**7. 92Si samples composition results**

Figure 6 shows the macroscopic aspect of the 92Si samples, TT at the temperatures of 650, 700 and 750 °C. The based glass, completely transparent, becomes translucent for temperatures above 700 °C.

**Figure 6.** Photographs of the 92Si TT glasses (minor division = 0 1 mm).

The 92Si samples, TTE, were named as: 650A (sample TTE at 650 °C with an electric field of 100 kV/m), 650B (sample TTE 650 °C with an electric field of 500 kV/m) and 650C (TTE sample at 650 °C with an electric field of 1000 kV/m). The same designation was used in TTE samples at temperatures of 700 (700A, 700B ... ) and 750 °C. In figure 7, photographs of all samples subjected to those treatments can be seen.

The samples 650A, 700A and 750A (samples TTE with a field amplitude of 100 kV/m) have a macroscopic aspect very similar to the sample 650B. With the increase of the TET temperature and applying 500 kV/m and 1000 kV/m, all samples become translucent.

#### 332 Heat Treatment – Conventional and Novel Applications

Lithium Niobiosilicate Glasses Thermally Treated 333

The XRD spectra of the samples series treated at 650 °C (Fig. 9) shows that the increase in amplitude of the external electrical field favors the formation of the LiNbO3 crystalline phase. In the sample series treated at the temperatures of 700 °C and 750 ºC (Figs. 10 and 11) it was detected the presence of LiNbO3, SiO2 (quartz) and Li2Si2O5 crystalline phases. It is important

to refer that the Li2Si2O5 phase only appears in the samples thermo-electrically treated.

**Figure 10.** XRD spectra of the 92Si samples TET at 700ºC (+ LiNbO3; O SiO2 (quartz); x Li2Si2O5).

**Figure 9.** XRD spectra of the 92Si samples TET at 650ºC (+ LiNbO3).

**Figure 7.** Photographs of the TTE samples at 650, 700 and 750 ºC, with the applied field of (B) 500 kV/m and (C) 1000 kV/m (minor scale division = 1mm).

Figure 8 shows the XRD patterns of the 92Si samples thermal treated without the presence of the external electrical field (TT). It can be observed for the samples TT at temperatures above 700 °C the presence of diffraction peaks associated with the LiNbO3 crystalline phase. The sample TT at 800 °C also presents a second crystalline phase (SiO2, quartz). The X-ray diffraction was performed at room temperature on a Phillips X'Pert system, where the X-ray production is performed on a Cu ampoule, operating at 40 kV and 30 mA, emitting the monochromatic Kα radiation (λ = 1,54056 Å - graphite monochromator). In this system the sweep is continuous, from 10.025 up to 89.975 º (2θ) with a speed of 1.5 degrees per minute and with a step of 0.02 º. The identification of the crystalline phases was based on the database provided by the JCPDS (Joint Committee on Powder Diffraction Standards). The figures 9 to 11 present the XRD spectra of the samples TET at 650, 700 and 750 ºC, respectively.

**Figure 8.** XRD of the 92Si samples TT at 650, 700, 750 and 800 ºC (x LiNbO3; O SiO2-quartzo).

The XRD spectra of the samples series treated at 650 °C (Fig. 9) shows that the increase in amplitude of the external electrical field favors the formation of the LiNbO3 crystalline phase. In the sample series treated at the temperatures of 700 °C and 750 ºC (Figs. 10 and 11) it was detected the presence of LiNbO3, SiO2 (quartz) and Li2Si2O5 crystalline phases. It is important to refer that the Li2Si2O5 phase only appears in the samples thermo-electrically treated.

**Figure 9.** XRD spectra of the 92Si samples TET at 650ºC (+ LiNbO3).

332 Heat Treatment – Conventional and Novel Applications

and (C) 1000 kV/m (minor scale division = 1mm).

