Network structure of molybdenum lead phosphate glasses: Infrared spectra and constants of elasticity Yasser B. Saddeek a,b,n a Physics Department, Faculty of Science, Al-Azhar University, Assiut 71524, Egypt b Physics Department, Faculty of Science, Majmaa University, Zulfi, Saudi Arabia article info Article history: Received 14 March 2010 Received in revised form 7 November 2010 Accepted 12 November 2010 Keywords: Phosphate glasses IR Density Elastic properties DSC Crystallization kinetics abstract Molybdenum lead phosphate glasses doped with La 2 O 3 of the system xMoO 3 –5La 2 O 3 –50P 2 O 5 – (45  x)PbO, with 0 rx r25 mol%, have been synthesized and studied by FTIR, ultrasonic and differential scanning calorimetry (DSC) in order to investigate the role of MoO 3 content on their atomic structure. The constants of elasticity and Debye temperatures of the glasses have been investigated using sound velocity measurements at 4 MHz. According to the IR analysis, the vibrations of the phosphate structural units are shifted towards higher wavenumbers associated with the formation of bridging oxygens. The change in density with MoO 3 content reveals that the molybdate units are less dense than the lead units. The observed compositional dependence of the constants of elasticity is interpreted in terms of the effect of MoO 3 on the different phosphate bonds. It is assumed that MoO 3 plays the role of a former by increasing the ultrasonic velocity and the constants of elasticity of the phosphate glasses. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Phosphate based glasses are both scientifically and technolo- gically important materials because they generally offer some unique physical properties better than other glasses because of the linked PO 4 structural units with covalent bonding in chains or rings by bridging oxygens [1–4]. These glasses have poor chemical durability that often limits their usefulness that can be improved by the substitution of various oxides such as lead oxide [5,6], have low melting and glass transition temperatures [7,8], high electrical conductivity [9], high thermal expansion coefficient [10], and high ultraviolet (UV) transmission [11,12]. These properties making them useful candidates for fast ion conducting materials [13], laser host matrices after doping with rare-earth elements [14,15], glass- to-metal seals [16], and for the immobilization and disposal of nuclear waste were reported [17,18]. Investigations of lead phosphate glasses have revealed that the modifier/former role of PbO depends on PbO concentration in the glass composition x PbO (100  x)P 2 O 5 with 0 rx r85 mol%. The created P–O–Pb bonds along with the high ionic field strength and polarizability of Pb 2+ ions control the physical properties of lead phosphate glasses. Depending on the studied glass system, the Pb 2+ ions show an intermediate character between former and modifier. As a glass former, PbO enters the network with PbO 4 structural units by sharing the corners of phosphate network which in turn form P–O–Pb linkages. When PbO acts as network modifier, Pb is octahedrally coordinated and behaves like any other conventional alkali oxide modifier [19,20]. On the other hand, there has been an enormous amount of researches on improving the physical proper- ties of phosphate glasses that make them potential materials for electro-optical applications by introducing a number of transition metal oxides like MoO 3 , Ag 2 O, or PbO to form binary or ternary glass systems. It was revealed that, molybdenum–phosphate glasses belong to a group of glasses which incorporate distorted octahedral structural units [MoO 6 ] or tetrahedral structural units [MoO 4 ] within the glass network [21–26]. Therefore, the objective of the present study is to investigate the structural influence of MoO 3 on the lead phosphate glasses doped with La 2 O 3 through a detailed investigation on IR coupled with the constants of elasticity. 2. Experimental procedures The starting materials to obtain the x MoO 3 –5La 2 O 3 –50P 2 O 5 – (45  x) PbO glass system with 0 rx r25 mol% were (NH 4 ) 2 HPO 4 , PbO, La 2 O 3 , and MoO 3 of reagent grade purity. The samples were prepared by weighing suitable proportions of the components, the powder was mixed and then was melted in a platinum crucible at 1373 K for 1 h. Glasses in bulk form were produced by pouring the melts on preheated stainless-steel molds followed by annealing at Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2010.11.041 n Correspondence address: Physics Department, Faculty of Science, Al-Azhar University, Assiut 71524, Egypt. Tel.: + 20 103620536. E-mail address: ysaddeek@gmail.com Physica B 406 (2011) 562–566