الفهرس 
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Abstract
The present study deals with an experimental investigation for
(76V20S-24P20S)I_x(Ll3P04)Xglass to follow up some of their physical
properties.
The glass samples (76V2Os- 24P 2Os) I-X(Ll , P04)x(where x= 0.0,
0.01 , 0,02 0,01 and 0,15 ) have been prepared by quenching the melt to
room temperature .
Characterization of the glasses has been done using X- ray diffraction
and differential thermal analysis (DTA).X-ray diffraction study for all
samples illustrated the amorphous nature of glasses. Differential thermal
analysis (DTA.) reveals that the characteristic glass transition temperature
of the samples glass ( Tg ) shifts toward higher temperature with increasing
the lithium phosphate content.
The de electric conductivity of the glass samples was studied over a
temperature range from room temperature to 593K.The general behavior
shows two regions, one at relatively low temperature range and the other
one at the higher temperature range. At the high temperature range ( abOve
8nl2), the conduction mechanism is explained according to the hopping of
small polaron to the nearest empty sites . In the temperature range below
8nl2 , the conduction process could be explained as a contribution of two
processes . The first is the electron hopping between filled and empty
localized states which dominate at low temperature range and the second is
due to small polaron hopping .
An increase of the activation energy with increasing Lithium
Phosphate was obtained which was attributed to :
I) An increase of the phosphate group in the glass matrix which reduces the
vanadium fraction and subsequently the electrical co ductivity.
2) The glass hydration which leads to a contrib ion of protons in
conduction process in the glasses .
3) The increase of lithium ion conduction in the glass.
The current - voltage ( I - V ) characteristic 0 the glasses has been
studied as a function of both temperature and Lithi phosphate content.
The I - V characteristic exhibits threshold switc . g with differential
negative resistance. It is found that the threshold voltag (VdJ decreases and
the threshold current ( lib ) increases with increasing te , while they
vary inversely with increasing lithium phosphate con nt. The behavior of
the Off - state region is analyzed according to PooI- F nkel effect besides
the joule heating . The switching to the negative res~ region has been
,
discussed according to the electrothermal model. The ~nduction process in
the negative resistance region are interpreted accor~ to the activation of
charge carrier under the influence of the high field ,the j~ule heating, and the
self generation of a.c signal in the conduction path filam~t .
,
The total conductivity (Oiot ) of the glasses are studied in the frequency
range ( 0.2 - 100 kHz ) and the temperature range (1290- 493 K) .The
conductivity - frequency dependence relation is divid¥ into two regions ;
One at low frequency while the other appears at relative~ higher frequency
range . The low frequency conductivity region refers to d.c conductivity
and is found to be strongly dependent on temperature . relatively higher
frequency conductivity region obeys a power law relation, u= A roS . The
obtained values of the power s lie in the range (0.5 :5; s :5; I ) in the case of
vanadium phosphate glass sample and that of low oflithium phosphate
content (0.01 ,0.02) which confirms the electron hopping between ”0+
and yS+ ions .The values ofs for the glass sample of the higher lithium
phosphate content, the values of s less than 0.5 confirm the domination
of ionic conductivity in the investigated glasses .
The frequency and temperature dependence of the dielectric
constant e’ , the dielectric loss s” and the dielectric loss tangent. Are
studied the dielectric constant and the dielectric loss decrease as the
frequency was increased for all glass samples . A slight decrease is
observed at low frequency range while a strong dependence appears at
higher frequency range . The dielectric constant increases slightly with
increasing temperature . The effect of frequency assists electron
hopping between v” and V5+ ions, while increasing temperature
causes the glassy network relaxes from which the ionic motion
becomes easier .
The bulk conductivity of the glasses is obtained by the complex
impedance technique. It increases with increasing temperature obeying
Arrhenious relation :
DBT = O”Bo exp ( - ED / ka T)
The obtained values of the activation energy Eb lie in the ~e
(0.348 - 0.467 eY ) . In addition the bulk conductivity is found to
decrease with increasing lithium phosphate content.