**Figure 7.** Photographs of the TTE samples at 650, 700 and 750 ºC, with the applied field of (B) 500 kV/m

650B 700B 750B

650C 700C 750C

Figure 8 shows the XRD patterns of the 92Si samples thermal treated without the presence of the external electrical field (TT). It can be observed for the samples TT at temperatures above 700 °C the presence of diffraction peaks associated with the LiNbO3 crystalline phase. The sample TT at 800 °C also presents a second crystalline phase (SiO2, quartz). The X-ray diffraction was performed at room temperature on a Phillips X'Pert system, where the X-ray production is performed on a Cu ampoule, operating at 40 kV and 30 mA, emitting the monochromatic Kα radiation (λ = 1,54056 Å - graphite monochromator). In this system the sweep is continuous, from 10.025 up to 89.975 º (2θ) with a speed of 1.5 degrees per minute and with a step of 0.02 º. The identification of the crystalline phases was based on the database provided by the JCPDS (Joint Committee on Powder Diffraction Standards). The figures 9 to 11

present the XRD spectra of the samples TET at 650, 700 and 750 ºC, respectively.

**Figure 8.** XRD of the 92Si samples TT at 650, 700, 750 and 800 ºC (x LiNbO3; O SiO2-quartzo).

**Figure 10.** XRD spectra of the 92Si samples TET at 700ºC (+ LiNbO3; O SiO2 (quartz); x Li2Si2O5).

Lithium Niobiosilicate Glasses Thermally Treated 335

**Figure 12.** Raman spectra of the 92Si samples TT at 650, 700 and 750 ºC. The Raman spectrum of

LiNbO3 crystalline powders is also presented.

**Figure 11.** XRD spectra of the 92Si samples TET at 750ºC (+ LiNbO3; O SiO2 (quartz); x Li2Si2O5).

Figures 12 to 15 show the Raman spectra of the free surface of the heat treated samples with or without external electrical field applied. It must be motes that no differences were detected between the spectra obtained on the free surface of the samples and fracture zones (bulk). This analysis was performed on a spectrometer T64000, Jobin Yvon SPEX using an argon laser operating at 514.5 nm. The Raman spectrum was obtained with a back-scattering geometry (back-scattering) between 100 and 2000 cm-1. The amplitude of the lens used was of 50x which allows a laser spot diameter on the sample of about 5 mm.

In all Raman spectra (Figs. 12 to 15), the bands centered at 630, 590, 435, 375, 335, 330, 325, 280, 265, 240 and 155 cm-1 are associated to vibrations of the NbO6 octahedrons [20;21;22]. The bands at 465, 415 and 130 cm-1 (sample 700C) are assigned to vibration of Si-O-Si bonds [23]. The broad band centered at 330 cm-1, observed in the samples treated in the presence of an electric field of 1000 kV/m (samples C), seems to be due to the overlapping of the bands centered at 335 and 325 cm-1. The band at 830 cm-1, detected in the samples treated at 650 °C, with no external field applied, are attributed to the vibrations of the Nb-O-Si bonds [20;21;22;23;24].

In the following figures (Figs. 16) SEM micrographs of the free surface of the samples treated with and without the presence of an external electrical field are presented. The scanning electron microscopy was performed in a Hitachi S4100-1, on the surface and fracture of the samples covered with carbon.

334 Heat Treatment – Conventional and Novel Applications

mm.

[20;21;22;23;24].

fracture of the samples covered with carbon.

**Figure 11.** XRD spectra of the 92Si samples TET at 750ºC (+ LiNbO3; O SiO2 (quartz); x Li2Si2O5).

Figures 12 to 15 show the Raman spectra of the free surface of the heat treated samples with or without external electrical field applied. It must be motes that no differences were detected between the spectra obtained on the free surface of the samples and fracture zones (bulk). This analysis was performed on a spectrometer T64000, Jobin Yvon SPEX using an argon laser operating at 514.5 nm. The Raman spectrum was obtained with a back-scattering geometry (back-scattering) between 100 and 2000 cm-1. The amplitude of the lens used was of 50x which allows a laser spot diameter on the sample of about 5

In all Raman spectra (Figs. 12 to 15), the bands centered at 630, 590, 435, 375, 335, 330, 325, 280, 265, 240 and 155 cm-1 are associated to vibrations of the NbO6 octahedrons [20;21;22]. The bands at 465, 415 and 130 cm-1 (sample 700C) are assigned to vibration of Si-O-Si bonds [23]. The broad band centered at 330 cm-1, observed in the samples treated in the presence of an electric field of 1000 kV/m (samples C), seems to be due to the overlapping of the bands centered at 335 and 325 cm-1. The band at 830 cm-1, detected in the samples treated at 650 °C, with no external field applied, are attributed to the vibrations of the Nb-O-Si bonds

