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Submitted on 1 Jan 1972
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”DIFFUSE-TO-SHARP” FERROELECTRIC PHASE TRANSITION SYSTEMS Pb(B’0.5 Nb0.5)1-x B”x O3
WHERE B’ = Fe OR Sc AND B” = Zr OR Hf
M. Valenta, F. Kuchar, P. Frankus
To cite this version:
M. Valenta, F. Kuchar, P. Frankus. ”DIFFUSE-TO-SHARP” FERROELECTRIC PHASE TRANSI- TION SYSTEMS Pb(B’0.5 Nb0.5)1-x B”x O3 WHERE B’ = Fe OR Sc AND B” = Zr OR Hf. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-247-C2-248. �10.1051/jphyscol:1972285�. �jpa-00215021�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-247
DIFFU SE-TO- SHARP >> FERROELECTRIC PHASE TRANSITION SYSTEMS Pb(B;., Nb,.5),-x B," 0, WHERE B' = Fe OR Sc AND 23" = Zr OR Hf (*)
M. W. VALENTA, F. KUCHAR and P. FRANKUS Institut fur Angewandte Physik der Universitat Wien A-1090
and Ludwig Boltzmann-Institut fur Festkorperphysik A-1060, Vienna, Austria
R6sum6. - Nous rapportons le comportement de la polarisation spontanke en fonction de la temperature pour des composes choisis parmi les systhmes ferroelectiques ?diffusion restreinte i Pb(B6,s Nbo, s ) I - ~ Bi 0 3 , oh B' = SC ou Feet B" = Zr ou Hf.
On observe des transitions de premier ordre et des transitions semblables A celles de premier ordre.
Abstract. - We report the behavior of the spontaneous polarization as a function of tempe- rature for selected compositions in the so-called diffuse-to-shaq ferroelectric systems Pb(B6.5 Nbo.5)l-z Bi 0 3 , where B' = Sc or Fe and B" = Zr or Hf. First order and first order-like ferro- electric transitions are observed.
In << complex )> perovskite-type ferroelectrics of the form A(B, B, ...) O,, it is now well known that one observes a (( diffuse )) phase transition [I]. The dielec- tric constant, E , versus temperature, T, curve is relati- vely broad and the spontaneous polarization, P,, can be observed at temperatures many degrees above T,, the temperature where the peak in the dielectric constant occurs. Several authors have offered some explanations for the presence of a diffuse ferroelectric phase transition [I]-[5]. As one might suspect, there is not unanimity among these authors, but there do exist areas of overlap.
Since we believe that probably one of the most important, distinctive properties demonstrated by a ferroelectric in still PC, a careful measurement of PJT) ". - (and also the remanant polarization, P,(T)) was under- taken. In the measurement of P, a Sawyer-Tower circuit [6] modified according to Diamant et al. [7]
was employed. Figure 1 shows a typical hysteresis loop.
In OUI study we have chosen solid solutions of Pb(Sc0.5Nb0,5)03 (PSN) and Pb(Fe~.5Nb~.5)03 (PFN) with PbZrO, (PZ) and PbHfO, (PH). Smolensky et al. [8] first reported PSN to be ferroelectric with a Curie temperature Tc = 900'2. Kuchar [9] later showed that PSN has a diffuse ferroelectric transition.
PFN was reported to be ferroelectric with a Curie temperature of 1120C by Smolensky et al. [lo].
Subsequently Isupov [ l l ] et al. showed that PFN did not demonstrate any phase transition broadening.
Figure 2 gives a good indication of the behavior of
(*) Work supported by the << Fonds zur Forderung der Wis- sen-schaftlichen Forschung ih ~sterreich s and, in part, by the
cc Ludwig-Boltzmann-Gesellschaft D, Austria.
FIG. 1. - Pb(Sco.gNb0.5)o. 15Zr~. 8 5 0 3 exhibits a typical hyste- resis loop at room temperature (25 OC) for our ferroelectric solid solution systems. Ps = 36 pC/cm2 for an applied electric field
of about 15 kV/cm at 50 Hz.
P,(T) as a function of Zr concentration in the (PSN),-, (PZ), and (PFN),-, (PZ), systems. Tc indi- cates the temperature at which the peak in the dielectric constant occurs. One can easily see from figure 2a that the PSN-PZ system has phase transitions that appear to become more first-order-like as the concentration of Zr is increased. I t is important to note that P, # 0 above To in a diffuse transition. One observes in figure 2b a discontinuous drop in P, at Tc and concludes that the phase transitions in the PFN-PZ system are first order. It may be tempting to make the claim that the ferroelectric phase transition is second order when it is diffuse, or at least in case of PSN. Of course, this
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972285
C2-248 M . W . VALENTA, F. K U C H A R AND P. FRANKUS
\ I
\ . L
0 50 IM 1% m 2%
TEMPERAME I .C 1
FIG. 2. - Ps(T) and Pr(T) of a) P ~ ( S C ~ . ~ N ~ ~ . ~ ) I - ~ Z ~ X O ~ for x = 0.2 and 0.85 at 50 Hz, b) Pb(Feo.sNbo.5)1-zZrz03 for
x = 0.28 and 0.90 at 50 Hz.
would be premature at this time and more work must be done.
