Certain Physical Properties of Single Crystals of

Certain Physical Properties of Single Crystals of Tungsten, Antimony, Bismuth, Tellurium, Cadmium, Zinc, and Tin Author(s): P. W. Bridgman Source: Proceedings of the American Academy of Arts and Sciences, Vol. 60, No. 6 (Oct., 1925), pp. 305-383 Published by: American Academy of Arts & Sciences Stable URL: http://www.jstor.org/stable/25130058 . Accessed: 18/06/2013 13:35 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp

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CERTAIN PHYSICAL PROPERTIES OF SINGLE CRYSTALS OF TUNGSTEN, ANTIMONY, BISMUTH, TELLURIUM, CADMIUM, By Received

November

ZINC,

P. W.

TIN.

AND

Bridgman.

6, 1924.

Presented

8, 1924.

October

TABLE OF CONTENTS. 305 Introduction. of Growing Method 307 Large Single Crystals. of Measurement Methods and Computation. 315 Thermal 315 Expansion. . 316 Electrical Resistance . .. Elastic Constants 323 of Measuring Methods Strain. Experimental Detailed 329 Data. 329 Tungsten. Zinc. . Thermal Expansion Electrical 335 Resistance. Elastic 338 Constants. 342 Cadmium.,. Thermal 343 Expansion. Electrical 343 Resistance. , 345 Elastic Constants. of Cadmium under Pressure Transitions . . . .. Bismuth Thermal 351 Expansion. Electrical 351 Resistance. Elastic 355 Constants. ....... Antimony Thermal Expansion. Electrical Resistance. Elastic Constants 366 Tellurium. Thermal Expansion Electrical Resistance. Elastic Constants. Tin. Thermal Expansion. Electrical Resistance. Elastic Constants. 380 Magnetic Properties. and General Summary Survey

327

333 .

...

334

.... ...

.

346 349

358

358 359 ,.

364

...

.

367

368 369 371 373 373 377 of Results.

380

Introduction.

The importance of a knowledge of the physical properties of single crystals of the metals requires no argument. Very little is known of the subject, however. Until within a few years, practically all that we had was a determination of the three elastic constants of a natural


BRIDGMAN.

306

of

crystal ductivity

of and copper, at low temperatures,

electrical

its

and

and

resistance

questionable

con

thermal on

data

the

thermal

the metal expansion and electrical properties of bismuth. Recently of single crystals particularly lurgists have studied the properties with regard to plastic flow when stressed beyond the elastic limit, in order to better understand the behavior of crystalline aggregates when

stressed

the

beyond and

zinc,

aluminum, this present

tin.1

was

of flow

a year,

now

thermal

constants,

rather

of

a good of part have and Goens2

after

and

a

have

in single crystals

Gruneisen

completed,

elastic

we

and

limit,

Within

investigation for data the

published

elastic

of the phenomena

knowledge

complete

and

expansion,

resistance of single crystals of zinc and cadmium. With the exception of the single crystal of copper, this seems to be the first electrical

knowledge

of

tinguished

from

the

detailed

the

constants

elastic constants

average

by

given

of

any

an

isotropic

as

metal,

dis

aggregate.

Several years previously I had found very great differences of the linear compressibility of a number of metals in different directions, but had not sufficient data for the detailed constants.3 The need of a detailed study of the properties of single crystals is greatest in those metals which do not crystallize in the cubic system, because

of

many

the

of a cubic

properties

are

crystal

same

the

in all

directions, and therefore will be the same for a single crystal as for an isotropic agregate, of which we already have sufficient knowledge. are properties electrical resistance, are required constants such

Among pansion, elastic for

the

non-cubic

for

the

Three

however,

crystal,

ex

thermal

compressibility, thermal conductivity.

studied particularly

metals, I was

because

antimony,

namely

and

cadmium

(trigonal), Also,

linear and

two

against

aggregate.