In the following figures (Figs. 16) SEM micrographs of the free surface of the samples treated with and without the presence of an external electrical field are presented. The scanning electron microscopy was performed in a Hitachi S4100-1, on the surface and

**Figure 12.** Raman spectra of the 92Si samples TT at 650, 700 and 750 ºC. The Raman spectrum of LiNbO3 crystalline powders is also presented.

Lithium Niobiosilicate Glasses Thermally Treated 337

**Figure 14.** Raman spectra of the 92Si samples TET at 700 ºC. The Raman spectrum of LiNbO3 crystalline

powders is also presented.

**Figure 13.** Raman spectra of the 92Si samples TET at 650 ºC. The Raman spectrum of LiNbO3 crystalline powders is also presented.

336 Heat Treatment – Conventional and Novel Applications

**Figure 13.** Raman spectra of the 92Si samples TET at 650 ºC. The Raman spectrum of LiNbO3 crystalline

powders is also presented.

**Figure 14.** Raman spectra of the 92Si samples TET at 700 ºC. The Raman spectrum of LiNbO3 crystalline powders is also presented.

Lithium Niobiosilicate Glasses Thermally Treated 339

(b)

**Figure 16.** SEM micrographs of the 92Si samples: a) as-prepared; b) TT at 700 ºC; c) TT at 750 ºC.

(c)

(a)

with the increase in amplitude of the applied field (Fig. 17).

preferred direction.

It was observed in the SEM micrographs of the 92Si based glass (sample TT at 500 °C) the inexistence of particles. Increasing the treatment temperature an increase in the number of surface particles is induced. In the sample heat treated at 700 °C, without applying the external electric field (Fig. 16), particles showing a preferential growth direction were observed. On the surface of the sample TT at 750 °C (Fig. 16c), particle with a size of approximately 500 nm are observed and with a distribution similar to that observed in the sample TT at 700 °C. It must be notice that it was not detected in any sample of the 92Si series, the existence of particles in fracture zone (bulk). In the samples TET at 650 °C it was observed an increase in the size and number of the particles dispersed in the glass matrix,

In the sample 700A, the number of particles present on the surface, which during the TTE was in contact with the positive electrode, is greater than that the number observed on the opposite surface, but with similar sizes (~ 100nm). The sample 700B registered a particle size distribution similar to the one observed in the sample 700A, but with a larger size (~ 1 μm). Increasing the amplitude of the external electric field up to 1000 kV/m (sample 700C) it was observed the presence of particle aggregation in the two opposite surfaces of the sample. However, the number and size of those aggregates are larger in the surface that was in contact with the positive electrode. The growth of those aggregates seems to have a

**Figure 15.** Raman spectra of the 92Si samples TET at 750 ºC. The Raman spectrum of LiNbO3 crystalline powders is also presented.

338 Heat Treatment – Conventional and Novel Applications

**Figure 15.** Raman spectra of the 92Si samples TET at 750 ºC. The Raman spectrum of LiNbO3 crystalline

powders is also presented.

**Figure 16.** SEM micrographs of the 92Si samples: a) as-prepared; b) TT at 700 ºC; c) TT at 750 ºC.

It was observed in the SEM micrographs of the 92Si based glass (sample TT at 500 °C) the inexistence of particles. Increasing the treatment temperature an increase in the number of surface particles is induced. In the sample heat treated at 700 °C, without applying the external electric field (Fig. 16), particles showing a preferential growth direction were observed. On the surface of the sample TT at 750 °C (Fig. 16c), particle with a size of approximately 500 nm are observed and with a distribution similar to that observed in the sample TT at 700 °C. It must be notice that it was not detected in any sample of the 92Si series, the existence of particles in fracture zone (bulk). In the samples TET at 650 °C it was observed an increase in the size and number of the particles dispersed in the glass matrix, with the increase in amplitude of the applied field (Fig. 17).

