the inorganic fluoride and oxyfluoride ferroelectrics...j phys. iii ftance 7 (1997) 1129-1144 ju~ie...

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The Inorganic Fluoride and Oxyfluoride FerroelectricsJean Ravez

To cite this version:Jean Ravez. The Inorganic Fluoride and Oxyfluoride Ferroelectrics. Journal de Physique III, EDPSciences, 1997, 7 (6), pp.1129-1144. �10.1051/jp3:1997175�. �jpa-00249637�

https://hal.archives-ouvertes.fr/jpa-00249637https://hal.archives-ouvertes.fr

J Phys. III Ftance 7 (1997) 1129-1144 JU~iE 1997, PAGE 1129

The Inorganic Fluoride and Oxyfluoride Ferroelectrics

J. Ravez

Institut de Chimie de la MatiAre Condensde de Bordeaux, CNRS,

162 avenue du Docteur Albert Schweitzer, 33608 Pessac Cedex, France

(Received 20 June 1996, accepted 12 November 1996)

PACS 77 80.-e Ferroelectricity and antiferroelectricity

Abstract. The ferroelectric fluorides belong to six fairiilies of type (NH4)2BeF4, BaMnF4,SrAlF5, Na2MgAlF7, K3Fe5F15 or Pb5Cr3F19. The oxyfluorides can be separated in two

groups: ii the true oxyfluorides with a relatively high F/O value (K3Mo03F3, Na5W30gF5,Pb5W30gFio, B12Ti04F2, .:); ii) the compositions derived from ferroelectric oxides (perovskite,

tetragonal tungsten bronze, pyrochlore, LiTa03, ...) characterized by a continuous F-O substi-tution. The phase transitions and the physical properties are discussed The origin of the

spontaneous polarization is described structurally. The variations of the Curie temperaturewith the type of substitution are related to chemical bonding. The potential interest of thesematerials for applications is briefly given.

R4sumd. Les ferrodlectriques fluords appartiennent h six farnilles de type (NH4)2BeF4,BaMnF4, SrAlF5, Na2MgAlF7, K3Fe5F15 ou Pb5Cr3F19. Les oxyfluorures peuvent Atre s4pa-

rds en deux groupes ii les oxyfluorures "vrals" comportant un rapport F/O relativementdlevd (K3Mo03F3, Na5W30gF5, Pb5W30gFio, B12Ti04F2, .), ii) les compositions ddrivdes desoxydes ferrodlectriques (perovskite, bronze quadratique de tungstAne, pyrochlore, LiTa03, ...)

et caract4ris4es par une substitution F-O continue. Les transitions de phases et les propr14t4sphysiques sont analys4es L'origine de la polarisation est prdcisde sur le plan structural. Les va-riations de la temp4rature de Curie avec le type de substitution sont relies h des considdrations

de liaison chimique. L'int4rAt potentiel de ces mat4riaux pour les applications est brikvementabord4.

1. Introduction

Inorganic ferroelectrics are mainly oxides (families KDP, perovskite, tetragonal tungsten bronzes,LiNb03, Pyrochlore, boracite, Aurivillius phases, ...). Ferroelectric fluorides are much less nu-

merous; one of the causes is that although stable up to about 400 K, the high temperaturepreparation of crystals and ceramics requires particular care to prevent hydrolysis. Some com-

pounds are declared as ferroelectrics from theoretical studies (HF, PbF2, NaCaF3, ...) Ii, 2].Nevertheless the proofs of ferroelectric properties have been demonstrated only for the six

following families: (NH4)2BeF4, BaMnF4, SrAlF5, Na2MgAIF7, K3Fe5F15 and Pb5Cr3Fig.

@ Les llditions de Physique 1997

1130 JOURNAL DE PHYSIQUE III N°6

The ferroelectric oxyfluorides form a bridge between the fluoride and oxide families; thecorresponding research has been on the increase for about forty years:

Number of publications on oxyfluoride ferroelectrics

1957-1966 1967-1976 1977-1986 1987-1996

5 16 39 59...

These materials may be separated in two sub-groups:

the "true" ferroelectric oxyfluorides with a relatively F IO ratio and belonging to familiesin which fluorides and oxides are not necessarily ferroelectrics; as an example Na5W309F5is ferroelectric although Ca5Te3015 and Na5A13F14 are not;

oxyfluorides derived from ferroelectric oxides by a generally progressive and weak fluorine-

oxygen substitution.

Table I gives the list of main fluoride and "true" fluoride families known at the present time.

2. The Ferroelectric Fluorides

2.1. (NH4 )2BeF4 Ammonium fluoroberyllate is the longest known ferroelectric fluoride [3].Its crystalline network is composed of distorted (BeF4)~~ tetraedra. Although of close struc-ture, however it is not isomorphous of the ferroelectric sulfate (NH4)2S04 (19].

