New heavy-metal fluoride glasses in ZrF4FeF3PbF2YF3 systems

64

Journal of Non-Crystalline Solids 109 (1989) 64-68 North-Holland, Amsterdam

NEW HEAVY-METAL F L U O R I D E G L A S S E S IN ZrF4-FeF3-PbF2-YF3 S Y S T E M S H A N Jianfeng Shanghai Electric Cable Research Institute, 1000 Jungong Road, Shanghai 200093, P. R. China

C H E N G Ji-Jian Department of Inorganic Materials, East China University of Chemical Technology, 130 Meilong Road, Shanghai 200237, P. R. China

Received 17 August 1988 Revised manuscript received 13 December 1988

A new family of fluoride glasses has been found in the ZrF4-FeF3-PbF 2 ternary and ZrFa-FeF3-PbF2-YF 3 quaternary systems. These glasses have a wide range of transparency spanning the 0.6-8 ttm region, and refractive indices between 1.64-1.67. The electrical conductivities of the glasses can exceed 8.0 × 10 -6 ~-1 cm - |. The glasses also exhibit attractive magnetic characteristics, including spin-glass behaviour and magneto-optic rotation. The discussion of the structure of the glasses is based on spectroscopicinvestigations.

1. Introduction

2. Experimental procedures

Since their discovery in 1975 [1], heavy-metal fluoride glasses have attracted considerable interest as candidate materials for ultralow loss optical components and fibres in the visible to mid-infrared region. They also offer potential as laser hosts, magneto-optic devices, electroluminescence panels, etc. [2-4] when 3d transition metal or rare earths are present. Miranday et al. have prepared a family of fluoride glasses with a high transition metal fluoride content [5]. The properties and structural investigations of these glasses were also reported [6,7], but additional studies in this field are limited. The above results led us to develop a new kind of mixed fluorozirconate-TM (transition metal) based fluoride glass. The addition of zirconium tetrafluoride, a better glass former, to TM fluoride glasses may improve the glass forming ability, allow the preparation of the samples a few m m thick and provide a larger vitreous domain. In addition, glass properties are also expected to change.

The starting raw materials PbF 2, ZrO 2, Fe203, Y203, and A1F3 were obtained from a commercial source and mixed completely with an excess of N H 4 F - H F to convert oxide species to fluorides. The batches were melted in covered platinum crucibles under reactive atmospheres (CCI 4 + N2) in a resistance-heated furnace. Melting was done for 4 to 6 h at the maximum temperature of 680 to 850 ° C, depending on the composition. The glass melts were poured between two brass blocks (preheated at 210-230 ° C) and then annealed near the glass transition temperature. The sample thickness was from 0.5 to 4 ram, and some stable samples could be cut in pieces of 30 × 15 × 2 mm 3 as well. The color of glasses changes from a greenish yellow to a reddish brown as the FeF 3 content increases. Glass transition and crystallization temperatures were taken from differential thermal analysis (DTA) traces at a heating rate of 10 ° C / m i n . The optical measurements were recorded in the UV-visible (0.2-2.5 /~m) region utilizing a

0022-3093/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

Han Jianfeng, ChengJi-Jian / New heavy-metalfluoride glasses

65

z~

Shimadzu UV-365 double-beam spectrometer and in the infrared region (2.5-25 t~m) with a Nicolet FT-IR 20SX spectrophotometer. Determinations of the refractive index, density, and electrical conductivity of the glasses were made using the standard methods. The DC magnetization of such glasses was carried out with the extraction method in a pumped liquid helium bath, and the instrument has a superconducting magnet whose field strength is up to 70 kOe. The magneto-optic rotation (Faraday effect) of the glass was measured by the magneto-optic rotation instrument at Jiaotong University in Shanghai.

FeF~

2O

40

6O

8O

PbF2

Fig. 1. Glass-forming region in the Z r F 4 - F e F 3 - P b ~ ternary. system.

vitreous area increased with respect to the original system. In this case, samples of 3 - 4 mm in thickness could be obtained. When YF 3 reached 8 mol% or greater, however, the glasses devitrified.

3. Results and discussion

3.1. Glass-forming systems 3.2. Physical properties The glass-forming region in the system ZrF 4FeF3-PbF 2 is shown in fig. 1. Glass could also be obtained in the binary system PbF2-FeF 3 corresponding to the previous report [5]. The limits of the vitreous domain in this ternary system are dependent on the quenching rate. Because of their tendency to crystallization upon cooling of melt, the maximum thickness of the ternary system glasses is about 1 - 2 mm, so they were not annealed. In order to get large samples, a fourth component was introduced, which led to quaternary glasses. Lanthanide group elements have always been used as a fluoride glass stablizer. As shown in fig. 2, we added 2 mol%, 4 mol%, and 6 mol% YFa to the ternary system, with the result that the

