT-IR spectrum and the deconvolution of the FT-IR spectra of the SBK glasses. The deconvolution parameters and the band nature are presented in Table 2 [35,36]. The band around 3000-3900 cm -1 is attributed to the hydroxyl groups, which indicates the presence of amount of water.

Optical properties of SBK glasses
The optical properties of the SBK glasses were investigated using the UV-Vis NIR JASCO (Model V-670) Double Beam spectrophotometer. The UV-vis absorbance spectra for the SBK glasses are shown in Fig. 6 (a). As shown in Fig. 1, the prepared SBK glass samples with low Sb 2 O 3 content are transparent (SBK1, SBK2 and SBK3) and they turn yellow for higher Sb 2 O 3 content ones (SBK4, SBK5 and SBK6). As a result, it can be shown from Fig. 6 (a) that the absorbance increases with increasing the Sb 2 O 3 for the SBK glasses . It can be noticed that the Sb 2 O 3 -B 2 O 3 -K 2 O glasses exhibit a good transparence for wavelengths longer than 400 nm. It also can be noticed that with increasing the Sb 2 O 3 content, the UV absorption edge shifted into longer wavelengths (red shift).
Generally, the UV region optical absorbance edge are used for understanding the optical transitions and the electronic band structure for materials. It is known that there are two types of optical transitions, direct and indirect transitions. The indirect optical energy gap (E g ) of the prepared SBK glass samples have been estimated using the optical absorption method. The absorption coefficient (a) of the glass samples can be calculated from the following relation [20]: Where A is the optical absorbance and d is the thickness of the SBK glass sample. The optical energy gap (E g ) of the SBK glasses was calculated using Tauc's relation as following [28][29][30]: Absorbance (a.u.)  where B is a constant, m is the light frequency, h is the Planck's constant, E g is the optical band gap. The optical band gap energy (E g ) for the SBK glasses was estimated by extrapolating the linear part of the spectrum of h m versus (ah m) 1/2 as shown in Fig. 6b. Figure 7 shows the variation of the indirect optical energy gap (E g ) of the SBK glasses with the Sb 2 O 3 content. It can be shown that the optical energy gap of SBK glasses is decreasing from 4 to 2.63 eV with increasing Sb 2 O 3 content as shown in Table 1. This can be attributed to the increase in the nonbridging oxygens (NBOs) in the glass matrix with more Sb 2 O 3 content [31].
The refractive index (n) is a very important parameters that affected the electromagnetic wave propagation of the material. The refractive index for the SBK glasses was estimated and related to the indirect optical energy gap (E g ) from the following equation [35].
The variation of the refractive index values with the Sb 2 O 3 content for the SBK glasses is presented in Fig. 8. As given in Table 1, (n) values vary from 2.17 for sample SBK1 and with increasing Sb 2 O 3 content increase to 2.505 for SBK6. A higher value of refractive index value is obtained when the amount of nonbridging oxygen (which introduced by increasing the Sb 2 O 3 content in our glass) is higher than the bridging oxygen in the glass samples [36]. This can attribute to those of the non-bridging oxygens (NBOs) which have large electronic hyperpolarizability character in comparison with the bridging oxygens.
The molar refractivity (R m ) and molar polarizability (a m ) have been calculated as following [37,38]: As shown in Table 1 for SBK glasses, the values of molar refractivity (R m ) and molar polarizability (a m ) are found to increase with increasing Sb 2 O 3 content.
And, the optical energy gap values have been used to calculate the third-order nonlinear susceptibility v 3 (in e.s.u units) as follows [39]: The values v 3 for SBK glasses arere listed in Table 1. It can be shown that the third-order nonlinear optical susceptibility values increase with increasing Sb 2 O 3 content. This may be attributed to the decrease in the values of optical energy gap for the SBK glass samples. The samples SBK4, SBK5 and SBK6 show higher v 3 values than that of pure silica glass (2.8 9 10 -12 e.s.u), which means that the SBK samples with higher Sb 2 O 3 content are promising for nonlinear optical devices.