2.2. FAM~LY BaMF4 (M=

Mg, Mn, Fe, Co, Ni, Zn). The BaMF4 fluorides are ferro-electric up to their melting temperature [4]. The value of the spontaneous polarization is close

to 10 ~C cm~~ at 300 K. The inversion of the polarization corresponds to a shift of the Ba~+

cation along the c-polar axis of the orthorhombic crystalline unit cell (mm2 point group); it

goes with the rotation of octahedra linked by corners leading to layers separated by the Ba~+

cations (Fig. 1).These fluorides are bidimensional ferroelectrics.

2.3. FAM~LY ABFS (A=

Sr; B=

Al, Cr, Ga A~D A = Ba; B = Ti, V, Fe). It is

an analysis of the crystalline structure which made it possible to predict the ferroelectric

properties of displacive type in SrAlfs (Tcr~

700 K) Physical studies on crystal have shownthe existence of piezoelectric and second harmonic generation properties. Two solid solutionsof Bafei-~In~F5 and Bai-~Sr~FeF5 compositions have shown that the value of Tc decreases

with the size increase of the cation in 6 C-N- and with the size decrease of the alkaline-earth

cation [6]. A similar result was obtained for perovskite phases derived from BaTi03 (forexample BaTii-~Zr~03 and Bai-~Sr~Ti03)1 this result is correlated with steric and bondcovalency effets [20j.

2.4. FAM~LY Na2MgAlF7 Second harmonic generation studies performed at 300 K made itpossible to confirm the polar point group 4mm for Na2MgAlF7 and Na2NiMF7 (M = Al, Fe)The phase transition temperature varies with composition; it takes place at T > 725 K [7].

2.5. FAM~LY K3Fe5F15. Coupled ferroelectric and ferroelastic properties were predicted

from atomic po#iUions of K3Fe5F15. The crystalline network of "tetragonal tungsten bronze"

type shows an orthorhombic distortion at 300 K. The Curie temperature (Tc r~ 490 K) wasdetermined by calorimetric and dielectric measurements, and alsoj by the disappearance of the

ferroelastic domain structure under polarized light microscope [8].' The composition K3Fe5F15

