_{2}O

_{5}(ZnO, PbO) SrO FeO

^{1}

^{2}

^{1}

^{1}

^{1}

^{2}

The AC conductivity and dielectric parameters of the glassy system of (70-_{2}O_{5}· _{2}O_{5}·

Transition metal (TM) oxide glasses have been of great interest and have drawn much attention in recent years due to their possible technological applications in memory switching, electrical threshold, optical switching devices, and so forth [

Although the transition metal ion glasses based on conventional network formers, such as P_{2}O_{5}, GeO_{2}, and SiO_{2} have been studied extensively [_{2}O_{5} glasses is well established, their structure has been studied relatively little and as a result there is no clear picture as to the exact nature of the oxygen polyhedral surrounding the vanadium atoms or of the role played by the second component. Even in the case of pure V_{2}O_{5} glass it has been reported in the literature [^{5+} ions exhibit both 4- and 5-fold coordination states, which is related to the sample preparation conditions.

A critical analysis of this problem has been published by Wright [

These types of glasses exhibit mixed electronic (electrons hopping along V^{4+}-O-V^{5+} paths) and ionic (Sr^{2+} ions) conductivity. Glasses with such mixed electrical conductivity attract scientific interest because of potential applications as solid electrolytes in electrochemical devices such as batteries, chemical sensors, and smart windows.

The unconventional TMO glasses were prepared by the conventional melt quenching method on the basis of molecular formula [(70-_{2}O_{5} ·

For electrical measurements, the annealed samples were polished to obtain disk shape samples with 2 mm thickness and 7 mm diameter. Good electrical content was achieved by painting the faces of the samples with an air-dried silver paste. The temperature of the sample was measured using digital thermometer.

The AC conductivity ^{−12} F/m).

The experimental results of the AC conductivity of (70-_{2}O_{5}·

Frequency dependence of AC conductivity (

Frequency exponent

Frequency exponent

In most amorphous materials a polaron is formed due to the lattice distribution [

Hopping between two energetically favorable sites over a potential barrier may take place in TM oxide glasses. In the CBH model for AC loss, first introduced by Anderson and Drago [

The temperature dependence of the dielectric constant (_{2}O_{5} ·

The dielectric constant

The variation of real (_{2}O_{5} ·

the dielectric constant (

dielectric dispersion is observed clearly from 300 K,

the variation of the dielectric constant (

Typical plots of variation of (a) dielectric constant (

These results agree with all the studied samples (70-_{2}O_{5} ·

Figure _{2}O_{5} ·

Typical plots of variation of (a) dielectric constant (

Figures _{x}_{x}_{10} and P_{10}, respectively. Also it was observed peaks in the

Typical plots of variation of (a) dielectric constant (

Typical plots of variation of (a) dielectric constant (

In the studied samples (70-_{2}O_{5}·

Figures _{0}. These results agree with all samples (70-_{2}O_{5} ·

Figures ^{5} Hz). It is clear from these figures that the dielectric constant (_{2}O_{5} ·

Variation of (a) dielectric constant and (b) dielectric loss with temperature at 5 × 10^{5} Hz frequency for the (70-_{2}O_{5} ·

Figures

Variation of (a) dielectric constant and (b) dielectric loss with concentration for the (70-_{2}O_{5} ·

Typical plots of variation of imaginary (

Mott et al. [_{o} → D_{+} + D_{−} is exothermic, then only paired, defect states are found in the gap. Since these defect states are paired in which half of the charge carriers (dangling bonds) are positively charged and the remaining half are negatively charged, the paired states analogous to electric dipoles and hence the entire system may be considered to be virtually a dipolar system. At low temperature, one would expect a large distribution of relaxation times because of hindered rotation of these dipoles. Therefore, a Debay-type relaxation may lose its significance at such low temperatures. A very large distribution of relaxation times should give a dielectric loss which would be almost independent of temperature. As the temperature increases, the dipoles slowly attain freedom of rotation, and, therefore, a Debye-type relaxation should be observable. Under such circumstances, the dielectric loss is expected to become temperature and frequency dependent.

According to Debye’s theory [_{2}O_{5}·

Dielectric relaxation parameters of (70-_{2}O_{5}·

Samples | Relaxation time from Cole-Cole | ||||||||
---|---|---|---|---|---|---|---|---|---|

Z_{0} | 343 K | 45 | 4100 | 2.4 × 10^{−5} | 1.16 × 10^{−9} | 3.5 × 10^{−4} | 0.61 | 0.41 | 0.35 |

Z_{5} | 383 K | 35 | 8300 | 2.7 × 10^{−4} | 6.67 × 10^{−12} | 4.5 × 10^{−3} | 0.5 | 0.43 | 0.43 |

Z_{10} | 383 K | 36 | 18700 | 3.3 × 10^{−4} | 2.2 × 10^{−12} | 3 × 10^{−5} | 0.51 | 0.53 | 0.52 |

Z_{15} | 433 K | 40 | 21100 | 2.5 × 10^{−4} | 1.84 × 10^{−9} | 3 × 10^{−4} | 0.59 | 0.70 | 0.69 |

P_{5} | 373 K | 42 | 150 | 5.4 × 10^{−6} | 6.55 × 10^{−12} | 5.2 × 10^{−2} | 0.5 | 0.53 | 0.48 |

P_{10} | 403 K | 46 | 140 | 3.5 × 10^{−6} | 3.58 × 10^{−11} | 1.35 × 10^{−4} | 0.31 | 0.65 | 0.53 |

P_{15} | 383 K | 20 | 100 | 1.4 × 10^{−3} | 1.69 × 10^{−9} | 3.1 × 10^{−4} | 0.60 | 0.65 | 0.56 |

The AC response of the investigated samples (70-_{2}O_{5}·

Typical plots of variation of imaginary (

Typical plots of variation of imaginary (

The variation of relaxation frequency with

The peak positions of

The variation of relaxation frequency with

Cole-Cole diagram for the _{x}

Cole and Cole showed that, if a dielectric system has a distribution of relaxation time, the curve obtained by plotting _{x}_{2}O_{5} ·

The dielectric constant and loss data of the samples (

The dielectric parameters and the electrical properties of the studied glass systems were found to be temperature and frequency dependent. A dielectric dispersion was found to occur in these two systems. Such dispersion was supposed to be due to the dc conduction loss as well as to the dipolar type of the defects in the studied samples. The dielectric constant and the dielectric loss show slight increase with the addition of ZnO until it reached a maximum value in the sample containing 10% mole but on adding PbO to the vanadate network, they show a decrease to reach its smallest value at 15% mole PbO. A possible explanation for glasses containing ZnO is given in terms of hopping of charge carriers over a potential barrier between charged defect states. The increase of the dielectric parameters with zinc oxide concentration can be understood in terms of the decreased density of defect states. In glasses containing PbO, it can be stated that the density of defect states increased when lead oxide concentration was increased.

On increasing the concentrations of zinc or lead oxides, an increase in the activation energies was observed, which may be due to the decrease of the density of defect states and/or to the decrease of the disorder in the mobility edge. Complex relative permittivity data have been analyzed using the dielectric modulus (

The dielectric constant and loss data of all glasses were fitted to Cole-Cole functions, where the parameter ^{−2} and 3 × 10^{−2} s.

_{2}O

_{5}