HAL Id: jpa-00214993
https://hal.archives-ouvertes.fr/jpa-00214993
Submitted on 1 Jan 1972
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
PHASE DIAGRAM OF Na(DxH1-x)3(SeO3)2 SYSTEM vs CONCENTRATION, TEMPERATURE, FIELD
AND PRESSURE
L. Shuvalov, A. Shirokov, N. Ivanov, A. Baranov, L. Kirpichnikova, N.
Schagina
To cite this version:
L. Shuvalov, A. Shirokov, N. Ivanov, A. Baranov, L. Kirpichnikova, et al.. PHASE DIAGRAM OF Na(DxH1-x)3(SeO3)2 SYSTEM vs CONCENTRATION, TEMPERATURE, FIELD AND PRES- SURE. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-165-C2-167. �10.1051/jphyscol:1972257�.
�jpa-00214993�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-165
PHASE DIAGRAM
OF Na(D,H, -x)3(Se0,), SYSTEM
YSCONCENTRATION, TEMPERATURE, FIELD AND PRESSURE
L. A. SHUVALOV, A. M. SHIROKOV, N. R. IVANOV, A. I. BARANOV, L. F. KIRPICHNIKOVA and N. M. SCHAGINA Institute of Crystallography of the Academy of Sciences of the USSR Moscow, USSR
R6sum6. - On montre que les cristaux Na(DZH1-+)3(Se03)2 sont isotopiquement non iso- morphes. On trouve que le champ klectrique externe E y klargit de faqon importante les zones de tempirature et concentration oh existe une composante y de la polarisation spontanke ; la pression hydrostatique agrandit la zone de concentration ou existe Psy et provoque une nouvelle phase dont les propriktes d6pendent du champ Ey.
Abstract. - It is shown that Na(DzH 1 -%) 3(Se0 3)2 crystals are isotopically nonisomorphous.
It is found that external electric field E, significantly widens temperature and concentration regions of existence of y-component of spontaneous polarization ; hydrostatic pressure widens concentration region of existence of P,, and induces a new phase whose properties depend on field Eu.
Recently we have found [l, 21 that
crystals (STDHS) are isotopically nonisomorphous (i. e. they have a different number, subsequence and symmetry of ferroelectric phases at different D concentrations) ; the physical natures of P,, ( z PSI)- and PS,-components of spontaneous polarization are different. These unusual properties make detail inves- tigation of phase diagram of STDHS crystals os x (concentration of D), T (temperature), E (electric field) and p (pressure) very interesting.
xT-diagram. -'As was shown in [I], [2] and confirmed in [3] xT-diagram of STDHS (Fig. 1) can be subdivided into three concentration regions with
FIG. 1. - Phase xT-diagram of Na(DZH1-Z)3(Se03)2 crys- tals ; D concentration is corrected in cornparision with data
of [I, 21.
different subsequences of phase transitions : I : (at 0
<
x 5 0.05) ao/3
ct y, I1 : (at 0.05 5 x 5 0.3) a t+ y' op
t,y, I11 : (at 0.3<
x 5 1) a tt y. Point symmetries of the phases are 2/m(a), I@) and m (y and y'). a-phase is paraelectric, P-phase is ferro- electric with two independent components of P, (P,, and P,,), y'-and y-phases are ferroelectric with one component of P,(P,,).xTE-diagram. - External electric field E, signifi- cantly changes xT-diagram. In region I Ey as usual shifts temperature of transition of the 1st order Tap [4]. In region I1 double Py(Ey)-loops are obser- vable in the whole, of y'-phase at E, exceeding some critical value E,""'. Therefore field Ey widens the region of temperature stability of P-phase up to the complete disappearance of y'-phase. If one goes up from TuTB or if x increases E,"" increases too.
Let us consider in greater detail the effect of field E, in region 111. The effect was fixed by means of observations of dielectric Py(Ey) and electrooptic cpy(Ey) loops (angle q describes optical indicatrix orientation, which is sharply different in different phases). At T < T,, near the T,, indicatrix orientation in the weak field corresponds to y-phase, in the high field - to P-phase (Fig. 2a). There are two critical fields : EYB-for the field-induced transition from y-into /3-phase and ED,-for the opposite transition ; the diffe- rence between them characterizes the field hysteresis which is evidence of the 1st order of transition.