N°6 INORGANIC FLUORIDE AND OXYFLUORIDE FERROELECTRICS 1131

~ ~ W-tO--

~ ~~ ~~~~~C° £ #q ~~# ~ ~

( jo .4 ~

~i~~ f

~°~ (

_d~

ill i$ zit ~~ ~~ ~) j~

~~ (q($~~ )~ ~j)~

j ~~ ~q~ ~i~~j~~ @i~i I($id $6.( £(I %jj(~i~~i$#~ ~~~ qo~~~o j~

b0jj ~

~ z ~+~~(©~ jj"j~q~ j(j ~~f~j~

(()(~~j~~j~ ~j§) ~iii(~(~~ti

tQ/l22 ~/~i$Z~Z~/

~ ~ ~ ~~§ j[ fly g @(g gg gt O .~ .~ ~ O .~ .~ .~ .~

zg @j~ .]@j ~~ ~

j m j~% ~j% ~~ ~$ ( flee ~4+ ++ +

j ~ et~j

I ~i~i~(~i (jj ~iCQ ~j~n ~

EE ~E~~

~ - ~~ l~ ~ ULDU LD~C ~/g ~/~j ( ~

~~~ ~~~~° ~A

~

~ ~~~ i~~ii~ fli~ ij~~'i ~j))~) II )

j ill~'~#2 if fl~ ~~

~


a~ t

~

a ,'

~"~~

'',

'

I

', Ps

-.

ni~~

' ~[ P's .I

(I ~

i

/'

.Ba i 'm- ~§f

~Bi' i

' i

,

F(21'

I

'

' i

' '

Fig. 1. Atomic arrangement for the two polarities of BaMF4.

implies the simultaneous presence of Fe~+ and Fe~+ cations. The spontaneous polarizationorigin is correlated with the displacements along the polar axis of Fe~+ and Fe~+ cations intheir octahedral sites, these cations being ordered in the crystalline network. Above Tc, theiron atoms are localised at the octahedron center and Fe~+ and Fe~+ cations are disordered in

some crystallographic sites [21]. This ferroelectric fluoride is thus both displacive and of theorder-disorder type. So, it is different from oxides (for example Ba2NaNb5015, Pb2 5Nb5015)

of displacive type for which it is not isomorphous. Moreover, as will be mentioned in theoxyfluoride section, a low rate of F-O substitution leads to the disappearance of the ferroelectricproperties. The solid solution K3-~fesfis (0 < x < 1) also leads jo the disappearance of thespontaneous polarization, the K+ defect involves a change of the Fe~+ /Fe~+ ratio which is notfavourable to the creation of an order between the two cations [22].

2.6. FAM~LY PbsCr3F19. Examination of the atomic positions of the polar crystallinenetwork (4mm point group) of PbsCr3F19 shows the Cr~+ cation to be off center from itsoctahedral site [9]. The ferroelectric-paraelectric transition at Tc

=555 K is of first order

type, in particular the birefringence sign changes abruptly at Tc (Fig. 2) [23]. The value of Tcvaries with the M~+ cation size in the series of isomorphous compounds PbsM3F19 (M

=Al, Ti,

V, Cr, Fe, Ga) of displacive type [24]. The PbsA13F19 compound shows a transition sequencevery rich in ferroic properties [25]:

V (4mm) ~ IV (4/m) ~ III (2/m) ~ II (4/m) ~ I (4/mmm)ferroelectric antiferroelectric ferroelastic paraelastic prototype

paraelectric


10~ An

A ~

j

i

Pi P~

i/$

~ j~i

i

i

_, ,

,1~,

300 400 500~ fi00 T(K))~/

Fig. 2. Temperature dependence of the birefringence for a Pb5Cr3F19 crystal.

A pyroelectric current and a piezoelectric resonance have been shown in phase V [26]. Fer-roelastic domains have been observed for phase III; the spontaneous strain appears abruptly

on heating at the IV-III transition; it decreases then progressively and cancels at the III-IItransition [27]. Figures 3 and 4 show a projection of the unit cell on xoy plane and the shift

of Al~+ cations in the octahedra forming chains which develop along the polar axis.The various distortions which appear in PbsA13F19 result from the association of both the

6(sp)~ lone pair of Pb~+ cation and the small size of the Al~+ ion.

3. "True" Ferroelectric Oxyfluorides

3.1. FAM~LY K3Mo03F3. Numerous A2BM03F3 IA, B=

K, Rb, Cs with rA+ > rB+and M

=Mo, W) show a crystallographic distortion of the prototype cubic phase (m3m)

of (NH4)3FeF6 type. The,ferroelectric properties which appear below Tc are coupled withferroelastic properties, Physical studies on a K3Mo03F3 crystal make it possible to visualizeferroelastic domains and to obtain both a P-E hysteresis loop and a pyroelectric current [28j.

The value of Tc decreases when Mo is replaced by W, but is much more sensitive to theB+ cation nature in the 6 C.N. site: the order which appears when B+ is smaller than A+

localized in the 12 C.N. site, leads to a decrease in both the octahedron distortion and the


°j fl~~~j © o

~jQ~~

~,,~.,

~p.~~~'

~;j~i~~

...fl~

~fbf~jy~~f ~~ ~J

alI.

~

@ Pb~'

Fig. 3. Crystallographic unit cell projection of the phase V of Pb5A13F19 along [001].

phase V phase IV (2V) phase ill phase11

. t+ . t+Az

.t +AZ

~j AZ

Fig. 4. Schematic shift of Al~+ cations along the (001) axis for the Pb5A13F19 various phases.

value of Tc (as an example, Tc(Rb3MOO~F~) = 538 K and Tc(Rb2KMOO~F3) = 328 K)[10,11, 29]. All ions of the ferroelectric phase are displaced from their ideal positions in the

