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t THERMAL AND DIELECTRIC PROPERTIES OF BOROSILICATE

GLASSES – EFFECT OF B2O3/SiO2 RATIO

A.A.S.LOPES1; R.C.C.MONTEIRO1; C.J.DIAS1; L.F.R.DAVIM2; E.J.R.DAVIM2 and M.H.V.FERNANDES2

1Departamento de Ciência de Materiais, CENIMAT/I3N, Faculdade de Ciências e Tecnologia,

Universidade Nova de Lisboa, 2829-516 Caparica 2Departamento de Engenharia de Materias e Cerâmica & CICECO, Universidade de Aveiro, 3810-193 Aveiro

Borosilicate glasses, due to their low softening temperature, low thermal

expansion and low dielectric constant, have been considered promising

materials for different electronic industrial applications. These materials

contain usually PbO, a glass network modifier with adverse health and

environmental effects during processing, forcing the search for safer

alternatives. Recently, BaO and ZnO have been used as potential

candidates that can replace PbO.

Two series of glasses based on BaO-ZnO-B2O3-SiO2 system were

developed, where the amount of SiO2 was fixed at 10 mol%, the amount of

B2O3 was 30 or 60 mol% (B30 or B60), and the network modifier ZnO was

gradually substituted by BaO. Bulk transparent glasses were obtained by

the conventional melting route, casting and annealing steps. The goal of

this study is to evaluate the effect of compositional changes on the thermal

and dielectric properties.

BaO-ZnO-B2O3-SiO2

DTA

Density (Archimedes method, Helium pycnometer)

Melting Temperature

(Tf = 1100 / 1450 ºC, t = 1h)

Glass bars

Dilatometry

XRD

Characterization

Permittivity and dielectric loss

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Glassy

Crystalline

ZnO

B2O

3 + SiO

2

BaO

0 10 20 30 40 506

9

12

15

18

Theoretical value (B60)

1MHz (B30)

1MHz (B60)

Die

lectr

ic c

onst

ant

(r)

BaO content (mol%)

Theoretical value (B30)

10 20 30 40 50 60 70

B30 Ba 0

B30 Ba 20

B30 Ba 10

B30 Ba 30

B30 Ba 40

B30 Ba 50

2 (degree)

B30 Ba 60

10 20 30 40 50 60 70

B60 Ba 0

2 (degree)

B60 Ba 10

B60 Ba 20

B60 Ba 30

endo

400 450 500 550 600 650 700 750

B30 Ba

B30 Ba10

B30 Ba20

B30 Ba30

B30 Ba40

B30 Ba50

Temperature (ºC)

B30 Ba60

exo

endo

400 450 500 550 600 650 700 750

B60 Ba

B60 Ba10

B60 Ba20

B60 Ba30

Temperature (ºC)

exo

XRD patterns for the 2 series of glasses

Glass compositions (mol %) (Symbol size according to permittivity value)

Coefficient of thermal expansion (CTE) of each specimen as a function of BaO content

Dielectric constant and dielectric loss as a function of BaO content

0 10 20 30 40 50 600

5

10

15

20

25

30

35

40

45

Experimental value

CTE (

x10

-6/ºC

)

BaO content (mol %)

Theoretical value

B30

0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

45 B60

Experimental value

CTE (

x10

-6/ºC

)

BaO content (mol %)

Theoretical value

0 10 20 30 40 501E-3

0.01

0.1

Die

lectr

ic loss

BaO content (mol%)

1MHz (B30)

1MHz (B60)

• For a fixed BaO content, the glass transition, softening and glass crystallization temperatures increase with the B2O3/SiO2 ratio.

• Increasing the BaO content in series B30 decreases the glass transition, softening and glass crystallization temperatures, whereas the opposite effect is

observed in B60 series. The non-linear behaviour of the glass characteristic temperatures between the two glass series is interpreted in terms of boron

anomaly phenomenon, i.e, BO4 tetrahedra transform into BO3 groups in B30 and the opposite occurs in B60 series.

• Increasing the BaO content increases the CTE and the dielectric constant whereas increasing B2O3/SiO2 ratio decreases both CTE and dielectric constant.

These results show that Ba ions have a stronger effect on the glass network disruption and decrease of rigidity compared to Zn ions.

This work was performed in the scope of Project PTDC/CTM/102141/2008 financed by FCT-MEC

DTA curves for the 2 series of glasses Change of glass transition temperature (Tg), softening temperature (Tsp) and

crystallization temperature (Tc) with BaO content for the 2 series of glasses

0 5 10 15 20 25 30510

540

570

600

630

660

690

720

750

Tg

Tsp

Tem

pera

ture

(ºC

)

Ba0 content (mol%)

B60

Tc

0 10 20 30 40 50450

480

510

540

570

600

630

660

690

Ba0 content (mol%)

Tem

pera

ture

(ºC

)

B30

Tc

Tsp

Tg