The same systems with Zr replaced by Hf are shown in figure 3. From what we have seen above, the PSN- PH system offers no surprises : its behavior is similar to the PSN-PZ diffuse system, as one might expect.
However, in the PFN-PH system, figure 3b, a first order transition is heralded by the discontinuous drop in P, at the higher Hf concentration, while the lower Hf concentration shows typical diffuse behavior.
It now appears that the observed diffuseness may be due to fluctuations which make possible the simulta- neous presence of two phases, one ferroelectric and the other not, above and below T,. This is more in the spirit of Rolov [3] and Fritzberg [4] than Smolensky [l]
and Isupov [2]. However we depart significantly from these authors in stating that these fluctuations are a more general phenomenon observed in perovskite- related, and possibly oiher structures, having some essential characteristic of a second order phase transi- tion, i. e., the substances need not be ferroelectric (e. g., SrTiO,) and need not be purely second order (e. g., SbSI). When they are ferroelectric, the observa- tion of a hysteresis loop, P,(T) and P,(T), simply
0 YI I@ M
TEMPE- PC1
FIG. 3. - Ps(T) of a) Pb(S~o.sNbo.5)1-~Hf~O3 for x = 0.20 and 0.67 at 50 Hz, b) Pb(Feo.sNbo.s)~-~Hf~O~ for x = 0.20
and 0.90 at 50 Hz.
enables one to deduce the presence of the two phases.
When our substance is not a ferroelectric, other means of detection are necessary.
Note Added in Proof. - In our reply to Dr H.
D. Megaw's question as to what we meant byfluctua- tions, we stated that they appear to be ferroelectric (FE,) regions occurring in a non-FE background above T,. Presumably near a second order phase transition (2-OPT) one expects large fluctuations but not necessa- rily in the case of a 1-OPT where two phases can co- exist. In our experiments the applied electric field may simply be easil y catching )) these F E regions for us or may very well be inducing them ; this is a question we must still decide. Our first suspicion that F E regions can exist far above T, comes from studying the KDP-type work of Blinc and Bjorkstom (Phys. Rev.
Letters, 1969, 23, 788). Recently the beautiful work of Blazey (Phys. Rev. Letters, 1971, 27, 146) reinforced our beliefs, though it must be remembered that SrTiO, is not FE. Presumably the 105 OK transition in SrTiO, is a 2-OPT. However, one cannot escape the nagging thought that time has shown thought-to-be 2-OPT to be, instead, 1-OPT ! All these observations are generally related, at this time we do not know how, but possibly FE-related diffuse phases transitions may eventually jar open that door further.
References
[I] See, e. g. the review by : SMOLENSKY (G. A.), J. Phys. [7] DIAMANT (H.), DRENCK (K.) and PEPINSKY (R.), Soc. Javan (Suvv1.). 1970.28.26. Rev. Sci. Znstr., 1951,28,30.
[2] I s u ~ o v (v.~A.),' F&: tverd. ~ela,' 1963, 5, 187. [8] SMOLENSKY (G. A.), ISUPOV (V. A.) and AGRANOV- [3] R o ~ o v (B. N.), Proceedings of the International SKAYA (A. I.), Fiz. tverd. Tela, 1959,1, 170.
Meeting on Ferroelectricity (Institute of Physics of [9] KUCHAR (F.) and VALENTA (M. W.), Phys. stat. sol.
the Czechoslovak Academy of Sciences, Prague), (a), 1971, 6,525.
1966, 1, 154. [lo] SMOLENSKY (G. A.), AGRANOVSKAYA (A. I.),
[4] FRITZBERG (W. J.), ibid., p. 163. P o ~ o v (S. N.) and ISUPOV (V. A.), Zh. tekh. jiz., [5] SMITH (J. W.) and CROSS (L. E.), Ferroelectrics, 1970,1, 1958, 3, 2152.
137. [Ill I s u ~ o v (V. A.), AGRANOVSKAYA (A. I.) and KHU-
f6] SAWYER ( C . B.) and TOWER (C. H.), Phys. Rev., 1930, CHUA (N. P.), IZV. an S. S. S. R., ser.JiZ., 1960,24,
35,269. 2171.
