The structural investigations of PbO–P2O5–Sb2O3 glasses with MoO3 as additive by means of dielectric, spectroscopic and magnetic studies
Introduction
P2O5 glasses have several advantages over conventional silicate and borate glasses due to their superior physical properties such as high thermal expansion coefficients, low melting and softening temperatures and high ultra-violet and far infrared transmission [1] and are also the materials of choice particularly for high power laser applications [2]. During the last two decades, phosphate glasses have been investigated extensively, yet there is still a great interest in developing new glasses suited to the demands of both industry and technology. Many phosphate glasses are prone to crystallization or devitrification either during processing or while put into applications where they may be held at high temperatures for longer periods. Further, the poor chemical durability, high hygroscopic and volatile nature of phosphate glasses prevented them from replacing the conventional glasses in a wide range of technological applications. In recent years, there has been an enormous amount of research on improving the physical properties and the chemical durability of phosphate glasses by introducing a number of glass formers and modifiers such as TiO2, V2O5, Al2O3, MoO3, Cr2O3, Ta2O3, Sb2O3, As2O3 etc., into P2O5 glass network [3], [4].
Among various phosphate glass systems, the alkali free PbO–P2O5 glass systems are known to be more stable against devitrification and moisture resistant. In contrast to the conventional alkali/alkaline earth oxide modifiers, PbO has the ability to form stable glasses due to its dual role; one as the modifier [5] if Pb–O is ionic and the other as the glass former [6], [7], if Pb–O is covalent. When Pb2+ ions are present in the glass as network formers, they impart a three-dimensional character to the glass. This fact accounts for the ability of PbO to form glasses up to 90 mol%. Clearly this peculiar behavior, which distinguishes lead from alkali and alkaline earth metals, depends on the electronic structure of the Pb2+ ion. In fact the easily polarizable valence shell of the Pb2+ ion strongly interacts with highly polarizable O2− ion, giving rise to a rather covalent Pb–O bond [8].
The addition of other heavy metal oxide like antimony oxide to the phosphate glasses, makes them suitable for potential applications in nonlinear optical devices (such as ultra-fast optical switches and power limiters), broad band optical amplifiers operating around 1.5 μm [9], [10], [11]. Further, since the frequencies of some of the vibrational groups of antimony oxide lie in the same regions of phosphate groups, it is expected that Sb2O3 mixes easily with the P2O5 network and makes the glass more stable against moisture. The antimony oxide participates in the glass network with the oxygen at three corners and the lone pair of electrons of antimony at the fourth corner in the glass network, the Sb–O distances ranges from 2.0 to 2.6 Å with the coordination number of Sb as 3.0 [12], [13].
MoO3-containing glasses have been the subject of many investigations due to their catalytic properties. The ions of molybdenum inculcate high activity and selectivity in a series of oxidation reactions of practical importance in the glass matrices [14]. A considerable number of interesting studies are available on the environment of molybdenum ion in various inorganic glasses [15], [16], [17], [18]. Mo–O bond in molybdenum hexavalent oxide is identified as significantly covalent. The molybdenum ion exists at least in two stable valence states, viz., Mo (V) and Mo (VI) in the glass network. Earlier ESR studies on the glasses containing molybdenum ions have identified the presence of octahedrally coordinated Mo (V) ions along with distorted octahedrons approaching tetragons [19], [20]. The ions of molybdenum act both as network formers with MoO42− structural units as well as network modifiers depending upon their concentration and nature of the host network. Quite a good number of studies on various physical properties viz., spectroscopic, ionic conductivity, dielectric properties etc., of some glass systems containing molybdenum ions are also available [21], [22], [23], [24].
The objective of the present study is to investigate the structural influence of molybdenum ions on PbO–P2O5–Sb2O3 glass network with a gradual decrease in the concentration of MoO3 through a detailed investigation on spectroscopic (optical absorption, Raman, IR and ESR) coupled with dielectric properties and magnetic studies.
Section snippets
Experimental
For the present study, a particular composition 40PbO–40P2O5−(16+x)Sb2O3:(4−x)MoO3 with nine values of x ranging from 0 to 4 were prepared. The details of the compositions chosen for the present study are presented in Table 1.
