Dielectric and mechanical loss in the system Pb3MgNb2O9 - Pb3NiNb2O9

Mat. Res. Bull. Vol. 3, pp. 877-884, in the United States.

1968.

Pergamon

Press, Inc.

Printed

DIELECTRIC AND MECHANICAL LOSS IN THE SYSTEM Pb3MgNb209 - Pb3NiNb209

L. E. Cross and J. W. Smith* Materials Research Laboratory and Department of Electrical Engineering The Pennsylvania State University University Park, Pennsylvania 16802

(Received

September

16,

1968;

Communicated

b y R. R o y )

ABSTRACT The dielectric loss and internal friction have been measured over a range of temperature for ceramic bar samples of compositions in the system lead magnesium niobate - lead nickel niobate. The dielectric relaxation is accompanied by a correlated dispersion in the mechanical properties of all members of the system tested. The results are shown to be consistent with the model of a broadened or diffuse phase change to a ferroelectric state which was proposed by Smolenskii to account for the dielectric properties in this system.

Introduction A number of perovskite type dielectrics of complex composition have attracted considerable attention in recent years because they combine some features of normal ferroelectric crystals with a marked time dependence of the dielectric properties evident at quite low audio frequencies.

Among these

materials, perhaps the most intensively studied have been the solid solutions of bismuth titanate in strontium titanate (Bi2/3x ,.

Sr(l_x)Ti03).. [Skanavi et

al. (l-3)]and the compounds lead magnesium niobate (Pb3MgNb209) and lead nickel niobate (Pb3NiNb209) by Smolenskii et al. (4).

It has been fairly well

established by Bokov and Mylnikova (5) that lead magnesium niobate is ferroelectric at; lower temperatures.

The time dependence of the polarization in

these materials is suggested to arise from a broadening of the Curie temperature transition, due to compositional heterogeneity, leading to the Presently with C o m i n g Glass Works, Coming, New York. 877

878

D I E L E C T R I C AND M E C H A N I C A L L O S S

Vol. 3, No. 11

coexistence of ferroelectric and non-ferroelectric material in the 'Curie range ' In the following paper, measurements of the internal friction as a function of temperature in ceramic samples of lead magnesium niobate (PMN) are reported.

These results are shown to be consistent with the model of a ferro~

electric with a diffuse or broadened phase transition.

Measurements have also

been made on solid solutions of lead magnesium and lead nickel niobate (PNN). These data show that both dielectric and mechanical spectra change continuously over the solid solution sequence and suggest that a similar mechanism is responsible for the properties of the nickel compound. Experimental Procedure Bar specimens of ~

and PNN were prepared from reagent grade chemicals.

The chemicals were mixed in the appropriate proportions, ground in a mortar and pestle and fired in a platinum crucible-for 2 hours at 850°C.

After sub-

sequent grindings and firings, the resulting compounds were pressed in a bar mold using a methocel carbowax binder. hours at I070°C.

The c~npounds were sintered for 3

The density of all the specimens was greater than 95% of

theoretical density. The resulting bars were cut into 3 1/4" lengths.

Their faces were

ground flat on a lapping wheel and the final finish was applied using #500 silicon carbide paper. 1/8".

The finished bars were approximately 3 1/4" x 5/16" x

Aluminum electrodes were then evaporated on the two opposing 3 1/4" x

5/16" faces and fine wire leads attached to the electrodes with small amounts of conducting epoxy.

Capacity and dielectric loss measurements were made by

means of a GRI650-A impedance bridge, The mechanical loss measurements were performed on a FSrster type apparatus (6) constructed in this laboratory.

In this device the specimen is sus-

pended from its nodes by two fine threads, one of which goes to a mechanical drive and the other to a vibration pickup.

The mechanical drive is used to

drive the specimen into resonance and the response of the vibrating specimen is monitored by the pickup.

The internal friction is then obtained from the

express ion

Q-l=

1 f

where f

o

(1) o

is the resonant frequency of the specimen and Af is the difference

between the two frequencies at which the value of the output from the pickup

Vol.

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11

DIELECTRIC

AND MECHANICAL

LOSS

879

was one-half the value at the resonant frequency. The low temperature mounted

apparatus

consisted

of a copper specimen chamber

on a copper stem supported by a brass tripod.

uated in the bottom of a large stainless coolant

This ensemble was sit-

steel dewar vessel.

The level of

(liquid nitrogen or dry ice) in the dewar was maintained

inch below the copper specimen chamber causing the temperature

about one

inside the

chamber to approach within 3 or 4 degrees to that of the coolant.