Density, molar volume, oxygen molar
volume and oxygen packing density.
The change in glass structure can be also investigated through estimation some of important parameters, such as density (q), molar volume (V M ), oxygen molar volume (V O ) and oxygen packing density values (OPD). These parameters consider a measure for any structure change as they are affected badly by structure softness, compactness, cross-linking, etc. For all the SBK glasses, the density was experimentally estimated and calculated through the Archimedes method. The measurements were performed at room temperature with the aid of a digital balance of high sensitivity and using toluene with density 0.861 g/cm 3 as an immersion liquid. For each SBK glass sample, the average value of four separate measurements was taken to minimize the random error. The glass sample was weighted in air (W air ) and in toluene (W toluene ). The density (q exp ) was estimated using the following equation, Molar volume (V M ), Oxygen molar volume (V O ) and Oxygen packing density (OPD) of the SBK glasses were calculated as following: M i and X i is the molecular weight and molar fraction of each component i respectively, n i is the oxygen atoms number in each constituent oxide and C is the number of oxygen atoms at each glass composition [40,41].
As shown in Fig. 9 the measured (q exp ) of the SBK glasses are found to increase with increasing the Sb 2 O 3 concentration. The measured densities value varies from 2.241 gm/cm 3 for SBK1 sample to 4.273 gm/cm 3 for SBK6 sample as shown in Table 3. This increase in density value with increasing the Sb 2 O 3 concentration can be a result of the replacement of Sb 2 O 3 with high molecular mass (291.52 gm/mol) with B 2 O 3 that has low molecular mass (69.62 gm/mol) [18]. As shown in Fig. 1 the glass color turns yellow with higher Sb 2 O 3 , which also indicated the glass density change. Figure 9 also depicted the molar volume values for the SBK glasses that were estimated according to the Eq. (9) using the measured densities. It's obvious that the molar volume (V M ) also increases with increasing  Table 3). This increase in molar volume values for the SBK glasses can attributed to larger ionic size of Sb 3? (76 pm) ions compared to that of B 3? (23 pm) [18] and to the larger bond length of Sb-O (1.932 A o ) compared to the bond length of B-O (1.372 A o ) [42]. The variation of both oxygen molar volume (V O ) and oxygen packing density (OPD) values with Sb 2 O 3 concentration is depicted in Fig. 10. The oxygen molar volume value shows increase with increasing the Sb 2 O 3 concentration, their values vary from 14.3 cm 3 /mol for SBK1 to 18.3 cm 3 /mol for SBK6 (showed in Table 3). While the oxygen packing density (OPD) values shows opposite behavior. (OPD) decrease with increasing the Sb 2 O 3 concentration, their values vary from 69.9 mol/l for SBK1 to 54.60 mol/l for SBK6 as shown in Table 3. The (OPD) decrease because of increasing the molar volume (V M ), hence the Oxygens number remain the same by substituting B 2 O 3 with Sb 2 O 3 .
