Degree Of Compositional Order Research Articles

Phase transitions in PbYb1/2Nb1/2O3 with different degree of compositional ordering

Recently we found out that compositional ordering degree s of Yb3+ and Nb5+ ions in PbYb1/2Nb1/2O3 (PYN) ceramics can be varied by means of high-energy mechanical activation. In the present work dielectric and X-ray diffraction studies of the three obtained PYN ceramic samples with differing s values have been carried out in a wide temperature range. The highly disordered (s ≈ 0) sample appeared to be cubic in the 20–350 °C range and exhibited a diffused and frequency-dependent permittivity maximum at Tm ≈ 80 °C. Samples with s = 0.69 and 0.82 were orthorhombic at room temperature and exhibited non-diffused and frequency-independent permittivity maximum at Tm ≈ 170 and 250 °C respectively. However even in the most ordered PYN sample (s ≈ 0.82) cubic paraelectric and orthorhombic antiferroelectric phases coexist in the 190–300 °C temperature range.

Control of the degree of compositional ordering of Pb2YbMO6 (M – Nb, Ta) perovskites by means of mechanical activation

ABSTRACTIt has been found out that compositional ordering degree of the Yb3+ and M5+ (M – Nb, Ta) ions in Pb2YbМO6 ceramics and, correspondingly, both temperature and diffusion of antiferroelectric phase transition can be varied within a wide range by means of high-energy mechanical activation. In particular, disordered modifications of Pb2YbМO6 (M – Nb, Ta) were obtained without using any additives for the first time.

Structural, dielectric and Mossbauer studies of PbFe0.5Sb0.5O3 ceramics with differing degree of compositional ordering

ABSTRACTCeramic samples of a new perovskite multiferroic PbFe0.5Sb0.5O3 (PFS) with a differing degree S of long-range compositional ordering of the Fe3+ and Sb5+ cations were fabricated by a variation of the high-pressure-synthesis conditions. The S values estimated from the XRD data varied from 0.93 down to 0.17. The unit cell parameter was found to decrease with increasing S. In line with these results the fraction of the singlet component in the Mössbauer spectra was found to decrease with decreasing S. However, the temperatures and diffusion of dielectric permittivity maxima as well as the temperature of magnetic phase transition determined from Mössbauer data do not change substantially with S. These results imply that PFS remains highly ordered at the nanoscale.

X-ray and dielectric studies of liquid-phase sintered PBB1/2 3+B1/2 5+O3 ceramics with differing degree of compositional ordering

Ceramics of several PbB1/2 3+ B1/2 5+O3 perovskites (B3+-In, Sc, Yb, Lu, Er, Tm; B5+-Nb, Ta) with differing degree of compositional ordering were obtained using Li2CO3 additions. Ordering process in Li-doped ceramics is greatly enhanced due to recrystallization of grains in the presence of liquid phase. The properties of Li—doped ceramics are similar to those of crystals grown from the flux at the same temperatures. In some of the perovskites studied compositional order-disorder phase transitions and the transformation of antiferroelectric phase transition into ferroelectric one were observed.

Concentration dependence of the compositional order-disorder phase-transition temperature in the solid solution PbSc0.5Nb0.5O3-PbSc0.5Ta0.5O3

The degree of compositional order S of crystals of the complete series of solid solutions (1−x)PbSc0.5Nb0.5O3-xPbSc0.5Ta0.5O3 grown under identical conditions is determined by x-ray examination. The form of the dependence S(x) and the variations of S for different compositions, after high-temperature annealing, indicate that the concentration dependence of the compositional order-disorder phase-transition temperature is close to linear in the given system of solid solutions.

Ordered structures in SixGe1-x alloy thin films.

Compositional ordering in Si{sub 0.5}Ge{sub 0.5} alloy films grown epitaxially on Si(001) substrates was investigated using four-circle x-ray-diffraction measurements. Thin-film alloy samples grown by molecular-beam epitaxy, as well as a sample grown by pulsed chemical vapor deposition were studied, and half-integral reflections, indicating a doubling of the conventional cubic unit cell, were observed in all samples. Quantitative structure factors measured in absolute units were compared with proposed structural models to extract the atomic structure and degree of compositional ordering. The measurements are consistent with the predictions of a bilayer step-flow growth model in which ordering results from atomic segregation at specific kink sites. In addition to the half-integral reflections, weak integral {ital hkl} reflections, which are forbidden for the diamond structure, were also observed. These reflections are attributed to the presence of a secondary ordered structure similar to CuAu-I, with a superlattice periodicity along the in-plane [100] direction.

Dielectric properties and diffusion of ferroelectric phase transition in lead indium niobate

Abstract Temperature dependences of dielectric permittivity and tanδ in PbIn0.5Nb0.5O3 crystals where the degree of compositional order was changed by annealing at 400–1050 °C and subsequent cooling at different rates are determined. In these crystals the diffuse phase transition from paraelectric to ferroelectric phase is accompanied by the tanδ increase. In the vinicity of the transition between para- and antiferroelectric phases there exist no tanδ anomalies. Such anomalies may serve as a criterion allowing to distinguish ferro- and antiferroelectric transitions. The degree of ferroelectric transition diffusion depends on the cooling rate after annealing: the lower the rate, the higher the diffusion.