© Elsevier,Paris Properties of perovskite ferroelectrics Ann. Chim. ScL Mat, 2001, 26, pp. 99-106 PIEZOELECTRIC PROPERTIES OF PEROVSKITE FERROELECTRICS: UNSOLVED PROBLEMS AND FUTURE RESEARCH Dragan DAMJANOVIC Ceramics Lab~atcfy, Mate~ds Department, SwissFederal Institute of Technology- EPFL, 1015 Lausanne, Switzerland Abstract - This article reviews recent advances in the studies of the piezoelectric prope~es of txax3vsldte matexials. Pefovskite compositions are the best known and the largest family of fet'roelectric and piezoelectric materials. The deixmdetr~ of the longitudinal, d33, piezoelectric coefficient on crystallographic orientation was examined in single crystals of BaTiO~, PbTiO3, Pb(Zr,Ti)O3, K N t ~ , relaxor-ferroelectric solid solutions [e.g. Pb(Mgv3Nbm)O3-PbTiO3 and Pb(ZnmNt~)Os-PbTiO3] and NamBiv2TiO3. In most cases the largest piezoelectric coeffficient was found in a direction which does not coincide with the polarization direction In relaxor fexrcelectrics, some compositions near the morplmtropic phase boundary (MPB) exhibit very large piezoelectric (>2000 pC/N) and coupling coefficients (k33>90%). results are discussed in terms of so-called en#ne~'ed domain structure and crystal anisotropy. The article also discusses evidence for the presence of a monocUnic phase bOween the rhombohedral and tetragonal phases at the MPB in Pb(Zr, Ti)O~. R~sun~ - Propri~t~s pi~zo-~ectriques des perovskltes ferro(dectrlques : problbmes non r~solus et recherches futures. Cet article rccense l'avancemem des travaux Ics plus r~mts sur les propri(~s pi~zo- ~lectriques des math'iaux pexovskites. Les compos~ perovskites forment la plus gramle famille de mat&iaux f~o~lectriques et pi~zo-~lectriques et ils sont dgalement les mienx connus. Rh:Amunent, la variation du coefficient pi~Mlectrique longitudinal, (133,en fonction de rodentation cristallographique a 6tudi6e dar~ des monocristaux de BaTiOj, PbTiO3, PbCZr,Ti)O3, KNbO3, des solutions solides de relaxeurs fea'ro~lectriques [e. g. Pb(Mgv3Nbm)O3-PbTiO3 et Pb(ZnvvNb2t3)O3-PbTiO3] et NamBiv2TiO3. Dam la plupart des cas, le coefficient pi~zo~lectrique le plus important a (~6 tronv6 dans une direction ne COinCidant pas avec la direction de polarisation. Cextaines compositions, pour les relaxeurs fexro~lectriques, voisines de la phase mcrphotroplque montrent un coefficient pi(~3~lectrique d33 (>2000 pC/N) et un coefficient de conplage k33 (>90%) exgr~.lnelileAltiinpcgtan~. CeS rdsultats sont discut~s ca tennes de structure de domaines, cr(~s par le champ ~ectrlque, et d'anisotropie c~talli.e. L'article examine dgalement, dam le domaine do comix)sition mcrphotroplque de Pb(Zr, Ti)O3, la pr(~ce possible d'une phase monoclinique s'intvrcalant entre les phases quadratique et rho~que. I. INTRODUCTION The perovskitc comix~itions arc the most important class of ferroelectric mate~als. The general formula is ABO3 wh~e cation A has a valence +1, +2, or +3 and B has a valence from +3 to +6 [1]. The basic building block of the perovskite structure is the oxygen ~ o n , BO6, where B ions occupy the octahedxal intexstice, oxygen ions O are shared by neighboring octahedra, and A ions are packed in the space between Reprints: Dragan Damjanovic, DMX-LC, EPFL, 1015 Lausanne, Switzexland