The middle infrared range, at the wavelength range of 3–5 mm, is
the most important atmospheric transmission windows and transparent
materials in this range are especially important for optical
applications [1]. It is well known that, transparent materials for optical
applications must provide maximum transmission and withstand the
thermal shock and abrasion. These materials must be isotropic and
easily fabricated at low costs. However, one ideal window satisfying
all the requirements does not exist and selection of an infrared window
is often based on compromises instead of choices [2–5].
Among window materials for IR applications (eg; ZnS, sapphire,
AlON and some glasses), germanate glasses have been of interest
due to the excellent combination of IR transparency, chemical
durability, and availability in desired shape and size [2–7]. However,
low mechanical properties (strength and elastic modulus) are the
major limitation of these glasses. One of reasonable approaches to
combat the above drawback is to convert germanate glasses to
germanate glass-ceramics, via controlled crystallization process.
Glass-ceramic technology is based on controlled nucleation and
growth of crystalline phases in certain glasses. This process has
several advantages over conventional powder-processed ceramics,
such as very low or null porosity, as well as uniformity and reproducibility
of microstructure [7–9]. As-precipitated crystalline
phases in glass matrix typically enhance the physical and mechanical
properties of prepared samples and sometimes lead to
entirely new combination of properties. In fact, low thermal expansion
coefficients, high thermal and chemical stability, high
mechanical properties and optical transparency are the most important
technological properties of glass-ceramics [3–5].
This paper focuses on the development and characterization of
transparent GeO2-PbO-MgO-MgF2 glass and glass-ceramics. In this
regard, the desired glasses were prepared using conventional melt
quenching technique and the structural and phase changes, during
melt quenching and annealing processes, were evaluated. Moreover,
the optical properties of prepared samples were analyzed
and values of the optical band gap and Urbach energy of prepared
glass-ceramics were established. Consequently, formation of
transparent GeO2-PbO-MgF2-MgO based glass-ceramics during
controlled crystallization process and optical characterization of
prepared glass-ceramics are the major novelty of this work.