prototype phase. Amplitudes and directions of atomic displacements show the crystal to be

a tridimensional ferroelectric. Such a result is in good agreement with the small value of thespontaneous polarization (0.I < Ps < 3 ~C cm~~). A F-O substitution leads to a decrease

in Tc [30j. Nine other compounds belong to this family, having the compositions A~TiOFSand A3M02F4 IA

=K, Rb, Cs; M

=Nb, Ta). They are also ferroelectric-ferroelastic and

generate second harmonics [31j. Recent studies also showed ferroelectric properties for thecompounds Na3M03F3 (M

=Mo, W) (Tc

~J

805 K); the harmonic yield in nonlinear optics ishere relatively strong (Rh/Rh(quartz)

mJ

40 at room temperature) [12, 32].


'Qj

z

xONa~

~

Fig. 5. Schematic view of the Na5A13F14 structure.

3.2. FAMILY B12Ti04F2. The three compounds B12Ti04F2 and B12MOSF (M=

Nb, Ta)have only one perovskite layer in a crystalline network of "Aurivillius phase" type. They show

a ferroelectric-paraelectric (mm2-4/mmm) transition [13]. A P-E hysteresis loop has beenvisualized. The close values of Tc (283 < Tc < 303 K) confirm that Tc is mainly influenced

by the polarizability of A"+ cations and by the number of perovskite layers in the family ofcomposition Am-p+iBip-2Bm(O, F)3m+1.

3.3. FAMILY Na5W30gF5. The compound Na5W30gF5 with crystalline structure derivedfrom that of the chiolite Na5A13F14 (Fig. 5) generates a second harmonic and shows coupled

ferroelectric-ferroelastic properties [14,33]. Ferroelastic domains have been observed on crystalunder polarized light microscope (Fig. 6). A detwinning of the crystal was obtained by appli-cation of an external mechanical stress leading to an increase in the pyroelectric coefficient asexpected when the two ferroic properties are coupled. A strong maximum of the permittivity

occurs at Tc (Fig. 7). The temperature dependence of the atomic positions showed the ap-pearance of the spontaneous polarization, for T < Tc, to be related to rotations of W(O, F)6octahedra around the a and b axes of the prototype tetragonal phase (4/mmm) [34]. Two

other transitions occur in the ferroelectric region of Na5W30gF5. Various substitutions (Mo,Ti, Nb, Ta to W; Li, K to Na; fluorine-oxygen) lead to a very rich family [35]. The value of Tcvaries with the size of the cations and with the bond M-X (X

=O, F) covalency. The partial

substitution of Li+ to Na+ made it possible to obtain crystals of very good optical quality andlarge size (mJ 2 cm3).


Fig 6. Ferroelastic domains of Na5W30gF5.

£'1 22

200

£~22

26 6

100

26 4

26 2~oo 600

2~~~~~~ljFig. 7 Temperature dependence of the permittivity for a Na5W30gF5 crystal


3.4. FAMILY Pb5W30gFjo. Ferroelectric properties were predicted from the atomic ar-rangement of Pb5W30gFjo which derives from that of Pb5Cr3Fjg. The possibility of reversing

the spontaneous polarization, characteristic dielectric properties and second harmonic gen-eration led to confirming such an hypothesis [36]. The Curie temperature (Tc ~ 785 K)corresponds to a ferroelectric (14)-paraelectric (IT) transition. Two isotypic phases have the

same properties- Pb5Mo30gFjo and fb5T1303F16 [16].Crystals of size 1.5 x 1.5 x 5 mm3, of composition AS Nb30F18 IA = K, Rb) and of crystalline

structure close to that of Pb5W30gFio were obtained by slow cooling after dissolving in a HFsolution. A piezoelectric resonance and a pyroelectric current were observed between 300 and

500 K11?].

4. Oxyfluorides Derived from Ferroelectric Oxides

4.I. PEROVSKITE, TETRAGONAL TUNGSTEN BRONZE AND PYROCHLORE TYPES. 0Xy-genated phases of perovskite, tetragonal tungsten bronze and pyrochlore type have ferroelectricproperties. Their crystalline network shows octahedra linked by corners. The fluorine-oxygen

substitution associated with a cationic substitution to ensure electric neutrality gives rise to

a decrease in the Curie temperature, the spontaneous polarization and the harmonic yield innonlinear optics. The decrease in Tc may be very abrupt even for low substitution rates. Fig-

ure 8 shows, as an example, that the replacement of only one oxygen on 60 (0.25 /15) leads toa decreasing in Tc of about 600 K. Figure 9 shows clearly the decrease in Tc for such materialscompared to true oxyfluoride ferroelectric [37]. The distortion of the MX6 IX = O, F) octahe-dra related to the displacement of the M"+ cation out of the octahedron center is responsiblefor ferroelectricity. When fluorine replaces oxygen, the M-X bonds become less covalent, andthe anisotropy decreases. So the increase in temperature up to Tc leading to more isotropicbonds (paraelectric phase) decreases.