In the sample 700A, the number of particles present on the surface, which during the TTE was in contact with the positive electrode, is greater than that the number observed on the opposite surface, but with similar sizes (~ 100nm). The sample 700B registered a particle size distribution similar to the one observed in the sample 700A, but with a larger size (~ 1 μm). Increasing the amplitude of the external electric field up to 1000 kV/m (sample 700C) it was observed the presence of particle aggregation in the two opposite surfaces of the sample. However, the number and size of those aggregates are larger in the surface that was in contact with the positive electrode. The growth of those aggregates seems to have a preferred direction.

Lithium Niobiosilicate Glasses Thermally Treated 341

**Ea(dc) (B) (kJ/mol)** 

650

650A 650B 650C

This adjustment presented graphically in figures 14 to 16 by the lines, allowed the calculation of the dc activation energy (Ea(dc) – table 1). It is observed, in all samples, the existence of at least two regions with different activation energies. The first (A), between 270 and 300 K, and the second (B), between 345 and 370 K. The activation energy associated with the conduction mechanism detected at higher temperatures (Ea(dc) (B), Table 1) decreases with the increase of the amplitude of the applied electric field, for the sample series treated at 700 and 750 °C. It is observed, with the exception of the sample 700A, that the activation energy of the process A (at lowest temperatures) is always lower than the Ea(dc) of the

650 128,48 ± 5,15 24,64 ± 1,19 79,98 ± 1,12 650A 2,04 ± 0,06 27,91 ± 1,09 62,66 ± 2,66 650B 3,03 ± 0,09 27,94 ± 1,40 77,56 ± 0,95 650C 36,46 ± 1,46 48,83 ± 0,72 64,22 ± 1,41 700 13,21 ± 0,55 46,47 ± 1,92 72,98 ± 0,78 700A 4,96 ± 0,21 32,63 ± 3,00 71,38 ± 3,97 700B 8,64 ± 0,29 66,35 ± 1,02 66,79 ± 0,83 700C 15,18 ± 0,47 100,18 ± 3,31 57,15 ± 0,99 750 12,39 ± 0,43 31,48 ± 0,29 51,02 ± 1,55 750A 6,09 ± 0,35 31,63 ± 0,68 82,08 ± 3,19 750B 21,71 ± 1,06 7,71 ± 2,08 79,26 ± 0,82 750C 393,87 ± 12,91 24,47 ± 2,59 62,88 ± 1,22 **Table 1.** dc conductivity (σdc), at 300 K, dc activation energy (Ea(dc) ) for the: A - low temperature region

**Figure 18.** The dc conductivity (σdc , in logarithm scale) in function of 1000/T, for the 92Si samples

2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 **1000/T [K-1]**

**Ea(dc) (A) (kJ/mol)**

process B.

treated at 650 ºC.





**ln(**σ**dc) [Sm-1]**




**Sample** σ**dc x 10-14**

(230-300 K); B – high temperature region (310-370 K).

**(**Ω**-1m-1)**

**Figure 17.** SEM micrographs of the samples 92Si TET: (a) 650C; (b) 700B; (c) 700C; (d) 750C.

Increasing the amplitude of the external electrical field, in the TET at 750 °C, it was observed an increasing in the number of particles but with a reduction in their size. Samples 750A and 750B have particles with an average size of 300 and 250 nm, respectively. The sample 750C presents particles with a maximum size of ~ 50 nm. These particles tend to aggregate themselves.

The dependence of the dc conductivity, in logarithm scale (ln(σdc)), with the temperature of measurement, for the samples TT at 650, 700 and 750 °C, with or without external electrical field applied, is shown in figures 18 to 20. All samples exhibit, for temperatures below 270 K, dc conductivity values (σdc) lower than 10-15 Sm-1. The sample 750C shows the highest σdc value (2.63x10-9 Sm-1), at the temperature of 370 K. With increasing the treatment temperature, the σdc measured at 300 K, decreases. These measurements also showed that the σdc is lower in samples treated with an electric field of 100 kV/m of amplitude (samples 650A, 700A and 750A) than in the samples treated without the presence of the external electrical field. In all sample series (650, 700 and 750), the increase of the amplitude of the electric field applied during the heat treatment induces an increase in σdc (Table 1).