Glass transition temperature (Tg) and onset of crystallization (Tx) have been determined by DTA and some are listed in table 1. Tg was found to vary between 230 to 270 o C, and T× between 270 to 340°C, lower than that observed for fluorozirconate glasses (e.g. ZBLA, 57ZrF4-34BaF2-5 LaF3-4A1F3: Tg= 320°C, Tx = 392°C [8]), but comparable to the values for transition metal fluoride glasses (e.g. PMF, 35PbF2-20MnF2-45FeF3: Tg= 299°C, Tx = 3 1 7 ° C [5]). The lower Tg may be the result of PbF 2 incorporation. The difference Tx - Tg has frequently been used as a rough indicator of glass-forming ability. Since the Tx-T~ values seem to increase with FeF 3 content, it suggests that incorporation of FeF 3 favours

Table 1 Glass compositions and selected properties Glass No. 1 2 3 4 5 6 7

Batch composition (mol%) ZrF 4

FeF~

PbF2

20 10 100 5 28 32

44 30 40 55 37 18 13

56 50 50 35 52 46 46

YF 3

A1F3

Tg ( ° C)

Tx - Tg ( ° C)

Density ( g / c m 3)

r/D

245 244 244 248 255 250 244

35 47 56 62 53 70 72

6.11 5.86 5.95

1.670 1.650 1.645

66

Han Jianfeng, Cheng Ji-Jian

/ New heavy-metal fluoride glasses

z,.F4

z,.F~

20~80

2mot%YF3

20 / ~ k X 8 0

4moI Z yF5

%

80/, ,{/,
20

40

60

80

PbF2

FeF3

20

60

40

zos4

80

PbF2

z~F4

2o~8o

6~o,

%Y~3

2o//k'k 80

oo/

?j,
2O

.~0

60

80

PbF2

7 , , :," F~F~

20

40

60

80

PbE2

Fig. 2. Glass-forming regions in the ZrF4-FeF3-PbF2-YF3 quaternary system at 2, 4, 6, and 8 mol% YF3.

/00

glass formation and that F e F 3 p r o b a b l y plays the role of glass former. Although Tg does not increase with Y F 3 additions, the glass-forming ability was experimentally observed to improve and the sizes of vitreous areas were enlarged. In addition, introduction of 2 - 3 mol% A1F3 to the quaternary glasses enhanced Tx - T ~ , and large h o m o g e n e o u s samples were fabricated as well, as reported earlier [8].

7O

0

i

50O

3.3. Optical properties

The range of refractive indices obtained with compositional variation is 1.64 to 1.67, which is higher than fluorozirconate glasses (e.g. Z B L A , n D = 1.519 [8]) (Table 1). It is reasonable to expect that the higher refractive indices for these glasses result from the large molar refractivities of heavier cations (Pb 2÷, Zr4+), as described by Goldstein and Sun [9]. Typical visible and infrared transmission curves for the 1 9 Z r F a - 2 3 F e F a - 5 2 P b F 2 - 6 Y F 3 glass are shown in figs. 3 and 4, which were taken on a polished sample 2 m m thick. The absorption bands around 650 and 1050 n m can be assigned to transition 6 A I ~ ( 6 S ) - 4 T l g ( 4 G ) for Fe 3+ a n d

/

35

f

I000

I

1500 2000 2500 Wavelengfh (am)

Fig. 3. Percent transmission vs. wavelength (0.4 to 2.5 #m) for glass (mol%) 19ZrF4-23FeF 3-52PbF2-6YF3, sample thickness 2.0 mm. /00

o.~35 t

4000

JlO0

I

2200

1300 400 l,/evenurnbers (cm-'l

Fig. 4. Percent transmission vs. wavenumber (4000 to 400 cm-l) for the same glass as in fig. 3.

Han Jianfeng~ ChengJi-Jian / New heavy-metalfluoride glasses

67

Table 2 Electrical conductivity o and activation energy E . for some glasses Glass

Batch composition (mol%)

No. 1 2 3 4 5 6

ZrF 4

FeF 3

PbF 2

YF3

A1F3

32 27 18 28 28 32

13 18 27 18 19 14

46 46 46 46 46 46

6 6 6 6 6 6

3 3 3 2 1 2

STzg(D)_ 5Eg(D) for Fe 2

respectively. The transmission in the glass extends to 8/~m. +

mid-IR

o at 200 o C ( 0 -1 cm 1)x10-6

Ea (eV)

7.37 5.82 1.94 6,28 7.38 8.07

0.78 0.80 0.90 0.80 0.72 0.67

O.l H=420e

3.4. Electrical and magnetic properties The electrical conductivities at 2 0 0 ° C and activation energies for some glasses are given in table 2. Figure 5 shows the o vs 1 / T plot for these glasses. In the temperature range of study (from 80 to 200 ° C), the electrical conductivities obey an Arrhenius equation:

005 • %o ".

% •-

o • ..:

o %

..o•

~

o ~

©o

•

o = o 0 e x p ( - R ~ ),

0

(1)

.

l

.

o .