When other transitions exist in the ferroelectric region, their temperature does not neces-sarily decrease when the amount of fluorine increases. Figure 10 shows the case of the solid

solution Ba(Ti~_~Li~)03-3~F3~ for which Ti (orthorhombic-tetragonal transition) decreasesand T2 (rhomboedral-orthorhombic transition) increases. This system is very attractive. Infact, for composition 0 < a~ $ 0.03, the behavior is of classical ferroelectric type as for BaTi03On the contrary for 0.03 < a~ £ 0.15, it is of relaxor type: when the frequency increases, the

temperature Trr of e[' (max) increases, the value off( decreases progressively and el' remainsrelatively constant, its value being relatively strong ifl'

mJ100 at 10~ Hz) for T < Trr [38, 39].

In addition, they show a microwave relaxation whose origin is related to 6 C-N- cation motions,along correlation chain in a double well potential model [40].

4.2. LiTa03 TYPE. Oxyfluorides of the LiTa03 type have been obtained in LiNb03 -LiF-NbO2F, LiTa03-LiF-Ta02F and LiM03- "LiMgF3" (M

=Nb, Ta) systems. The crystalline

network is composed of octahedra linked by faces in the polar direction and by edges in otherdirections. The variation of Tc is correlated to the variation of the covalency degree of the M-X

(X=

O, F) bonds, and to the cationic non stoichiometry [41, 42]. The fluoride MgLiF3 usedas sintering additive is of great interest for densifying LiTa03 ceramics at low temperature(Fig. 10) [43].

4.3. Pb5Ge3011 TYPE. The replacement of oxygen by fluorine goes with the creationof defects in the site of Pb~+: (Pbi-~/2a~/2)5Ge3011_5~F5~ (0 < a~ < 0.10). The Curie

temperature decreases with x from 453 to 355 K [44].


Tc

800

0 05 x

Fig. 8. Variation of Tc with ~ for ceramics of composition Ba2-zNazNb~Oi5-zfz

t

~ j~~~~~#$° "Bronzes"

0 0.4 0.5 ~=_o+F

Fig. 9. Variation of Tc with the rate of F-O substitution for a true oxyfluoride ferroelectric andfor oxyfluorides derived from ferroelectric oxides


T

Tc

T2

200""j

T

(-i -----

0 0 05 0 10 0.15 0.30 x

Fig. 10. -Variation of the transition temperature with ~ for ceramics with compositionBa(Ti~_~Liz)03-3zF3z.

4.4. (NH4)2S04 TYPE. The two solid solutions of compositions (NH4)2(S04)1-~ (BeF4)~(0 < a~ < 0.22; 0.70 < x < I) derive from the two ferroelectric compounds (NH4)2S04(Tc

=223 K) and (NH4)2BeF4 (Tc

"175 K). The Curie temperature decreases when the

composition deviates from one or the other of the limit phases [19].

4.5. BaA1204 TYPE. Non-linear properties have been detected in crystals and ceramics of(Bai-~A~)(A12-2~L12~ )04-4~F4~ IA

=Sr, Ba, Pb) (0 < z < 0.30) compositions. The Curie

temperature varies from 240 to 426 K, the spontaneous polarization from 8 to 15 ~C cm~~

and the coercive field from 5 to 2 x 10~ V m~~. Although having a spontaneous polarization,these materials are in fact structurally ferrielectric [45-47].

4.6. SIMULTANEOUS FLUORINE-OXYGEN AND LEAD-ALCALINE EARTH SUBSTITUTIONS.

The F-O substitution generally leads to a decrease in Tc. Moreover, the Pb~+ A~+ (A = Sr,Ba) substitution in oxidized titanates, for an example, leads to an increase in Tc in correlationwith the strong distortion created by the 6(sp)~ lone pair of the Pb~+ cation. When F~ andPb~+ ions are introduced together into the crystalline network, two competitive effects appear.The anionic substitution firstly causes a decrease in Tc followed by an increase in Tc, thusgiving a minimum of Tc for a definite composition (Fig. ll for example) [47].


Tc (K)

450

400

350

300

250

200

0 0.02 0.04 0.06 X 0.08

Fig. 11. Variation of Tc withz

for ceramics with composition Bai-zPbz(A12-2~L12~)04-4«F4~

5. Some Potential Applications

5.I. DIELECTRICS FOR TYPE I CAPACITORS. The decrease in the Curie temperature byF-O substitutions may make it possible to situate the paraelectric phase in the usual temper-ature range for applications (250 to 350 K). In this temperature domain, the still high values

of the permittivity e( and its stability in frequency mean that such materials are of potentialinterest as dielectrics for type I capacitors. For example, let us consider the values of the

following pyrochlore oxyfluoride Pbi 8oZno15Nao o506 95Fo05

if)r-

200; tanmJ

3 x 10~~) [48j.Thick films have been prepared by 8erigraphy; the permittivity 18 very stable If( +J 80 from 10~