In this paper I have able

the

zinc,

fortunate

the more

readily obtain

bismuth,

and

to

enough

tin

and

(hexagonal),

a fine

obtain

tellurium,

(tetragonal). crystal

single

The proper of tungsten, I have determined certain of its properties. ties of these metals which I have examined are as follows. (1) Ther mal

In

Expansion.

constants are four-,

or

six-fold

give

symmetry,

right angles to such an axis. measuring

the

linear

a

small

range

of

the and

along in

on

rods

cut

These

expansion. an

axis

every

of

three-, at

direction

easily be determined along

determined both

two

tungsten,

except

expansion the expansion

of

expansion

temperature

above,

the thermal

They may most

expansion

The

these directions.

cases

the

to determine

which

constants

the

of

all

are sufficient

sides

one

or

the

in the following of

room


by

other

of

is for

temperature.

PHYSICAL

(2) Electrical stants

like

of

those be

also

may

The

Resistance.

are

sistance

PROPERTIES

OF

symmetry

thermal

determined

by

resistance

for

resistance

between

the

necessary 0? and

are

more

much The

sistance.

re

the

requisite

con

on

samples

lying

I have determined

the specific

coefficient the temperature a function of direction, and

directions, C. as

100?

of the

pressures up to 12000 kg/cm2 between 0? and in different directions. (3) Elastic Constants.

effect of hydrostatic 100? C. on resistance These

and

307

of electrical

relations

expansion, measurements

along the axis or at right angles to it.

ETC.

TUNGSTEN,

complicated have metals

trigonal

than six

thermal

expansion the tetragonal

constants,

or

re six,

I have determined and the hexagonal five. these constants by of the elastic deformation of properly oriented speci measurements the linear compressibility in mens, and have in addition measured two directions to 12000 kg., which gives information about the be havior

under

of certain

pressure

of the

combinations

elastic

constants,

It is sufficient to and in particular gives the cubic compressibility. as is the measure in only two directions, the linear compressibility case

for

and

resistance

thermal

expansion.

the measurement of difficulty which has prevented of metals in the doubtless that of is past crystal properties preparing single crystals of sufficient size. In this paper I first describe in detail the method by which the specimens were prepared (I have method sketched in general outline2), then the general this already The

chief

of making

methods

data

detailed

Method

The A

various

the

of

Growing

general method

tubular

sorts

of measurements,

and

then

the

for the individual metals.

electric

furnace,

Large

Single

Crystals.

is that of slow solidification in a vertical

position,

from the melt.

is maintained

at

a

The temperature above the melting point of the metal in question. metal in the molten condition in a suitable mold of glass or quartz tubing is slowly lowered through the bottom of the furnace into the air of the room or into a cooling bath of oil. Solidification thus starts at the bottom of the tube and proceeds slowly along its axis, keeping If the lowering is at a speed less than the pace with the lowering. of crystallization and also slow enough so that the latent velocity heat of solidification may be dissipated by conduction, then the metal will usually crystallize as one grain, provided that only one nucleus started in the tube at the bottom. The final casting has of course the cylindrical shape of the mold, not the geometrical form characteristic of the crystalline system of the metal.


BRIDGMAN.

308

It is, possibly, surprising that this method works for all of the metals of the list, because several of them are known to have polymorphic transitions between the melting point and room temperature (tin and antimony). It is evident that on passing through a transition point the same process repeats itself that took place at the melting point.

In applying this method in practise there are various details to attend to. The most difficult and important is to secure the formation of only one grain at the bottom end. This is not always absolutely in much

and

necessary,

of my

early

work

no

I took

special

precautions

in this direction and obtained suitable single crystals after cutting off The reason is that one orientation the bottom ends of the castings. of the grains is usually much more favorable for growth than others, so that even if a number of grains start at the bottom, that grain will The most eventually win through which ismost favorably situated. is in almost all cases with the plane of easiest favorable orientation _1*

_

?

c=xT Figure

1.

The

A

X

mold

in producing

used

large

single

r^ crystals.