The analytical grade reagents of ammonium dihydrogen phosphate, PbO, Sb2O3 and MoO3 powders in appropriate amounts (all in mol%) were thoroughly mixed in an agate mortar and melted using a platinum crucible in the temperature range of 950–1000 °C in a PID temperature
Results
From the measured values of density d and calculated average molecular weight , various physical parameters of PbO–P2O5–Sb2O3:MoO3 glasses such as molybdenum ion concentration Ni, mean molybdenum ion separation Ri, are evaluated and are presented in Table 1.
Fig. 1 shows typical traces of differential thermal analysis of all the glasses under study. The curves exhibit an endothermic effect due to glass transition temperature Tg; the values of Tg are evaluated from the point of inflection of
Discussion
P2O5 is a well known network former with PO4 structural units with one of the four oxygen atoms in PO4 tetrahedron is doubly bonded to the phosphorus atom with the substantial π-bond character to account for pentavalency of phosphorous [34]. The PO4 tetrahedrons link together with covalent bonding in chains or rings by bridging oxygens. Neighboring phosphate chains are connected together by cross-bonding between the metal cation and two nonbridging oxygen (NBO) atoms of each PO4 tetrahedron. In
Conclusion
In conclusion, the analysis of the results of various studies, viz., optical absorption, ESR, IR and Raman spectra and dielectric properties of PbO–P2O5–Sb2O3 glasses added with different concentrations of MoO3, indicates that there is a possibility of conversion of a part of Mo6+ ions into Mo5+ ions, especially when the concentration of MoO3 is less than 1.0 mol%. Such ions (Mo5+ ions) mostly act as modifiers similar to Pb2+ ions and weaken the lead antimony phosphate glass network.
Acknowledgement
One of the authors, Mrs. G. Little Flower is grateful to the University Grants Commission, New Delhi for providing financial assistance in the form of a Research Project. She also wishes to thank the management of Maris Stella College, Vijayawada for their precious support and to Rev. Sr. Dr Theresiamma, the Principal of the same college for her appreciation and kindness.
References (62)
- et al.
J. Non-Cryst. Solids
(2000) - et al.
Mater. Res. Bull.
(2000) - et al.
Mater. Res. Bull.
(2001) - et al.
J. Non-Cryst. Solids
(1994) - et al.
J. Non-Cryst. Solids
(1996) - et al.
J. Non-Cryst. Solids
(1986) - et al.
Appl. Catal.
(1991) - et al.
J. Non-Cryst. Solids
(1983) - et al.
Solid State Ion.
(2000) - et al.
Chem. Phys. Lett.
(2003)
Mater. Lett.
J. Non-Cryst. Solids
Mater. Res. Bull.
Spectrochem. Acta
J. Phys.: Condens. Matter
Inorg. Chem.
Chem. Phys.
Spectrodum Acta Crystallogr. A
J. Non-Cryst. Solids
J. Solid State Commun.
J. Non-Cryst. Solids
Phys. Chem. Glasses
J. Mater. Sci.
Sov. Phys. Usp.
J. Mater. Sci.
J. Phys. D
Phys. Chem. Glasses
Phys. Status Solidi A
Cited by (65)
Thermal, optical, structural, and electrical properties of ZnO–MoO<inf>3</inf>–TeO<inf>2</inf> glasses
2023, Ceramics InternationalCitation Excerpt :Molybdenum oxide, is also a conditional glass forming compound but it can also act as network modifier. This behaviour is due to the fact that molybdenum in glass can be present in different oxidation states [2,3] – Mo6+ forms tetrahedra [MoO4] and also octahedra [MoO6] in MoO3 rich areas that both participate in the glassy network through their connections by bridging oxygen atoms [4–7]. On the other hand, Mo5+ ion forms [Mo5+O3]- structural unit that acts as a network modifier [3,7].
Optical properties of the B<inf>2</inf>O<inf>3</inf>–CdO–ZnO–Li<inf>2</inf>O glasses modified with MoO<inf>3</inf>
2023, Materials Today: ProceedingsThe efficacy of various thicknesses of float glasses for protection of gamma-radiation
2022, Radiation Physics and ChemistryHeavy metal oxide glasses and their optoelectronic applications (infrared transmission, luminescence, nonlinear optical susceptibilities, etc.)
2022, Metal Oxides for Optoelectronics and Optics-Based Medical Applications