The dependence of the σdc with the measurement temperature was adjusted by the Arrhenius equation [25;26;27] -

$$
\sigma\_{dc} = \sigma\_0 e^{\left(-\frac{E\_A}{kT}\right)}
$$

This adjustment presented graphically in figures 14 to 16 by the lines, allowed the calculation of the dc activation energy (Ea(dc) – table 1). It is observed, in all samples, the existence of at least two regions with different activation energies. The first (A), between 270 and 300 K, and the second (B), between 345 and 370 K. The activation energy associated with the conduction mechanism detected at higher temperatures (Ea(dc) (B), Table 1) decreases with the increase of the amplitude of the applied electric field, for the sample series treated at 700 and 750 °C. It is observed, with the exception of the sample 700A, that the activation energy of the process A (at lowest temperatures) is always lower than the Ea(dc) of the process B.

340 Heat Treatment – Conventional and Novel Applications

themselves.

Arrhenius equation [25;26;27] -

**Figure 17.** SEM micrographs of the samples 92Si TET: (a) 650C; (b) 700B; (c) 700C; (d) 750C.

Increasing the amplitude of the external electrical field, in the TET at 750 °C, it was observed an increasing in the number of particles but with a reduction in their size. Samples 750A and 750B have particles with an average size of 300 and 250 nm, respectively. The sample 750C presents particles with a maximum size of ~ 50 nm. These particles tend to aggregate

(a) (b)

(c) (d)

The dependence of the dc conductivity, in logarithm scale (ln(σdc)), with the temperature of measurement, for the samples TT at 650, 700 and 750 °C, with or without external electrical field applied, is shown in figures 18 to 20. All samples exhibit, for temperatures below 270 K, dc conductivity values (σdc) lower than 10-15 Sm-1. The sample 750C shows the highest σdc value (2.63x10-9 Sm-1), at the temperature of 370 K. With increasing the treatment temperature, the σdc measured at 300 K, decreases. These measurements also showed that the σdc is lower in samples treated with an electric field of 100 kV/m of amplitude (samples 650A, 700A and 750A) than in the samples treated without the presence of the external electrical field. In all sample series (650, 700 and 750), the increase of the amplitude of the

electric field applied during the heat treatment induces an increase in σdc (Table 1).

The dependence of the σdc with the measurement temperature was adjusted by the

*dc* σ σ*e*

0

*AE kT*

 − =


**Table 1.** dc conductivity (σdc), at 300 K, dc activation energy (Ea(dc) ) for the: A - low temperature region (230-300 K); B – high temperature region (310-370 K).

**Figure 18.** The dc conductivity (σdc , in logarithm scale) in function of 1000/T, for the 92Si samples treated at 650 ºC.

Lithium Niobiosilicate Glasses Thermally Treated 343

**650**

**650A**

**650B**

**650C**

the samples series treated at 650 and 700 °C, that Z'' decreases with the increase of frequency. In the frequency range used, the impedance (Z\*), the admittance (Y\*), the permittivity (ε\*) and the dielectric modulus (M\*) formalisms did not revealed the existence of dielectric relaxation(s). It must be noted that, for frequencies below 100 Hz, there is a high dispersion of the Z´´ values, which is associated with the sensitivity of the measuring

An adjustment of the Z\* spectrum was carried out using a complex non-linear least squared deviations method (CNLLS) associated with the electrical equivalent circuit model formed by the parallel between a resistor (R) and a constant phase element (CPE). This constant phase element is characterized by keeping constant the angle of the impedance as a function of frequency, i.e. the ratio between the real and imaginary part of the impedance is constant across the all frequency range. The impedance of this intuitive element (ZCPE) can be

> ( ) <sup>0</sup> 1 *CPE <sup>n</sup> Z Q j*ω

0.0E+00 5.0E+05 1.0E+06 1.5E+06 2.0E+06 2.5E+06 3.0E+06 **Z´ rel [**Ω**]**

=

parameters of the equivalent electric circuit are in table 2.

