Morphotropic

Morphium, n. morphine, morphotropisch, a. morphotropic. morsch, a. rotten, decayed tender, fragile, morschen, v.u rot, decay. 

However, a giant piezoelectric effect has been found in the Pb-based complex pervoskite oxides. In particular, the morphotropic boundary relaxor and PbTio3 complex exhibits huge piezoelectric response, so that an effective piezolysis is expected. 

Fig. 9.4. Dependence of piezoelectric properties of PbZrOj-PbTiOj on composition. The zirconate-rich phase is rhombohedral, whereas the titanate-rich phase is tetrahedral. The piezoelectric coefficients reach a maximum near the morphotropic phase boundary, approximately 45% PbZrOj and 55% PbTiOj. (After Jaffe et al., 1954.)...

Figure 1.13 Phase diagram for PZT showing the morphotropic phase boundary between rhom-bohedral and tetragonal phases.

Analogous C(V) curves were recorded on pzt bulk ceramics with compositions around the morphotropic phase boundary (mpb). Figure 1.25 displays the relative permittivity as a function of DC-bias for a tetragonal (x = 0.48), a morphotropic (x = 0.52) and a rhombohedral (.x = 0.58) sample. In contrast to thin films additional humps observed in the e E) curves. This could be explained by different coercive fields for 180° and non-180° domains [31]. Their absence in ferroelectric thin films could be taken as evidence for suppressed non-180° domain switching in thin films [30],... 

Figure 2.4 Strain-field curves for < 001 > oriented 0.91PbZn1/3Nb2/303-0.09PbTi03 single crystals. The sample in (a) was poled at room temperature, where the resulting domain state is unstable (due to induction of tetragonal material associated with the curved morphotropic phase boundary), yielding substantial hysteresis. In (b) the crystal was poled at low temperatures to keep it in the rhombohedral phase. When measured at room temperature, the piezoelectric response is much more linear and non-hysteretic, due to the improved stability of the ferroelectric domain state. Data courtesy of S. E. Park.

The present work summarizes opportunities of using high-resolution synchrotron and standard xrd techniques for structural characterization as well as for investigations of structure-property-relationships. xrd will be used to determine quantitatively the phase content of morphotropic pzt. Temperature dependent measurements provide information about the phase transformation of morphotropic donor doped pzt ceramics and high-resolution synchrotron X-ray diffraction gives information about the extrinsic and intrinsic contributions to the electric field induced strain, xrd results are finally compared with electrical measurements to analyze the interactions among microstructure, phase content and properties. 

Figure 7.1 Typical XRD spectra of a morphotropic pzt ceramic with the corresponding peaks of the tetragonal (Fr) and rhombohedral (Fr) phase.

The replacement of zirconium by isovalent hafnium has little effect apart from shifting the morphotropic boundary (see Fig. 6.7) to 52mol.% PbTi03. Replacement by tin causes a slight loss in piezoelectric activity, shifts the morphotropic boundary to 42 mol. % PbTi03 and lowers the Curie point from 370 to 250 °C. 

The isovalent A-site substituents barium, strontium and calcium lower the Curie point and have a small influence on the morphotropic composition. At the 5-10 mol.% level they enhance the permittivity and piezoelectric properties. Pb0 94Sr0 06Ti0 47Zr0 53 for instance has a relative permittivity of 1300, a kp of 0.58... 

The system now shows two morphotropic phase boundaries, the one already discussed on the PZ-PT join, and the other on the PT-Pb(B B")03 join. Compositions close to that of the MPB (II) have attracted considerable interest because of their potential for electromechanical applications. The properties of some selected systems are given in Table 6.2 together with those for the PZT system for comparison. 

The substitution of lead by barium enhances the piezoelectric properties which peak when Pb/Ba I. At this and higher barium contents the structure changes to tetragonal with the polar axis parallel to the A-site tunnels. There is a morphotropic boundary, similar to that found in PZT compositions, and peak values of piezoelectric properties are found near the Pb1/2Ba1/2Nb206 composition. d33 rises to 220 pCN-1 and d31 rises to — 90pCN 1, while Qm increases to 300 and the Curie point falls to 250 °C thus most of the features peculiar to... 

Eitel, R.E. et al. (2001) New high temperature morphotropic phase boundary piezoelectrics based on Bi(Me)03-PbTi03 ceramics, Jpn. J. Appl. Phys., 40, 5999-6002. 

Zhang H, Leppavuori S, Karjalainen P (1995) Raman spectra in laser ablated lead zirconate titanate thin films near the morphotropic phase boundary. J Appl Phys 77 2691 Ching-Prado E, Cordero J, Katiyar RS, Bhalla AS (1996) Temperature-dependent Raman scattering in PT and PMN-PT thin films. J Vac Sci Technol A 14 762... 

Nalbandyan, V.B., and Shukaev, I.L., New modification of lithium ferrite and the morphotropic series AFe02, Russ. J. Inorg. Chem., 32, 808, 1987. 

The data collected unambiguously indicate the existence of a large variety of actinide orthophosphates and their analogues (orthovanadates, orthoarsenates, orthosilicates, etc.). They are characterized by iso- and heterovalent isomorphic substitutions of cations and anions, and polymorphic and morphotropic transitions. The data analysis allows to predict many new actinide compounds of the group with different expected stmctures and tailored properties, including stability in different extreme physical fields and chemical media. Certain progress in this research direction has already been achieved. 

K-Rb-Cs leucite. The much-studied feldspathoid leucite (KAlSi206) provides an example of the close correspondence between polymorphic and morphotropic displacive transitions. Leucite readily accommodates substitutions of its alkali cation, and... 

Nevertheless, the analogies between morphotropic and polymorphic transitions in leucite are not exact. Palmer et al. (1989, 1997) calculate a total spontaneous strain (stot) produced by the transition, and they subdivide this total strain into a nonsymmetrybreaking volume strain (Sa) and a symmetry-breaking ferroelastic strain (se) using the relations ... 

In short, K-leucite and its Rb- and Cs-derivatives nicely demonstrate a general rule concerning polymorphic and morphotropic transitions for a given mineral system The similarities are striking, but observations based on one transition mechanism are not automatically transferrable to the other. 

PRINCIPLES OF MORPHOTROPIC TRANSITIONS Types of atomic substitutions... 

Figure 6. Schematic representations of morphotropic phase diagrams.

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