EYS and EBy depend on T so that they decrease with T decreasing. In the process of this change Ep, turns into zero (Fig. 2b) and then becomes negative (Fig. 2c).
Starting from the last T virgin and repeated curves
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972257
C2-166 L. A. SHUVALOV ET COLL.
FIG. 2. - Electrooptic (upper drawings) and dielectric (lower drawings) hysteresis loops at x % 0.5 and different T :
-
71 (a),.- 84 (b), - 90 (c), - 102 OC (d).
qy(E,) become different. At some To (Fig. 3)
1
EBYI
becomes equal to EYa. Beginning from the To the field E, 2 Eyp irreversibly transforms y-phase into P-phase (Fig. 2 4 .
-
Phase pT-diagrams for different x values : x = 0 (I), 0.1...
(2), 0.2...
(3), 0.5 ... (4).FIG. 3. - Phase E, T-diagram (p = po, x E 0.5).
Such effects were observed nearly in the whole of region 111. It is only for x 2 0.9 that we were not able to induce P-phase due to the nearness of Eya to the breaking field.
Thus sufficiently large field Ey inducing P,, widens not only the temperature region of stability of j3-phase but also the concentration region of its stability apparently up to x = 1. Such effect of the field Ey allows us to suppose that in y-phase there may be an antiferroelectric arrangement of dipoles along the
Y-axis.
xTp-diagram. - As we have reported [5], [6], hydrostatic pressure p in region I firstly shifts a -j3 transition towards low T, then the line Tap splits up giving rise to a new &phase existing only at high p (Fig. 4, curve 1). (Recently Dr. G . A. Samara using the method of gas compression has checked this result at our request and confirmed it [7].)
In region I1 with p increasing the lines T,,, and Typo draw together and then merge into line T4 (yl-phase
disappears). As in region I further increase of p leads to the split of a -,B transition, as a result &phase appears. Thus in this case pT-diagram has two triple points (Fig. 4, curve 2). With increase of x they move to each other and merge at x x 0.2 (Fig. 4, curve 3)- At further x increasing pT-diagram qualitatively does not change.
FIG. 5. - Phase pxT-diagram.
PHASE DIAGRAM OF Na(DZH1-%)3 ( S e O h SYSTEM vs CONCENTRATION C2-167 We have found that in region 111 a t,y transition
shifts toward low T with increase of p and then line T,, splits up, as a result &phase appears (Fig. 4, curve 4). In the interval of p used (up to 12 kbar)
&phase was found up to x sz 0.5. Apparently &phase will appear at higher p for the NaD,(SeO,), crystal as well. It is interesting to note that recently we have found 6 o /3 transition in region I11 with T decreasing (Fig. 4, curve 4). The full xTp-diagram is shown on the figure 5.
Thus P,, not existing in STDHS at high x values can be induced by Ey and by p.
The properties of the new high-pressure 8-phase are greatly influenced by d. c./a. c. field E,, [2], [6]. If E, exceeds some critical value permittivity E, goes up sharply and irreversibly. So we can suppose that a new &-phase appears in this case. Absence of P(E) loops for any direction in the crystal in both &and
&-phases apparently shows their nonferroelectric nature.
References
[I] SHUVALOV (L. A.) et al., Zh. eksper. teor. Fiz. (Letters), [4] BLINC (R.), LEVSTIK (A.), Phys. Stat. Sol., 1970, a 2,
1968,8,235. K 131.
L2] SHuvALov A-) et az., J. Phys. Sot. Japan. Suppz., [5] SHIROKOV (A. M.) et al., Phys. Letteus, 1969,29A, 559.
1970, 28, 75.
[3] MIKI (H.), MAKITA (Y.), J. PAys. So,-. Japan., 1970, [61 SHUVALOV (L. A.) et al., ~ r i s t a l l o ~ r a f i ~ a , 1970,15, 1011.
28,143. [7] SAMARA (G. A.), Private communication.