**Figure 21.** Z´´ versus Z´, for the 92Si samples treated at 650 ºC.

where Q0 and n are frequency independent parameters, but usually are temperature dependent. The parameter n varies between 0 and 1, when n = 1 the CPE is reduced to a capacitance element and when n =0 to a resistive element [18].The lines ("small dots") in the figures 21 to 23 represent the result of this adjustment. The values obtained for the

apparatus, in this frequency range.

represented by

0.0E+00

2.0E+07

4.0E+07

**Z´´rel [**

Ω**]**

6.0E+07

8.0E+07

1.0E+08

**Figure 19.** The dc conductivity (σdc, in logarithm scale) in function of 1000/T, for the 92Si samples treated at 700 ºC.

**Figure 20.** The dc conductivity (σdc, in logarithm scale) in function of 1000/T, for the 92Si samples treated at 700 ºC.

Figures 21 to 23 show the frequency dependence of the imaginary part of the impedance (Z´´) for the sample series treated at 650, 700 and 750 °C, respectively. It was observed, for the samples series treated at 650 and 700 °C, that Z'' decreases with the increase of frequency. In the frequency range used, the impedance (Z\*), the admittance (Y\*), the permittivity (ε\*) and the dielectric modulus (M\*) formalisms did not revealed the existence of dielectric relaxation(s). It must be noted that, for frequencies below 100 Hz, there is a high dispersion of the Z´´ values, which is associated with the sensitivity of the measuring apparatus, in this frequency range.

342 Heat Treatment – Conventional and Novel Applications

700

700B 700C

700A

treated at 700 ºC.





**ln(**σ**dc) [Sm-1]**




treated at 700 ºC.






**ln (**σ**dc) [Sm-1]**




**Figure 19.** The dc conductivity (σdc, in logarithm scale) in function of 1000/T, for the 92Si samples

2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 **1000/T [K-1]**

**Figure 20.** The dc conductivity (σdc, in logarithm scale) in function of 1000/T, for the 92Si samples

Figures 21 to 23 show the frequency dependence of the imaginary part of the impedance (Z´´) for the sample series treated at 650, 700 and 750 °C, respectively. It was observed, for

2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 **1000/T [K-1 ]**

750 750A

750B 750C An adjustment of the Z\* spectrum was carried out using a complex non-linear least squared deviations method (CNLLS) associated with the electrical equivalent circuit model formed by the parallel between a resistor (R) and a constant phase element (CPE). This constant phase element is characterized by keeping constant the angle of the impedance as a function of frequency, i.e. the ratio between the real and imaginary part of the impedance is constant across the all frequency range. The impedance of this intuitive element (ZCPE) can be represented by

$$Z\_{\rm CPE} = \frac{1}{Q\_0 \left(j\rho o\right)^n}$$

where Q0 and n are frequency independent parameters, but usually are temperature dependent. The parameter n varies between 0 and 1, when n = 1 the CPE is reduced to a capacitance element and when n =0 to a resistive element [18].The lines ("small dots") in the figures 21 to 23 represent the result of this adjustment. The values obtained for the parameters of the equivalent electric circuit are in table 2.

**Figure 21.** Z´´ versus Z´, for the 92Si samples treated at 650 ºC.

Lithium Niobiosilicate Glasses Thermally Treated 345

τ**Z (x10-3) [s]** 

**CCPE (x10-11) [F]** 

= ) and the value of the capacity nearest of the CPE

**n (x10-1)** 

with a field of 1000 kV/m) the largest value of R for all samples. The behavior of the Q0 parameter, in function of the thermal treatment conditions, is opposite to the observed for parameter R. In all samples, the value of the parameter n is very close to 1. Based on these calculated values a relaxation time, which represents the time average of the relaxation time

element value (Table 2). Evaluating the behavior of the parameter τZ (Table 2), with the increase of the electric field amplitude, it is verified that τZ increases with the increase of that amplitude in the sample series treated at 650 and 700 °C. In the samples treated at 750 °C, the increase of the amplitude of the external electrical field, induces an opposite behavior,