Tempera-

ture control was maintained by means of a small heater coil of chrome! wire situated

on the copper stem just below the specimen chamber and driven by a

variable transformer.

As long as the level of the coolant remained reasonably

constant in the dewar the temperature ± I°C.

in the chamber could be controlled with

The temperature within the chamber was varied at the rate of lO°C/hr. Experimental

Results

The experimental data for a pure I::'MN ceramic is summarized

6

___x ..... x

x

x x

5

x _.xx._..x_x x,

x xX

x

x% % x

K

x%%%

x\

x\x

Nb209

~x\\,

DIELECTRIC

LOSS

"

F

16 \

oJ

\

\

r,r)

-

"\'\ \

MECHANICAL

b

20

\

LOSS CURVES Pb3Mg

4

x

in Fig. i.

b

\ \

3

12 ×

x

CA:)

z

x~

-IL 2

8 xx

4

0

-6'o

-I00

-4'o

-2'o

TEMPERATURE

6

2'0

(°C.)

FIG. 1 Dielectric

and mechanical as a function

loss in ceramic Pb3MgNb209 of temperature

0 40

<% F-

880

DIELECTRIC

AND

MECHANICAL

LOSS

Vol. 3, No.

II

This was for a bar resonating at a frequency of approximately 2,300 KHz. Similar curves were obtained on a number of samples although the absolute loss levels varied slightly.

It is interesting to note that the mechanical loss is

high and almost constant up to a temperature of -25°C. Similar data for PNN and for a number of solid solutions between PNN and PMN are Sl~m~arized in Fig. 2.

z

/

I : ~ I ~ x Ni(l_X) Nb209

0.14 00

Two points are of particular interest.

X-O

x:N

OJ2 _

X=

. - . - . .

1.0-

::;:

m O.IC _ 008 00~ 004 w-

k'g..L

I

'

OD2

1 ,

I -150

,

I - 150

,

7.5

I - I00

,

I

,

-50 TEMPERATURE (°C)

I

0

~O_ 5D X

To 2.5 -200

,

I - I00

,

I - 50

,

I 0

TEMPERATURE (°C) FIG, 2 Dielectric and mechanical loss in the system Pb3Mg N i t l _~x , N b)2 0 9 ~

Vol.

3, No.

(a)

II

DIELECTRIC

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MECHANICAL

LOSS

881

The temperature of the 'break' in the internal friction curve, and

of the peak in the dielectric loss tangent, changes continuously with composition in the solid solution sequence. (b)

The shape of the mechanical loss curve also changes continuously

from an asymmetrical, very steep drop in PMN to a more or less symmetric loss peak in PNN.

The general dielectric loss level also decreased slightly as

the temperature was increased, but in no case was any discontinuity in the resonant frequency noticed.

Since Young's modulus is proportional to the

square of the resonant frequency for a bar vibrating in flexure (6), we can state that within the resolution of our apparatus (± 0.2 KHz), no discontinuity in Young's modulus was apparent. Discussion It is clearly seen that the internal friction and dielectric loss are intimately associated throughout the solid solution sequence.

This close

association, together with the demonstrated frequency dependence of the dielectric loss ( 4 ) i s

somewhat similar to that resulting from the stress and

field induced ordering of point defects (8).

Two features of the system

mitigate against such an explanation, however: (a)

Point defect ordering is not a common cause of pronounced relaxa-

tion in high permittivity materials. (b)

Neither PMN nor PNN are intrinsically defective in the sense that,

for example, bismuth strontium titanate is (2).

Also Smolenskii (4) has

shown that small variations in the compositions of the ceramic do not noticeably affect the dielectric properties. The strong evidence for ferroelectric behavior shown in PMN and, to a lesser extent, in PNN by Bokov and Mylnikova (5) leads us to conclude that the loss can be satisfactorily explained on the basis of ferroelectric behavior in the systems involved.

Phase transitions in solids, whether of a dis-

placive nature, or of an order-disorder type, are characterized by a sharp increase in the mechanical loss in the vicinity of the transition temperature. This behavior is attributed to the instability of the crystal lattice and to local stresses generated by the coexistence of two phases near the transition temperature. In ferroelectric materials, well below the Curie temperature, the internal friction is generally substantially higher than in the paraelectric state.

For example, data from Ikeda (7) for barium titanate ceramics are

882

DIELECTRIC

shown in Fig. 3.

