JOURNAL OF MATERIALS SCIENCE 30 (1995) 724-728 Optical, infrared and DSC studies of sodium tetraborate glasses containing copper oxide A. A. KUTUB Physics Department, Umm AI-Qura University, P. O. Box 3711, Makkah, Saudi Arabia The optical absorption, density, DSC and infrared absorption spectra of a series of sodium tetraborate glasses are measured as a function of copper content up to 5 reel%. It is found that the addition of CuO shifts the fundamental absorption edges towards lower energies in the range from 6.17-3.48eV. The addition of CuO does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium tetraborate glass. DSC measurements showed endothermal peaks varying from 486-476 ~ depending on the CuO content. 1. Introduction As a part of a continuing study of transition metal ions in glasses [1-3], the results of a study of Cu 2 + ions in the sodium tetraborate glass system are reported here. Oxide glasses containing transition metal ions were first reported in 1954 [4]. Several transition metal oxides when heated with glass- forming substances such as GeO2, B203, SiO2, TeO2 and P205, form glasses on quenching from the melt. The loss of oxygen from the melt produces lower-valency transition-metal ions and indeed the electronic conduction in these glasses is associated with a hopping of electrons from reduced to normal valency ions as discussed in detail by Mott [5]. A great deal has been carried out on many glass systems including a number of glasses based on sodium tetraborate [6-10]. The present work reports results of optical, infrared absorption spectra and differential scanning calori- metry (DSC) measurements on sodium tetraborate glasses with low concentrations of copper. The ab- sorption data were analysed in the light of existing theories on optical absorption in amorphous semicon- ductors. 2. Experimental procedure 2.1. Glass preparation Homogeneous glass samples of the composition (mol%)(NazB4OT)lOO_x-(CuO)x where x varied from 0 to 5 reel% (Table I) were prepared from chemically pure grades of material according to their molar com- position in an alumina crucible. A typical melt con- tained some 30 g of material. In order to reduce a tendency to volatilization the crucible was initially heated for 1 h at 300 ~ and then transferred to an- other furnace maintained at 900 ~ for 1 h. The melt was stirred frequently, using an alumina rod. The melt was finally poured on to a clean stainless steel plate and cast into a disc shape of diameter 1.5 cm and 2 mm thickness. The disc was immediately transferred to another furnace for annealing at 300 ~ for 1 h. The furnace was then switched off to allow it to cool down gradually to room temperature. The glass samples were polished using diamond paste down to a minimum grit size of 0.1 lain. X-ray diffraction measurements confirmed the glassy nature of all the glass samples examined. Thin blown films of the glasses were pre- pared by dipping an alumina tube into the molten material, collecting a small amount of glass melt on the end of the tube, and blowing it into the air. Films ranging in thickness from 1 to 10 lam were obtained. The densities of the glass samples were measured at room temperature by the displacement method using xylene as the immersion liquid and a single pan bal- ance of 10-4g sensitivity. 2.2. Optical measurements Optical measurements for thin films and bulky glasses were carried out at room temperature in the wavelength range 185-900 nm using a Varian model Cary 2390 spectrophotometer. In the low absorption region (e < 104 cm-1) for thin film glasses~ multiple interference effects were well pronounced and use of this was made in determining the thickness of the films. The infrared absorption measurements were made for powdered glass samples using an SP3-100 Pye Unicam double-beam infrared spectrophotometer. The glass samples were ground in a clean mortar to a fine powder. A few milligrams of the glass powder were mixed and ground with a relatively large quanti- ty of KBr. KBr pellets transparent to infrared were formed by pressing the mixture at 10 tons for a few minutes. 724 0022-2461 9 1995 Chapman & Hall