650 5,21 ± 0,18 6,13 ± 0,34 2,34 6,01 9,72 1,96 5,76 650ª 4,66 ± 0,12 1,81 ± 0,07 7,41 4,47 9,92 5,13 4,46 650B 4,82 ± 0,14 1,29 ± 0,06 23,90 4,54 9,94 20,94 4,54 650C 2,03 ± 0,07 1,61 ± 0,12 68,51 1,94 9,92 20,67 1,94 700 5,57 ± 0,20 2,79 ± 0,16 1,85 5,25 9,93 1,50 5,24 700ª 4,41 ± 0,16 2,39 ± 0,14 3,75 4,17 9,94 2,42 4,16 700B 4,50 ± 0,14 2,68 ± 0,13 4,59 4,41 9,90 3,10 4,38 700C 3,82 ± 0,11 2,92 ± 0,13 7,19 3,79 9,87 4,14 3,77 750 2,79 ± 0,09 8,40 ± 0,05 7,45 2,56 9,96 29,47 2,56 750ª 3,68 ± 0,19 2,03 ± 0,17 7,26 3,52 9,92 3,95 3,51 750B 6,07 ± 0,27 5,86 ± 0,40 4,26 6,91 9,73 4,26 6,69 750C 9,44 ± 0,28 21,20± 0,98 0,47 20,80 9,01 0,95 13,62

**Qo (x10-11) [**Ω**-1m-2sn]** 

max

**R (x108) [**Ω**]** 

**Table 2.** Dielectric constant (ε´) and dielectric loss (tan δ), at 1kHz and 300 K, parameters of the

The dependence of the dielectric constant (ε') with the frequency, at the temperature of 300 K, for the sample series of 650, 700 and 750 is represented in figures 24 to 26, respectively. It is observed that the value of ε' decreases with the increase of the frequency. Table 2 shows the values of ε', measured at 300 K and 1 kHz, for all samples. It can be verified that the increase of the amplitude of the external electrical field, for the samples treated at 650 and 700 °C, promotes a decrease of ε'. In the samples series treated at 750 °C, ε' increases from 2.8 to 9.4, with the increase of the amplitude of the applied external electric field. The CCPE capacitance behavior (Table 2), with the increase of the amplitude of the external electrical field, is similar to the one observed on the ε'. Table 2 contains also the values of the dielectric loss factor (tan δ = ε''/ε'), at room temperature

equivalent electric circuit (R, Q0 and n), relaxation time (τZ) and the CCPE capacitor.

1 / *<sup>Z</sup> <sup>Z</sup>*

 ω

τ

**(x10-2)** 

distribution, was calculated ( ´´

**Sample** ε**´ tan** <sup>δ</sup>

(300 K) and at the frequency of 1 kHz.

i.e., a decrease of τZ.

**Figure 22.** Z´´ versus Z´, for the 92Si samples treated at 700 ºC.

**Figure 23.** Z´´ versus Z´, for the 92Si samples treated at 750 ºC.

From the results obtained through the CNLLS fitting process, it is verified that the R parameter, of the samples treated at 650 and 700 °C increases, with the increase of the amplitude of the external electric field. In the sample series treated at 750 °C this parameter has the opposite behavior, i.e., it decreases with the increase of the applied electric field amplitude. However, it should be referred that the sample treated at 750 °C, but without the presence of an external electric field, shows the lowest value of R and the sample 750C (TTE with a field of 1000 kV/m) the largest value of R for all samples. The behavior of the Q0 parameter, in function of the thermal treatment conditions, is opposite to the observed for parameter R. In all samples, the value of the parameter n is very close to 1. Based on these calculated values a relaxation time, which represents the time average of the relaxation time distribution, was calculated ( ´´ max 1 / *<sup>Z</sup> <sup>Z</sup>* τ ω = ) and the value of the capacity nearest of the CPE element value (Table 2). Evaluating the behavior of the parameter τZ (Table 2), with the increase of the electric field amplitude, it is verified that τZ increases with the increase of that amplitude in the sample series treated at 650 and 700 °C. In the samples treated at 750 °C, the increase of the amplitude of the external electrical field, induces an opposite behavior, i.e., a decrease of τZ.

