D. R. Goyal

Investigation of optical absorption in Sb-Se glassy alloys

Optical absorption measurements were made on thin films of amorphous SbxSe100−x alloys 5<x<20 prepared by vacuum evaporation. These measurements were made on the as-prepared and annealed samples. It was observed that annealing affects the optical properties and causes a reduction in the energy range of tail states and an increase in the optical energy gap in all the alloys. The mechanism of optical absorption follows the rule of non-direct transitions. The results obtained for different samples were compared with each other. Similar to the activation energy of d.c. conductivity, the optical band gap before and after annealing was found to decrease with increasing Sb content in these alloys.

Structural and Physical Properties of Glasses

The structural and physical properties of xFe2O3-(40-x) B2O3-60V2O5 (0 ≤ x ≤ 20) glass system have been investigated. The samples were prepared by normal melt-quench technique. The structural changes were inferred by means of FTIR by monitoring the infrared (IR) spectra in the spectral range 600–4000 cm−1. The absence of boroxol ring (806 cm−1) in the present glass system suggested that these glasses consist of randomly connected BO3 and BO4 units. The conversion of BO3 to BO4 and VO5 to VO4 tetrahedra along with the formation of non-bridging oxygen’s (NBOs) attached to boron and vanadium takes place in the glasses under investigation. The density and molar volume of the present glass system were found to depend on Fe2O3 content. DC conductivity of the glass system has been determined in the temperature range 310–500 K. It was found that the general behavior of electrical conductivity was similar for all glass compositions and found to increase with increasing iron content. The parameters such as activation energy, average separation between transition metal ions (TMIs), polaron radius, and so forth have been calculated in adiabatic region and are found consistent with Mott’s model of phonon-assisted polaronic hopping.

Effect of Annealing on Optical Properties of Glasses

The Melt-quench method is used to synthesize zinc fluoroborate glasses with compositions (, 5, 10, 15, and 20). Optical characterization was carried out to examine the variation of optical bandgap energy () and urbach energy () with respect to the concentration for the samples annealed at different temperatures (, and ). Annealing shows its effect on the samples with the variations in the values of and . These variations are explained on the basis of formation of different molecular species like units, boroxol rings, and the change in the number of nonbridging oxygen atoms.

Effect of Stepwise Replacement of LiF by Bi2O3 and of Annealing on Optical Properties of LiF⋅B2O3 Glasses

Bismuth fluoroborate glasses with compositions 𝑥Bi2O3⋅(40−𝑥)LiF⋅60B2O3(𝑥=0,5,10,15,and20) are synthesized by melt-quench method. Optical characterization was carried out to examine variation of optical band gap energy (𝐸𝑔) and Urbach energy (𝐸𝑈) with respect to the concentration. It reflects the effect of stepwise replacement of non-oxide and less polarizable LiF by an oxide and more polarizable (Bi2O3) group on the optical properties of the samples. The value of 𝐸𝑔 decreases with increase in concentration of Bi2O3. The samples were subjected to annealing at different temperatures (300°C, 350°C, and 400°C), and the effect of annealing on the optical properties of various samples was again studied. Annealing affects remarkably the values of 𝐸𝑔 and 𝐸𝑈 in the samples with 𝑥=0.

Effect of Stepwise Replacement of Non-Oxide to Oxide Group on Structural Properties of ·LiF· Glasses

Bismuth fluoroborate glasses with compositions xBi2O3·(40 − x)LiF·60 B2O3 (x = 0, 5, 10, 15, and 20) are synthesized by melt-quench method. XRD pattern is obtained for all the samples to confirm their amorphous nature. FTIR spectroscopy is carried out for the reported samples. It reflects the effect of replacement of a non-oxide group (LiF) with an oxide group (Bi2O3) in the glass network, due to the presence of the various absorption bands and their shifting with such replacement, assigning a role of network modifier to Bi2O3. Density and molar volume show an increase in their values with increase in Bi2O3 concentration. Theoretical optical basicity is calculated for the reported samples, which shows a decreasing trend with the increasing concentration of Bi2O3.

Optical Properties of Alkaline Earth Ions Doped Bismuth Borate Glasses

The optical properties of glasses with composition xLi2O (30‐x) Bi2O3‐70B2O3; x = 0, 5, 10, 15 & 20 mol %, prepared by normal melt quench technique were investigated by means of UV‐VIS measurement. It was observed that the optical band gap of the present glass system decreases with increasing Li2O content up to 15 mol%, and with further increase in lithium oxide content i.e. x>15 mol% the optical band gap increases. It was also observed that the present glass system behaves as an indirect band gap semiconductor.

DSC and DC conductivity of ZnO.LiF.B2O3 glasses

Melt-quench technique has been used to prepare fluoroborate glasses with ZnO content and having compositions x ZnO. (40-x) LiF. 60 B2O3 (x = 0, 5, 10, 15 and 20). DSC characterization is carried out to observe glass transition temperature. Two glass transition temperatures are observed for each of the reported samples. Both transition temperatures are found to increase with increase in ZnO content. DC conductivity is examined with respect to temperature variations. Results show that the conductivity is ionic in nature and varies with the variations in ZnO concentration.

DSC and DC Conductivity of Bi2O3 · LiF · B2O3 Glasses

Fluoroborate glasses with Bi2O3 content and having compositions Bi2O3 · ()LiF · 60B2O3 ( = 0, 5, 10, 15, and 20) are prepared using melt-quench technique. DSC characterization is carried out to observe glass transition temperature. Two such temperatures are observed for each of the reported samples. DC conductivity of the reported samples is studied with the variation in temperature from 313 K to 413 K by dividing this range into three regions, namely, low-, intermediate-, and high-temperature regions. DC conductivity responses for these temperature regions are explained using different conductivity models.

Structural investigation of Li{sub 2}O-Bi{sub 2}O{sub 3}-B{sub 2}O{sub 3} glasses

The structural properties of x Li{sub 2}O(30-x)Bi{sub 2}O{sub 3}-70B{sub 2}O{sub 3}; x = 0, 5, 10, 15 and 20 mol %, glasses were investigated by means of FT-IR measurement technique. The IR analysis of the present glass system shows that with increase in lithium oxide content (x{ 15 mol %), the frequency bands shift towards higher wavenumber indicate the formation of Bridging Oxygens (BOs).The structural properties of x Li2O (30‐x) Bi2O3‐70B2O3; x = 0, 5, 10, 15 & 20 mol %, glasses were investigated by means of FT‐IR measurement technique. The IR analysis of the present glass system shows that with increase in lithium oxide content (x≤15 mol%), the frequency bands in the higher region shift towards lower wavenumber, suggest the conversion of BO3 to BO4 structural units, which in turn give rise to the formation of Non Bridging Oxygen’s (NBOs). For further increase in lithium oxide content (x>15 mol %), the frequency bands shift towards higher wavenumber indicate the formation of Bridging Oxygen’s (BOs).The structural properties of x Li2O (30‐x) Bi2O3‐70B2O3; x = 0, 5, 10, 15 & 20 mol %, glasses were investigated by means of FT‐IR measurement technique. The IR analysis of the present glass system shows that with increase in lithium oxide content (x≤15 mol%), the frequency bands in the higher region shift towards lower wavenumber, suggest the conversion of BO3 to BO4 structural units, which in turn give rise to the formation of Non Bridging Oxygen’s (NBOs). For further increase in lithium oxide content (x>15 mol %), the frequency bands shift towards higher wavenumber indicate the formation of Bridging Oxygen’s (BOs).