to 10~ Hz) and the dielectric losses are very low (tan < 10~~) [49j. Thin films have also beenobtained by cathodic sputtering, but the amorphous character of the films causes a decrease

in permittivity if(+J

30) [50j.

5.2. DIELECTRICS FOR TYPE II CAPACITORS. The replacement of palladium for electrodesby cheaper metals or alloys requires the use of dielectrics with a low sintering temperature.We give the two following examples:

The addition of LiF or BaLiF3 to BaTi03 has made it possible to decrease the sinteringtemperature from 1400 to 930 ° C. The decrease of Tc (BaTi03

=393 K to a temperature

close to 300 K leads to very good electric performances (f[ (300 K) = 8300; tan &(300 K) =40 x 10~~). Multilayer capacitors of 3.20 x 2.40 x I-IS mm~ dimensions have been madewith such a dielectric: they reach a capacity of 162 nF with Ag-Pd electrodes with a high

concentration in silver [51, 52].

The addition of BaLiF3 to Pb(Fei/2Nbi/2)03 has made it possible to decrease the Curietemperature of the latter (Tc

=387 K) to room temperature and to sinter ceramics at

temperature lower than 900 ° C. Figure 12 shows that the values of e[ are very strong; thethermal dependence of e[ means that such dielectrics may be put in the ZSU class [53].


10~~.E~i #

~~ E',(2g 310~.,E1(293 K)

~~zsu"

I20'

0

I

-56~

358 T(K)i o

283 29

>, '

~ j~)~ ~-j(~ 3°°

Fig. 12. Temperature dependence off) for an oxyfluoride ceramic derived from Pb(Fei/2Nbi/2)03.

The addition of both LiF and L12 C03 makes it possible to sinter ceramics of Pb(Mgi /3Nb2 /303 [PMN] at 850 ° C avoiding in addition the parasite formation of the pyrochlore phase [54].

5.3. CRYSTALS FOR ELECTRO- OPTIC APPLICATIONS. Crystal growth studies are in progresson ferroelectric fluorides with a view to electro-optic applications due in particular to the good

transparency of fluoride crystals.

6. Discussion Conclusion

Fluoride and oxyfluoride ferroelectrics constitute a group of new materials. Although the metal-fluorine bonds lead to a strongly ionic character, their crystalline networks show distortions

capable of leading to ferroelectrics of displacive or order-disorder type. The Curie temperature

may be very high; for example, the phases of BaMF4 type are ferroelectric up to their melting

temperature. There are now large families in which the value of Tc may be related to thesize and the electronic configuration of the various cations, and to the MX (X = O, F) bondcovalency. Ferroelectricity in fluorides and oxyfluorides has been predicted from very precise

structural studies [55].The following results are to be noted. The Pb5A13F19 compound has a very rich transition

sequence with various ferroic properties: ferroelectricity, antiferroelectricity, ferroelasticity.The fluorine K3Fe5F15 of "bronze" type constitutes a very original example. In fact, thecorresponding oxides are ferroelectric and a low F-O substitution rate (F IO +J 1/15) generally

causes the disappearance of the spontaneous polarization; the very distorted M06 octahedraleads to non-distorted M(O, F)6 ones, the M"+ cation being localized at the octahedron center.


In the case of the K3Fe5F15 fluoride, it is the simultaneous presence of Fe~+ and Fe3+ whichleads to an ordered arrangement giving rise to local dipolar moments in octahedra and thusto a spontaneous polarization. This material fully deserves its "bronzes" designation as is the

case for the Ko 57iV03 oxide type which also has tungsten in the two oxidized states +V and+VI. The oxyfluoride Na5W30gF5 is the leading member of an important family of materials;their good quality and large crystals make them potential candidates for applications.

The progressive F-O substitution from ferroelectric oxides with octahedra linked by cornershas the advantage for modulating the value of Tc, and thus the value of the permittivity at thedesired temperature; in addition, it makes it possible to densify ceramics at low temperature.

Moreover, the good transparency of fluorides means that the corresponding crystals have apotential value for electro-optic applications.

References

[ii Ravez J., Non linear properties of fluorides, Inorg. Solid Flttorides, Acad Press (1985) 469[2j Edwardson P-J-, Boyer L-L

,

Newman R-L-, Fox D.H., Hardy J-R-, Flocken J.W., GuentherR-A- and Mei W., Ferroelectricity

inperovskitelike NaCaF3 Predicted ah imtio, Phys. Rev.

B 39 (1989) 9738.

[3j Pepinsky R. and Jona F., New ferroelectric crystal containing no oxygen, Phys. Rev. 105(1957) 344.