.AND M E C H . A N I C . A L

LOSS

Vol. 3, No.

I1

This type of behavior has been attributed to piezoelectric

8 7 6 I¢)

_o5 K4

b3 2 I 0

50 I00 TEMPERATURE PC) FIG. 3

Mechanical loss in BaTiO 3 from the work of Ikeda (7)

and electrostrictive effects (7) and to the motion of domain walls (9,10). The dielectric loss is also generally higher in the ferroelectric region and shows a peak at some temperature below the Curie temperature (7,11). It is interesting to compare this behavior to that found in PMN.

The

mechanical loss level at lower temperature in what is believed to be the ferroelectric region is uniform and much higher than that in the paraelectric region, but the sharp peak, characteristic of normal phase transitions, is completely absent.

This, however, is just what would be expected if the

phase transition were distributed over a range of temperatures.

The energy

absorbed at a single temperature in a normal ferroelectric would be distributed over a range of temperature and the strong peak would be dropped into the background.

The loss processes inherent to the ferroelectric phase would

gradually absorb more energy as the temperature was lowered, and the net result would be a continuous increase in mechanical loss with decreasing temperature.

At sc~e temperature, where the transformation was substantially

complete, the mechanical loss would stabilize and further reductions in temperature would not affect it.

This is precisely the behavior shown in

Fig. 2. In the solid solution sequence, it is evident from the continuous variation of both the dielectric loss and internal friction peaks, that the same

Vol.

3, No.

ii

DIELECTRIC

type of processes

AND

MECHANICAL

are involved in both end members.

concluded that the ferroelectric

processes

involved

essentially of the same nature and differed

LOSS

883

Bokov and Mylnikova

(5)

in both materials were

only in degree~

the ferroelectric

nature of PMN being much the more pronounced. The continuous

gradation of the magnitudes

adding PNN to PMN and the essential

of the losses observed upon

similarity of the loss characteristics

of

the end members would tend to support this view. It would seem, then, that the increase in the mechanical temperature

is lowered is a monitor

of the transformation

for a peak to form in the mechanical cates that the transition

loss as the

range.

loss of the nickel-rich

The tendency

compounds

indi-

losses, which are masked by the marked ferroelectric

losses in PMN, are not masked in PNN where the ferroelectric

behavior is

presumably much less pronounced. The nature of the ferroelectric

loss processes

is not clear.

Both

electrostriction

and domain wall motion may contribute

ferroelectrics.

There is as yet no direct evidence for domain formation in

the transition region;

however,

been observed in PMN (5). from 90o wall motion,

at lower temperatures,

Mechanical

to losses in normal

domain structures have

losses from domains could only occur

since 180 ° domains are direction

insensitive.

That is,

the energy of a 180 ° domain in a stress field is the same in both directions. In this we are assuming that the domains normally found in ferroelectric

are of the same nature as those

perovskites,

although much smaller.

Summary Measurements

have been made of the dielectric

in ceramie bars of lead magnesium niobate, intermediate

solid solutions.

of a ferroelectric friction

loss and internal friction

lead nickel niobate,

The loss data can be interpreted

with a diffuse

or broadened phase transition.

and several on the model The internal

appears to be a sensitive monitor of the phase transition region.

The results for the solid solutions between the end members

show a continuous

variation

in properties

and it is probable that both are ferroelectrics

essentially the same nature.

The ferroelectric

niobate is much more pronounced,

behavior

of

in lead magnesium

however.

Acknowled~nent This research was conducted under Atomic Energy Commission

AT(30-1)-~581.

Grant No.

884

DIELECTRIC

AND

MECHANICAL

LOSS

Vol. 3, No. 11

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G. I. Skanavi and E. N. Matveeva, Soy. Phys.-JETP 3, 905 (1957).

2,

G. I. Skanavi. I. M. Ksendzov, V. A. Grigubenko and V. G. Prokhsvatilov,

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A . M . Kashtanova, N. N. Kurtseva, and G. I. Skanavi, Bull. Acad. Sci., U.S.S.R. Phys. Ser. 24, 109 (1960).

4.

G.A. Smolenskii and A. I. Agranovskaya, Soy. Phys.-Solid State l, 1429 (1959) •

5.

V.A. Bokov and I. E. Mylnikova, Sov. Phys.-Solid State 3, 613 (1961).

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T. Ikeda, J. Phys. Soc. Japan 13, 809 (1958).

8.

J. B. Wachtman, Phys. Rev. l~l, 517 (1963).

9.

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lO.

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