High resolution x ray diffraction study of phase and domain structures and thermally induced phase transformations in PZN (4 5 9)%PT 4

Figure 5.6 Same as Figure 5.4b but after the fractured surface of PZN-7%PT crystal sample was polished with SiC papers of different particle sizes... After repeated polishing with care t

Figure 5.6 Same as Figure 5.4(b) but after the fractured surface of

PZN-7%PT crystal sample was polished with SiC papers of different particle sizes

tweed-like patterns (Figure 5.7c) After repeated polishing with care to remove a

sufficiently thick layer (>40 µm) from the surface of the sample, the surface domain

patterns as shown in Figure 5.7(a) persisted; and so was the presence of the broad

lower 2θ peak in the XRD profile These observations led us to believe that the

specific thin domain layer is related to the polished surface To check for this, a

PZN-4.5%PT sample, initially polished in the [100]pc direction (Figure 5.7a), was

tilted by an angle of 45° and again polished back and forth in the new direction After

the second polishing, the earlier set of domains disappeared and was replaced by a new

set of elongated domains aligned at an angle of about 30° towards the <110>pc

direction of polishing (Figure 5.7b) This confirms the observed domain patterns are

related to the polished surface We further confirmed that optically the polishing

induced surface domains can be reliably detected only if polishing direction was

roughly parallel to a certain crystallographic direction, e.g., [010]pc or [110]pc in our

experiments Otherwise, the domains are not evident and the sample is covered with

areas exhibiting slight but varying birefringence when observed under the crossed

polarizers (Figure 5.8) Despite the above, the lower 2θ peak is always present in the

x-ray profile following any direction of polishing, suggesting that the surface phase is

always present regardless of the direction and/or mode of polishing

This behavior can be explained in the following way If the polishing

Figure 5.7 Surface domain patterns of the (001)-cut PZN-4.5%PT crystal

plate (a) after polishing along the [010]pc direction and (b) after repolishing in the [110]pc direction Arrows indicate the direction

of polishing Note the realignment from (a) to (b) (c) The domain patterns in the underlying material revealed by the focusing technique

[100]

[010]

a

c

b

50 µm

[100]

[010]

50 µµµm

Figure 5.8 No clear surface domain patterns of (001)-cut PZN-4.5%PT

crystal plate as a result of none crystallographic polishing direction

direction changes in a non-coordinated manner, the directions of induced surface

stresses and domain directions are randomly distributed As the size of domains is very

small, they are not visible in the optical microscope In this case, since the surface

layer is composed of randomly oriented submicroscopic domains, the surface layer

does not exhibit a clear birefringent domain pattern In contrast, after directional

polishing the domains (and thus their optical indicatrix) are aligned into macroscopic

regions These regions are birefringent and can be identified under a polarizing

microscope

5.3.1 Thermal stability

The stability of the deformed surface layer was investigated by subjecting the

as-polished samples to different annealing treatments The heating and cooling rates

used were 1.5 ºC/min Figure 5.9 shows the (002) XRD profiles of the differently

annealed PZN-4.5%PT samples and the (002) XRD profile of the as-polished sample

After annealing for 1 h at 300 °C, the position of the lower 2θ peak shifted to 2θ ≈ 43.95° Subsequent annealing at 400 °C for 1 h did not produce significant change to

either the position or intensity of this peak The lower 2θ peak persisted even after

annealing at 600 °C for 5 h and the position shifted further to 2θ ≈ 44.05° (Figure 5.9)

2θ

as-polished 300oC (1h) 400oC (1h) 600oC (5h)

<002>R

~43.50o

~44.05o

~44.68o

Figure 5.9 (002) XRD profiles of as-polished (solid curve) and differently

annealed (dashed curves) PZN-4.5%PT showing the effects of the

different annealing treatments on the lower 2θ peak Sample

thickness is 1mm