344 Heat Treatment – Conventional and Novel Applications

0.0E+00 5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+07 3.0E+07 3.5E+07 4.0E+07 4.5E+07 5.0E+07

0.0E+00 1.0E+07 2.0E+07 3.0E+07 4.0E+07 5.0E+07 6.0E+07 7.0E+07 8.0E+07 9.0E+07 1.0E+08

**Z´´rel [**Ω**]**

**Z´´ rel [**Ω**]**

**Figure 22.** Z´´ versus Z´, for the 92Si samples treated at 700 ºC.

**Figure 23.** Z´´ versus Z´, for the 92Si samples treated at 750 ºC.

From the results obtained through the CNLLS fitting process, it is verified that the R parameter, of the samples treated at 650 and 700 °C increases, with the increase of the amplitude of the external electric field. In the sample series treated at 750 °C this parameter has the opposite behavior, i.e., it decreases with the increase of the applied electric field amplitude. However, it should be referred that the sample treated at 750 °C, but without the presence of an external electric field, shows the lowest value of R and the sample 750C (TTE

0.0E+00 5.0E+05 1.0E+06 1.5E+06 2.0E+06 2.5E+06 3.0E+06 3.5E+06 4.0E+06 4.5E+06 5.0E+06 **Z´rel [**Ω**]**

0.0E+00 1.0E+06 2.0E+06 3.0E+06 4.0E+06 5.0E+06 6.0E+06 **Z´rel [**Ω**]**

**750**

**700**

**750A**

**750B**

**750C**

**700A**

**700C 700B**


**Table 2.** Dielectric constant (ε´) and dielectric loss (tan δ), at 1kHz and 300 K, parameters of the equivalent electric circuit (R, Q0 and n), relaxation time (τZ) and the CCPE capacitor.

The dependence of the dielectric constant (ε') with the frequency, at the temperature of 300 K, for the sample series of 650, 700 and 750 is represented in figures 24 to 26, respectively. It is observed that the value of ε' decreases with the increase of the frequency. Table 2 shows the values of ε', measured at 300 K and 1 kHz, for all samples. It can be verified that the increase of the amplitude of the external electrical field, for the samples treated at 650 and 700 °C, promotes a decrease of ε'. In the samples series treated at 750 °C, ε' increases from 2.8 to 9.4, with the increase of the amplitude of the applied external electric field. The CCPE capacitance behavior (Table 2), with the increase of the amplitude of the external electrical field, is similar to the one observed on the ε'. Table 2 contains also the values of the dielectric loss factor (tan δ = ε''/ε'), at room temperature (300 K) and at the frequency of 1 kHz.

Lithium Niobiosilicate Glasses Thermally Treated 347

**Figure 26.** ε´ versus frequency, at 300 K, for the 92Si samples treated at 750 ºC.

Figure 27 shows the macroscopic aspect of the 88Si sample composition, TT at 500, 600, 650, 700 and 800 ºC, during 4 hours. It can be seen that the as-prepared glass (TT at 500 ºC) is

**Figure 27.** Photographs of the 88 Si samples TT at temperatures between 500 and 800 ºC (the minor

As-prepared TT600 TT650 TT700 TT800

Figure 28 shows the XRD patterns of the samples TT. This spectrum shows the presence of LiNbO3 crystalline phases and cristobalite (SiO2), in the samples treated at temperatures above 650 °C. With the increase of the TT temperature up to 700 °C it was detected also the lithium silicate (Li2Si2O5) crystalline phase. In order to confirm the indexing of some diffraction peaks observed in the sample TT at 800 °C, the XRD was carried out in a new sample, TT at 800 °C but during 8h (sample 800-8h). Analyzing the pattern of this sample it is suggested the presence, in the samples treated at 800 °C, of the Li3NbO4 crystalline

**8. 88Si samples composition results** 

scale division = 1mm).

phase.

translucent and for TT above 700 ºC it becomes opaque.

**Figure 24.** ε´ versus frequency, at 300 K, for the 92Si samples treated at 650 ºC.

**Figure 25.** ε´ versus frequency, at 300 K, for the 92Si samples treated at 700 ºC.

**Figure 26.** ε´ versus frequency, at 300 K, for the 92Si samples treated at 750 ºC.