[4] Eibschfitz M., Guggenheim H-G-, Wemple S-H-, Camlibel I. and DiDomenico M., Ferro-electricity in BaM~+F4, Phys Letters 29A (1969) 409.

[5] Abrahams S.C., Ravez J., Simon A. and Chaminade J.P., Ferroelectric behavior and phasetransition at 715 K in SrAlF5, J. Appt. Phys. 52 (1981) 4740.

[6] Ravez J., Andriamampianina V., Simon A., Grannec J. and Abrahams S-C-, Correlationbetween Curie temperature and cation radius in the ferroelectric BaFeF5 family, Ferro-electrics. 109 (1990) 33

[7] Tressaud A., Lozano L, and Ravez J., A cell for dielectric measurements in fluorinatedatmospheres, J. Flttor. Chem. 19 (1981) 61.

[8] Ravez J., Abrahams S.C. and de Pape R., Ferroelectric-ferroelastic properties of K3Fe5 Fiband the phase transition at 490 K, J. Appt. Phys. 65 (1989) 3987.

[9] Abrahams S-C-, Albertsson J., Svensson C. and Ravez J., Structure of Pb5Cr3F19 at295 K, polarization reversal and the 555 K phase transition, Acta Cryst. B 46 (1990) 497.

[10] Peraudeau G., Ravez J. et Arend H., #tude des transitions de phases des compos6sRb2KM03F3, CS2KMO~F3 et Cs2RbM03F3 (M

=Mo, W), Solid State Commttn. 27

(1978) 515.ill] Peraudeau G., Ravez J., Hagenmuller P. and Arend H., Study of phase transition in

A~M03F~ compounds (A=

K, Rb, Cs; M=

Mo, W), Solid State Commttn. 27 (1978)591.

[12] Chaminade J-P-, Cervera-Marzal M. and Ravez J., Na3W03F31 a new ferroelastic-ferroelectric oxyfluoride, Mat. Sc. Engm. B 3 (1989) 497.

[13] I8mailzade1-H- and Ravez J., B12Ti04F2. A new one-layer perovskite-like ferroelectric,Ferroelectrics 21 (1978) 423.

[14j Doumerc J-P-, Elaatmani M., Ravez J., Pouchard M. et Hagenmuller P., Les transitionsde phases de Na5W30gF5, Solid State Commttn. 32 (1979) iii.

[15] Ravez J., Elaatmani M. et Hagenmuller P., Influence de divers types de substitution surles temp6ratures de transition des oxyfluomres ferroAlectriques de type chiolite, Mat. Res.Bttll. 16 (1981) 1253.


[16] Arquis S., Ravez J., Chaminade J-P-, Hagenmuller P,

Abrahams S-C- and Marsh P., Phasetransition and ferroelectric behavior in Pb5M30gFjo (M

=Mo, W) and phase transition

in Pb5T1303F16, J. Appt. Phys. 60 (1986) 357.[17] Agulyansky A-I-, Ravez J., von der Mfihll R. and Simon A., Piezoelectricity and pyroelec-

tricity in A5Nb30F18, Ferroelectrics158 (1994) 139.[18j Bither T-A- and Young H-S-, Nitrato- and fluoboracites M3B7013N03 and M3B7013F,

J. Solid State Chem. 10 (1974) 302.[19] Hoshino S., Vedam K., Okaya Y. and Pepinsky R., Dielectric and thermal study of

(NH4)2S04 and (NH4)2BeF4 transitions, Phys. Rev. l12 (1958) 405.[20] Ravez J., Pouchard M. and Hagenmuller P., Chemical bonding and ferroelectric per-

ovskites, Ettr. J. Solid State Inorg. Chem. 28 (1991) l107.[21] Ravez J., Abrahams S-C-, Simon A., Calage Y. and de Pape R., The first ferroelectric

fluoride with a tungsten bronze-type structure, Ferroelectrics 108 (1990) 91.[22] Ravez J., Abrahams S-C-, Mercier A-M-, Rabardel L. and de Pape R., Phase transition

dependence on composition in ferroelectric-ferroelastic K3-~Fe5F15 for 0 < x < 0.20,J. Appt. Phys. 67 (1990) 2681.

[23] Arquis S., Ravez J. and Abrahams S-C-, Phase transition at 555 K in non linear opticPb5Cr3F19, J. Appt. Cryst. 19 (1986) 374.

[24] Ravez J., Andriamampianina V., Simon A., Grannec J. and Abrahams S.C., Ferroelectric-paraelectric phase transition in Pb5M3F19 with M

=Al, Ti, V, Cr, Fe, Ga, J. Appt. Phys.

70 (1991) 1331.

[25] Ravez J., Andriamampianina V. and Abrahams S-C-, The ferroelectric, antiferroelectric,ferroelastic and paraelastic phases of Pb5A13Fig, Ferroelectrics 158 (1994) 133.

[26] Sarraute S., Ravez J., von der Mfihll R., Bravic G., Feigelson R-S- and Abrahams S-C-,Structure of ferroelectric Pb5A13F19 at 160 K, polarisation reversal and relationship toferroelectric Pb5Cr3F19, Acta Cryst. B 52 (1996) 72.

[27] Ravez J., La premibre phase monoclinique ferroAlastique de type A5M3Xig, C. R. Acad.SC. 317 (1993) 589.

[28] Ye Z-G-, Ravez J., Rivera J-P-, Chaminade J-P- and Schmid H., Optical and dielectricstudies of ferroelectric oxyfluoride K3Mo03F3 single crystals, Ferroelectrics 124 (1991)

281.

[29] Ravez J., Peraudeau G., Arend H., Abrahams S-C- and Hagenmuller P., A new family offerroelectric materials with composition A2B&f03F3 IA, B

=K, Rb, Cs for rA+ > rB+

and M=

Mo, W), Ferroelectrics 26 (1980) 767.[30] Lorient M., Tressaud A. et Ravez J., Les transitions de phases dans les systAmes

Rb3Mo03F3-Rb3FeF6 et (NH4)3FeF6-Rb3FeF6, Rev. Chim. Miner. 19 (1982) 128.

[31] Fouad M., Chaminade J-P-, Ravez J. et Hagenmuller P., Les transitions de phases desoxyfluorures A3TiOFS et A3M02F4 IA

