Raman spectroscopy of radiation-damaged natural zircon samples shows increased line broadening and shifts of phonon frequencies with increasing radiation dose. Stretching and bending frequencies of SiO 4 tetrahedra soften dramatically with increasing radiation damage. The frequency shifts can be used to determine the degree of radiation damage. Broad spectral bands related to Si-O stretching vibrations between 900 and 1000 cm −1 were observed in metamict/amorphous zircon. The radiation-dose-independent spectral profiles and the coexistence of this broad background and relative sharp Raman modes in partially damaged samples indicate that these bands are correlated with amorphous domains in zircon. The spectral profiles of metamict zircon suggest that in comparison with silica, the SiO 4 tetrahedra are less polymerized in metamict zircon. This study also shows that ZrO 2 and SiO 2 are not the principal products of metamictization in zircon. No indication of bulk chemical unmixing of zircon into ZrO 2 and SiO 2 was found in 26 samples with a large variation of radiation damage (maximum dose: 23.5 × 10 18 α-events g −1). Only one sample showed clearly, in all measured sample areas, extra sharp lines at 146, 260, 312, 460 and 642 cm −1 characteristic of tetragonal ZrO 2. The geological (and possibly artificial heating) history of this sample is not known. It is concluded that radiation damage without subsequent high temperature annealing does not cause unmixing of zircon into constituent oxides.

The behavior of the Pm3m-R3c phase transition in LaAlO 3 ͑T C = 813 K from differential scanning calorimetry measurements͒ has been studied using temperature-dependent measurements of the crystal structure, dielectric relaxation, specific heat, birefringence, and the frequencies of the two soft modes ͑via Raman spectroscopy͒. While all these experiments show behavior near T C consistent with a second-order Landau transition, there is extensive evidence for additional anomalous behavior below 730 K. Below this temperature, the two soft mode frequencies are not proportional to each other, the spontaneous strain is not proportional to the square of the AlO 6 rotation angle, and anomalies are seen in the birefringence. Twin domains, which are mobile above 730 K, are frozen below 730 K. These anomalies are consistent with biquadratic coupling between the primary order parameter of the transition ͑AlO 6 rotation͒ and a second process. From the dielectric results, which indicate a smooth but rapid increase in conductivity in the temperature range 500-800 K, we propose that this second process is hopping of intrinsic oxygen vacancies. These vacancies are essentially static below 730 K and dynamically disordered above 730 K. The interaction between static vacancies and the displacive phase transition is unfavorable. A similar anomaly may be observed in other aluminate perovskites undergoing the same transition.

Recrystallization and structural recovery in α-decay damage in zircon samples have been studied using Raman spectroscopy. Fifteen zircon samples with different degrees of radiation damage have been thermally annealed between 600 K and 1800 K for up to 28 days and 8 hours. The experimental results from this study reveal that recrystallization in the damaged zircon samples is a multi-stage process that depends on the degree of initial damage of the samples. In partially damaged samples the lattice recovery of damaged crystalline ZrSiO 4 takes place at temperatures as low as about 700 K, as shown by a remarkable band-sharpening and a significant increase in the frequencies of ν 1 and ν 3 Si-O stretching vibrations together with the external band near 357 cm −1 with increasing temperature. A dramatic increase of Raman scattering intensity of ZrSiO 4 occurs in partially damaged samples near 1000 K due to a recrystallization process involving epitaxial growth. Heavily damaged samples tend to decompose into ZrO 2 and SiO 2 at high temperatures. Tetragonal ZrO 2 has been observed under annealing between 1125 K and about 1600 K in heavily damaged samples while monoclinic ZrO 2 appears above 1600 K. Weak signals from ZrSiO 4 were detected at 1125 K in highly metamict zircon although the main recrystallization appears to occur near 1500 K accompanied by a decrease of the volumes of ZrO 2 as well as SiO 2. This suggests that this recrystallization is associated with the reaction of ZrO 2 with SiO 2 to form ZrSiO 4. A possible intermediate phase has been observed, for the first time, by Raman spectroscopy in damaged zircons annealed at temperatures between 800 K and 1400 K. This phase is characterized by strong, broad Raman signals near 670, 798 and 1175 cm −1. Prolonged isothermal annealing at 1050 K results in a decrease of these characteristic bands and eventually the disappearance of this intermediate phase.

Elastic, piezoelectric, and dielectric properties of Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 Pb-free ceramic at the morphotropic phase boundary

We show that lead zirconate titanate thin films undergo local phase decomposition during fatigue. The original remanent polarization of the fatigued film is completely restored after furnace annealing in an O2 atmosphere, following a significant regrowth of a perovskite phase from the pyrochlorelike structure. By comparing our data with other researchers' work on annealing of fatigued ferroelectric samples, we conclude that local phase separation is the generic reason for electrical fatigue in ferroelectrics. A fatigue model is proposed in order to interpret our experimental data.

Following our recent experimental work on electrical fatigue ͓Phys. Rev. Lett. 97, 177601 ͑2006͔͒, a theory of a charge-injection fatigue model is developed, emphasizing the extremely high depolarization electric field generated near the electrodes by bound charges at the tip of needlelike domains during switching. In particular, the relationship P r ͑N͒ / P r ͑0͒ϳexp͑−N / ͒, where N is the number of the fatigue cycles and ӷ1, is derived, which explains the statistical origin of the universality of the logarithmic fatigue behavior observed for various ferroelectric substances in the literature. The consistency of this model with extensive body of the experimental data has been discussed and a systematic picture of fatigue is established. In particular, the "size effect"/fatigue coupling, the fatigue-free behavior of low P r samples, and the exaggerated fatigue data of Colla et al. ͓Appl. Phys. Lett. 72, 2478 ͑1998͔͒ at very low frequencies ͑mHz͒ are all well predicted by our model.

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Zircon- and reidite-type ZrSiO4 produced by shock recovery experiments at different pressures have been studied using infrared (IR) and Raman spectroscopy. The v3 vibration of the SiO4 group in shocked natural zircon shows a spectral change similar to that seen in radiation-damaged zircon: a decrease in frequency and increase in linewidth. The observation could imply a possible similar defective crystal structure between the damaged and shocked zircon. The shock-pressure-induced structural phase transition from zircon (I41/amd) to reidite (I41/a) is proven by the occurrence of additional IR and Raman bands. Although the SiO4 groups in both zircon- and reidite-ZrSiO4 are isolated, the more condensed scheelite gives rise to Si–O stretching bands at lower frequencies, suggesting a weakening of the bond strength. Low-temperature IR data of the reidite-type ZrSiO4 show an insignificant effect of cooling on the phonon modes, suggesting that the structural response of reidite to cooling-induced compression is weak and its thermal expansion is very small.