•

.

o

•

o

.

,

I0

20

30

40 T fK)

where E a is the activation energy for electrical conduction. We can see that the electrical conductivities increase gradually with substitution of Fe 3+ by Z r 4+ from table 2. It is likely that Z r 4+, usually

Fig. 6. The DC magnetization vs. temperature M(T) for two glasses: No. 3, 18ZrF 4 - 2 7 F e F 3 - 4 6 P b F 2 - 6 Y F 3 -3A1F 3, and No. 6, 32ZrF4 - 1 4 F e F 3 - 4 6 P b F 2 - 6 Y F 3 -2A1F 3 in a field of 42 Oe.

15

7

:

:

/

:

:

2

T=I.SK a ......

<)---o-4 t>-o- 5

/o

-6 0

0 B

0

0 o

0

0

0

I

0

fl

-7 g g g

-8 g

I

2.0

2.5

I

3.5

i

0 --~ K-9

Fig. 5. Arrhenius plots of the electrical conductivities for some glasses. Glass compositions are listed in table 2.

/0

.

i

20

.

i

JO

,

~

40

i

L

50

60

70

H (KOe)

Fig. 7. The field-dependent curves of the magnetization M ( H ) at 1.5 K for glasses Nos. 3 and 6.

68

Han Jianfeng Cheng Ji-Jian / New heavy-metal fluoride glasses

coordinated by 6 - 8 fluorines, allows more nonbridging fluorine (NBF) to exist than Fe 3÷ does, whereas the fluorine transport in H M F glasses takes place through the displacement of N B F ions [10]. In addition, A13+ ions, as the network stabilizer, are thought to occupy an octahedral site and play the role of intermediate [8]. The mobility of N B F ions is therefore restrained by the electrostatic interaction between A13+ ions and F - ions, so adding A1F3 to these glasses decreases the electrical conductivity (table 2). The variation of D C magnetization vs. temperature M(T) for glasses No. 3 and No. 6 (table 2) in a field of 42 Oe is indicated by fig. 6. It appears that the M(T) curves decreases very rapidly near 6 to 10 K, which is probably due to the spin-glass behaviour of these glasses, as observed in amorphous NdxT l_x (T = Fe, Co, Ni) thin films [11]. There is a need for further study of this property. The field-dependent curves of the magnetization M(H) for the above glasses at 1.5 K are presented in fig. 7. The magnetization of such glasses initially rises steeply with increasing magnetic field, but is completely saturated up to 60 kOe. The magneto-optic effect (Faraday rotation) for the sample 37ZrF4-5FeF3-52PbF2-6YF 3 was determined by a magneto-optic rotation instrument. The Verdet constant is 0.029 m i n / O e - c m at 6328 A.

3.5. Structure The glass structure was intensively investigated by XRD, ESR, N M R , M~Sssbauer, I R and R a m a n spectroscopies [12]. The results indicated that the

(FeFr) octahedra and (ZrF~) polyhedra (n = 6-8, mainly 7), as the basic network formers of the glass, are randomly linked by corners a n d / o r edges to form a disordered three-dimensional network, whereas PbF 2 and Y F 3 play the role of network modifier and stabilizer, respectively.

4. Conclusion New heavy-metal fluoride glasses were obtained in Z r F 4 - F e F 3 - P b F 2 ternary and ZrF4-FeF 3 - P b F 2 - Y F 3 quaternary systems. Physical, optical, electrical and magnetic properties measurements for these glasses indicate a wide infrared transparency, high refractive index and electrical conductivity, and attractive magnetic properties.

References [1] M. Poulain, M. Poulain and J. Lucas, Mat. Res. Bull. 10 (1975) 243. [2] J.P. Renard, J.P. Miranday and F. Varret, S.S. Comm. 35 (1980) 41. [3] W.A. Sibley, Mat. Sci. Forum 5 (1985) 611. [4] J. Lucas, J. Less-Common Metals 112 (1985) 27. [5] J. Miranday, C. Jacoboni and R. de Pape, J. Non-Cryst. Solids 43 (1981) 393. [6] C. Jacoboni, A. Le Bail and R. de Pape, Glass Teclmol. 24 (1983) 164. [7] A. Le Bail, C. Jacoboni and R. de Pape, Mat. Sci. Forum 5 (1985) 441. [8] A. Lecoq and M. Poulain, Verres Rrfract. 34 (1980) 333. [9] N.P. Goldstein and K.H. Sun, Bull. Am. Cerarn. Soc. 58 (1979) 1182. [10] D. Ravaine, Mat. Sci. Forum 5 (1985) 761. [11] Dai Bao-sheng et al., Acta Phys. Sinica 35 (1986) 476. [12] Han Jianfeng and Cheng Ji-Jian, Paper NF6, 1988 Shanghai Int. Symp. on Glass, J. Non-Cryst. Solids, to be published.