=K, Rb, Cs; M

=Nb, Ta), Rev. Chim. Miner.

24 (1987) 1.[32] Chaminade J-P-, Cervera-Marzal M., Ravez J. and Hagenmuller P., Ferroelastic and fer-

roelectric behavior of the oxyfluoride Na3Mo03F3, Mat. Res. Bttll. 21 (1986) 1209.

[33] Ravez J., Elaatmani M. et Chaminade J-P-, Pr6paration, 6tudes optiques et d161ectriquesde monocristaux de Na5W30gF5, Solid State Commttn. 32 (1979) 749.

[34] Ihringer J., Abrahams S-C-, Prandl W., Ravez J. and Hewat A-W-, Structural study ofthe Na5W30gF5 Phase transitions by X-ray and neutron diffraction, Phase 7ransitions33 (1991) 69.

[35] Ravez J., Elaatmani M., Cervera-Marzal M., Chaminade J-P- et Pouchard M., Propr14t6scristallographiques et d161ectriques de deux nouvelles familles d'oxyfluorures contenant des

ions Li+ et K+ et de structure d6riv6e du type chiolite, Mat. Res. Bttll. 16 (1981) l167.


[36] Ravez J., Abrahams S.C., Marsh P., Arquis S and Chaminade J.P., Ferroelectric behaviorand phase transition at 785 K in Pb5W30gFio, Jpn. J. Appt. Phys. 24 (1985) 232.

[37] Ravez J., Les oxyfluorures ferroAlectriques en 1986, Rev. Chim. 23 (1986) 460.

[38] Cross L-E-, Relaxor ferroelectrics, Ferroelectrics 76 (1987) 241.

[39] Ravez J. et Simon A., Le premier relaxeur ferroAlectrique oxyfluorA, Phys. Stattts Sofidi159 (1997) 517.

[40] Elissalde C., Ravez J., Kazaoui S. and Etourneau J., High frequency dielectric relaxationin oxyfluoride perovskite ceramics, Mat. Sc. Engm. B15 (1992) 192.

[41] Guelin J., Ravez J. et Hagenmuller P., Nouvelles phases oxyfluorAes ferroAlectriques non-stcechiomAtriques dArivAes de LiNb03 et de LiTa03, J. Less Common Metals 137 (1988)

75.

[42] Ye Z-G-, von der Mfihll R. and Ravez J., New oxyfluorides and highly densified ceramicsrelated to LiNb03, J. Phys. Chem. Solids 50 (1989) 809.

[43] Ye Z-G-, von der Mfihll R. and Ravez J., Sintering mechanism of LiTa03 ceramics by theaddition of lithium and magnesium fluorides, Proc. IEEE Int. Symp. Appt. Ferroelectrics

(1991) 5'66.[44j Bush A-A- and Venevtsev Y-N-, Growth and certain properties of Pb5Ge3 IO, F)ii ferro-

electric crystals, Inorg. Mat. 17 (1981) 216.[45] Dune F-G- and Stemple N-R-, Ferroelectric properties of BaL12~A12-2zF4~04-4~, Phys.

Rev. 120 (1960) 1949.[46] Huang S-Y-, von der Mbhll R., Ravez J, and Hagenmuller P., Investigation of ferroelec-

tric and pyroelectric properties of ceramics with composition Ba(Li~~A12-2~)04-4~F4~(0 < a~ < 0.3), Proc. IEEE Int. Symp. Appt. Ferroelectrtcs (1992) 123.

[47] Huang S-Y-, von der Mbhll R., Ravez J. and Hagenmuller P., New ferroelectricBai-~Mz(L12zA12-2~)04-4~F4~ (M

=Pb, Sr), Proc. IEEE Int. Symp. Appt. Ferroelectrtcs

(1992) 360.[48] Campet G., Claverie J., Perigord M., Ravez J., Portier J. et Hagenmuller P., Sur de

nouvelles phases oxyfluorAes dArivAes du niobate de plomb Atudes cristallographiques etdiAlectriques, Mat. Res. Bttll. 9 (1974) 1589.

[49] Ravez J. and Baudry H., Dielectric properties of some oxyfluoride ceramics and thick films,Commun. at the "Fourth European Meeting on Ferroelectricity" (Portoroz, Yougoslavie,

1979).

[50] Campet G., Claverie J, Hagenmuller P. et Perigord M., CaractArisations Alectriques decouches minces isolantes d'oxydes et d'oxyfluorures dApos6s par pulvArisation cathodique,

Rev. Phys. Appt. 14 (1979) 415.[5 ii Beauger A., Lagrange A., Houttemane C. et Ravez J., Propr16t6s de d161ectriques ferro41ec-

triques oxyfluor6s. Application aux condensateurs c6ramiques multicouches, Proceeding ofthe International Conference on New Trends in Passive Compounds (Paris, 1982) p. 10.

[52] Desgardin G., Bajolet P., Raveau B. et Haussonne J., Le titanate de baryum en prAsence defluorure de lithium une nouvelle perovskite, Proceeding of the International Conference

on New Trends in Passive Compounds (Paris, 1982) p. 18.[53] Ravez J., Simon A., Rossignol J-F- et Hagenmuller P., Influence de l'addition de BaLiF3

sur les propriAt6s diAlectriques de Pb(Feo,5Nbo,5)03, Rev. Chim. Min. 22 (1985) 377.[54] Rossignol J-F-, Simon A., Ravez J. et Hagenmuller P., Propr16t6s d161ectriques de

cAramiques h base de Pb(Mgi/~Nb2/3)03 frittAes h basse tempArature grhce h l'ajoutdu mAlange L12C03-LiF, Ann. Chim. FT. lo (1985) 21.

[55] Abrahams S-C and Ravez J., Dielectric and related properties of fluorine-octahedra fer-roelectrics, Ferroelectrics135 (1992) 21.

the inorganic fluoride and oxyfluoride ferroelectrics...j phys. iii ftance 7 (1997) 1129-1144 ju~ie...

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