JOURNAL OF NON-CRYSTALLINESOLIDS 11 (1972) 121--130 © North-Holland Publishing Co.

G L A S S F O R M A T I O N A N D D.S.C. D A T A IN T H E
Ge-Te AND As-Te MEMORY GLASS SYSTEMS

J. A. SAVAGE
Royal Radar Establishment, Great Malvern, Worcestershire WR14 3PS,
England

Received 21 February 1972; revised manuscript received 7 April 1972
The glass forming regions for 2.0 g liquid nitrogen quenched melts in the Ge-Te and As-Te systems are reported, together with glass transition temperatures, metastable melt crystallization temperatures and calorimetric data for glass powder heated at 5 °C/min in an argon atmosphere under standardised conditions. Various elemental additions such as B, AI, Si,
P, S, Ga, As, Se, In, I and TI have been substituted for Te in the basic Ge15Tes~eutectic and a possible role of these minor additions in prolonging device lifetime is discussed. The element aluminium has been found to have a beneficial effect on glass formation in telluride systems and a new glass forming region, AI-As-Te, is separately reported in the appendix.

I. Introduction
It has been shown that m e m o r y switching devices can be made from glasses in the G e - A s - T e system and that these devices are of potential use for m a n y applications such as in the control of electroluminescent display panels 1) and in read only memories 2). The glass forming region and a D.T.A. survey in this system has been previously reported 3). In the present work binary glasses in the G e - T e and A s - T e systems and some ternary glasses have been examined by D.S.C. and X-ray diffraction techniques in an attempt to establish a rapid means o f identifying potential device quality m e m o r y compositions which would be worthy of a full investigation.

2. Experimental procedures
2.1. GLASS PREPARATION
Two gram quantities o f glass were prepared from J o h n s o n and Matthey spectrographically standardised elements in evacuated, sealed silica tubes as previously described 3). The sealed tubes were heated to a temperature of
850 °C in a rocking furnace and rocked at this temperature for 5 hr, then removed from the furnace and quenched in liquid nitrogen. The quenched melts
121

122

J .A .SAVAGE

were assessed as vitreous or crystalline by evidence of conchoidal

fracture,

glass transition and X-ray diffraction.
2.2 D.S.C.

CALIBRATION AND MEASUREMENT TECHNIQUE

A Du Pont 900 thermal m e t e r cell w e r e e m p l o y e d in the range

20°C/min

in this work. It was calibrated

150°C to 420°C

2.5 °C of their published determinations analyser console and differential scanning calori-

were

on 50 mg

and the melting

points

with metals melting were obtained

within

v a l u e s . I n a n i n i t i a l s u r v e y o f all t h e g l a s s e s , D . S . C .

made

in an

of quenched

argon

atmosphere

pieces of bulk

s c r i b e d 3). M o r e d e t a i l e d D . S . C . i n f o r m a t i o n

at a heating

glass

as

rate

previously

was obtained on powdered

samples. In this technique the quenched glass was powdered

of de- glass

in an agate mortar

in an argon glove box, sieved to a 240 mesh particle size and then placed in

TABLE 1
D a t a obtained on powdered q u e n c h e d glasses heated at 5 ° C / m i n
Glass
composition

Tg

(at ~ )

(°C)

Tx M a i n peaks (°C)
(°C)

Tx Satellite peaks (°C)
(°C)

GelsTea5
Ge~0Te8o
CrelsTeslA14
Gel~TeslSb~S2
Ge15Teslln4
GelsTeslB4
Gel~Tes~P4
GelsTaslGa4
GelsTes1As4
Ge15Te8114
Ge15TealTI4

121
146
136
123
132
121
124
134
125
117
106

184
205
202
196
199
184
192
202
195
173
163

207
214
227
220
212
212
184

283
232
268
272
-

As25Te75
As4~Te55
AssoTeso
As~sTe4~
As6oTeao
As6~Te85
AszTe3
AszTe3
(literature)
As20Te75Ge5
As5oTeasGe5

82
119
128
139
150
140
.

132
181
207
236
240
242
.

235
-

230