1. Introduction The titanium oxide is a typical n-type semiconductor. It has three crystalline forms found in nature: brookite, anatase

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1. Introduction
The titanium oxide is a typical n-type semiconductor. It 
has three crystalline forms found in nature: brookite, anatase, 
and rutile. The first of them is quite rare. Rutile is stable at 
high temperature while anatase does not show this feature. 
Temperatures transitions between the different phases are as 
follows [1-3]:
• 
brookite – rutile; 500-600°C,
• 
anatase – rutile; 850°C.
rutile 
anataze
brookite
Fig. 1. The structures of the elementary cells of crystalline forms of 
titanium dioxide
Crystal structure of titanium oxide depends on the 
arrangement of octahedrons and the way in which individual 
units TiO6 are connected. For rutile, neighboring octahedra 
share with each other one corner and arranged along the long 
axis with mutual twisting equal to 90º. In the case of the form 
of anatase, the next octahedra shared a common edge and in 
brookite point of attachment are the both corner and edge [1-
3]. The research works most concern anatase and rutile. Rutile 
is built of parallel chains of octahedrons, a little deformed, 
but each of them is connected to the ten neighboring the same 
units. Octahedrons in the anatase have a warpage of the prism, 
and each octahedron is connected to eight other. In the anatase, 
Ti-Ti distance is longer, and Ti-O shorter than it is in the rutile 
form.
Titanium dioxide is a non-toxic semiconductor with 
a wide band gap, which is commonly used as a white pigment 
in toothpaste, paints, paper, etc. The material has unique 
properties because of its excellent chemical stability. It can 
be used as a photocatalyst in the splitting of water induced by 
UV radiation. The holes potential in the valence band is low 
enough to oxidize most of the organic compounds, which is 
causing a wide range of applications of titanium dioxide on the 
self-cleaning surfaces. In comparison to other semiconductors 
with similar energy bandgap energy is not subject to 
photodegradation under the influence of the excitation [4-8]. 
The advantages of titanium dioxide thin films is a large 
value of refractive index (over 2.3) and very good transparency 
(over 90%) over a wide spectral range (from about 320 to about 
6000 nm). In addition to good optical properties of TiO
2
it has 
also many other desirable properties such as high mechanical 
resistance, and long term stability. Therefore, the titanium 
oxide thin films are widely used as anti-reflective coatings in 
optics and photovoltaics [9-12].
In the dye-sensitized solar cells (DSSC) anatase titanium 
dioxide form is most often used. To increase the active surface 
of the light absorption, a semiconductive oxide layer has 
the nanocrystalline structure. If the surface is smooth and 
is covered with a monolayer of dye, absorbed of incident 
monochromatic light is less than 1%. For the use in a DSSC, 
titanium dioxide must have an n-type conductivity, order to 
conduction electrons transferred from the sensitizer [5]. This 
oxide is considered as the best material to cover the DSSC 
electrode due to the width energy bandgap and the position of 
the edge of the conduction band sufficiently low in relation to 
Arch. Metall. Mater., Vol. 61 (2016), No 2, p. 833–836
DOI: 10.1515/amm-2016-0140
L.A. DobrzAński*, M.M. szinDLer*