The theoretically predicted densities (q theor ) were calculated using the densities of the glass sample constituent oxides according to their appropriate concentrations as follows: where i is the index of the oxide; X i and q i are the molar fraction and density of the ith oxide, respectively. As shown in Table 3, the theoretically predicted density is also increase with increasing the Sb 2 O 3 concentration as we mentioned above because of the higher atomic mass of Sb 2 O 3 compared to that of B 2 O 3 . The theoretically predicted density value varies from 2.48 gm/cm 3 for SBK1 sample to 4.04 gm/cm 3 for SBK6 sample. The experimental density shows higher value than the theoretical one, except in SBK1 (the behavior is reversed). To clarify this manner, we should look to the molar volume of

Radiation shielding properties of SBK glasses
Some shielding parameters have been evaluated using Phy-X/PSD online software [43] to characterize the Gamma radiation shielding ability for SBK glasses. The mass attenuation coefficient, MAC, is very important parameter that characterize the probability of photons to interact the glasses and it is the basic tool to estimate the different shielding parameters and can be calculated with the known of glass density (q) as following [43,44]: Figure 11 shows the MAC of the SBK glasses in the photon energy ranged from 0.015 to 15 MeV. As shown in Fig. 11, MAC values of some traditional and commercial glasses are also included for comparison.  Table 4, which represents the absorption edges and atomic numbers of the constituent elements of the investigated glasses [45]), which resulted the discontinuity in the attenuation curve for (SBK2-SBK6) glasses. SBK6 sample has MAC values close to that of the Barite and higher MAC values than that of some commercial (RS-253-G18) and ordinary glasses (Ferrite, Chromite and magnetite), which means that SBK6 sample is the best for shielding applications among the investigated SBK glasses. The tenth (TVL) and half-value layer (HVL) also are two important parameters, to determine the glass thickness required to can attenuate the radiation intensity to about 10% and 50% of its initial intensity, respectively [43]. They can be calculated as following: The mean free path (MFP) is a significant parameter to characterize the glass radiation shielding feature, lower MFP value is the best for radiation shielding and it can evaluated as following [43]: Hence, HVL decreases from 0.036 to 0.0046 cm at 0.015 MeV as the Sb 2 O 3 concentration increases in SBK1 to SBK6 glasses; which indicate that increasing the Sb 2 O 3 concentration enhance the radiation shielding feature of the prepared glasses. It has been concluded that the SBK6 glass sample is the best between SBK investigated glasses for radiation shielding because it has the smallest HVL, TVL and MFP value, since it possesses the highest density.
Furthermore, the fast neutron removal cross section (FNRCS) (RR) is a factor used to characterize Table 4 Photon energies (in MeV) of absorption edges and atomic number Z of the constituent elements under investigations [45] Element Z M 1 L 3 L 2 L 1 K The tested samples Fig. 15 The fast neutron removal cross section, FNRCS of the studied glasses (SBK1-SBK6) in comparison with FNRCS of other traditional and commercial glasses how far the material is capable to attenuate neutrons. Nuclear fission, neutron capture, nuclear spallation processes, and elastic and inelastic scattering are some of the ways that neutrons and matter may interact. The following equation may be used to calculate the FNRCS (R) parameter, which is used to gauge a material's neutron attenuation capacity [43,44]: Here, (RR/q) I and q i are the mass removal cross section (MRCS) and partial density of the i th constitute element, respectively. The MRCS values were according to the literatures [46,47]. The estimated values of FNRCS are illustrated in Fig. 15, the FNRCS values of SBK1, SBK2, SBK3, SBK4, SBK5 and SBK6 glasses are 0.087, 0.092, 0.095, 0.091, 0.094 and 0.092 cm -1 , respectively. It is shown by the graph that FNRCS of the investigated glasses are higher and, therefore, better for neutrons protection than some commercial glasses (RS-253-G18, RS-520 and RS-360).

Conclusions
The influence of Sb 2 O 3 on the optical, physical, and structural properties was investigated for the ternar-yQuery Sb 2 O 3 -B 2 O 3 -K 2 O glass system. The SBK glass sample with low Sb 2 O 3 content is transparent and it turn yellow for higher Sb 2 O 3 content. The optical energy gap of SBK glasses is decreasing from 4 to 2.63 eV with increasing Sb 2 O 3 content due to the increase in the non-bridging oxygens (NBOs) in the glass matrix with more Sb 2 O 3 content. The refractive index values vary from 2.17 for sample SBK1 and with increasing Sb 2 O 3 content increase to 2.505 for SBK6.
The molar refractivity (R m ), molar polarizability (a m ) and the third-order nonlinear optical susceptibility values v 3 have been calculated. Their values are found to increase with increasing Sb 2 O 3 content. Densities, molar volume, oxygen molar volume of the SBK glasses are found to increase with increasing the Sb 2 O 3 concentration, while oxygen packing density decreases. Glass sample with higher Sb 2 O 3 concentration is the best between the studied SBK glasses for radiation shielding. Hence, SBK6 sample has higher MAC values than that of some commercial (RS-253-G18) and ordinary glasses (Ferrite, Chromite and magnetite).
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