This does not fix cleavage or slip parallel to the axis of the casting. the orientation of the grain uniquely, since this plane of cleavage may have

orientation

any

within

180?

about

axis

the

of

the

so

casting,

that a number of grains may start all equally well situated for growth; the entire length of the these grains will then persist throughout casting. one must ensure

To

ensure, therefore, on something depend the formation of only

of schemes with varying of

the

out

mold

into

a

a reasonably high more positive one

success. separate

original

percentage than mere I

grain.

tried

of success, to

chance a

number

The best is to draw the lower part chamber,

separated

from

the

main

part by a capillary 0.1 mm. or so in diameter, as shown in Figure 1. The capillary acts as a filter, allowing only one of the several grains which may have formed initially in the lower bulb to get through into the main part of the mold. Even this will not always ensure success, because if the grain which gets through the filter is particularly un favorably situated for growth, a more favorably oriented grain is likely avoid

to make this

chamber

its appearance as much

occurrence

fairly

long, so that

spontaneously as possible,

the formation

at

some

later

one

may

make

of the most


stage. the

To lower

favorably

physical

situated

grain

of

properties

as much

have

may

as

chance

below the filter instead of above it. After the proper starting of the crystal, to prevent

taken are

the

easy.

comparatively

of new

appearance The

most

etc.

tungsten,

309

to

possible

must

precautions but

nuclei,

these

place

still be

precautions from dirt.

is freedom

important

take

Specks of dirt clinging to the side of the glass are likely to start new The most likely dirt is small particles of oxide; it is practically grains. impossible to melt a piece of metal which has once solidified and come in contact

with

the

the

air without

of

appearance

of oxide,

specks

even

if the melting is performed in vacuum. metal clean, I usually melted the metal

In order to obtain the molten in an ante-chamber before the

mold

by

proper,

from

separated

the mold

a narrow

capillary,

which

acts as a filter to remove solid dirt. Figure 1 will suggest the general method of procedure. The metal in sufficient quantity is first placed in the ante-chamber A through the open mouth of the mold, which is then drawn down at the top end B and a glass tube attached by which The mold connections may be made with rubber tubing to vacuum. is now placed in the furnace, the chamber A projecting beyond the is evacuated upper end of the furnace; the mold through B by a oil with it in which remains pump connection, and the furnace rotary is brought to temperature. The furnace with the mold in it is then brought to a horizontal position by rotating about a suitable axis on so that now the ante-chamber with the unmelted which it ismounted, metal projects in a horizontal position from the furnace. The metal is now

melted

by

an

auxiliary

gas

flame,

and

raised

to a temperature

somewhat above that of the furnace. By tipping the furnace, the metal iswashed back and forth in A. This is an important operation, because

which casting.

in this way

otherwise Some

large

quantides

separate during metals

are

much

of occluded

be

gas may

eliminated,

solidification

and give an imperfect

worse

others

than

in

this

respect;

bismuth particularly is bad, and it may be necessary to manipulate the molten metal for an hour or more before all the gas bubbles have After getting rid of the gas, the furnace is rotated back disappeared. to the vertical position, and the metal allowed to filter through into to hasten the filtering. the mold, admitting air to the antechamber It is well to choose such a quantity of metal that it finally stands a little above the passage from A to C, thus keeping any oxide on the The glass tube at B is sealed upper surface and out of the final mold. Solidi off, to prevent further access of air and continued oxidation. fication is now started by lowering the mold. In addition to the complete removal of dirt, the chance formation


BRIDGMAN.

310

of new grains is hindered by a proper design of the mold; a too obtuse start new grains, probably taper above the lower capillary may because

the

does

temperature

not

change

at

uniformly

a

such

taper.

The proper speed of lowering depends very much on the metal and to this the size of the mold. In general, the speeds appropriate method are very much less than those used in drawing wires out of the of

surface the

walls

glass

librium.

as would be expected metal, in restraining the attainment as as for castings general, large

of molten

In

which

I have made

allowed

the

by

a number

dimensions

of

because of

a speed

furnace,

the

action

equi temperature cm. in diameter,

2.2

of times and which the

of

as

were low

the largest as 4 mm.

an

hour is desirable, while for small castings I have used speeds up to 60 cm. per hour. It is in general true that it does no harm to err on the side of too great slowness, but this does not seem to be true for bismuth and tellurium, for which there is doubtless a rather definite optimum

speed

for

any

given

diameter

and

external

conditions.

It is important that air drafts be kept from the emerging mold, as To avoid otherwise new centers of solidification may be started. drafts the mold may be lowered into a pipe closed at the bottom end, with its upper end tightly pressed against the lower end of the furnace. If cooling in an oil bath is preferable to cooling in the ai