J. F. Meng

Grain size effect on ferroelectric phase transition in Pb1 − xBaxTiO3 ceramics

Abstract Micro-Raman scattering measurements in the frequency range of 5–1000 cm −1 as well as X-ray diffraction have been carried out on nanocrystalline Pb 1 − x Ba x TiO 3 system. A grain size and Ba ion-induced phase transition from the tetragonal ferroelectric phase of PbTiO 3 to the cubic paraelectric phase of BaTiO 3 is found to occur at x ~0.7 and it is associated with the “softening” of the mode at 74 cm −1 ( x = O ) which arises from a delicate balance between long-range Coulomb forces and short-range repulsion. A lowest frequency phonon mode at 10 cm −1 is detected and its grain size, Ba composition and temperature dependence appears to be correlated with structures for ABO 3 oxides. The temperature dependence of Raman phonon modes for Pb 0.6 6Ba 0.4 TiO 3 with grain size of 60 nm reveals a temperature-induced soft mode phase transition occurring at 360K.

Study of visible emission and phase transition in nanocrystalline A1−xA′xTiO3 systems

Abstract Room temperature photoluminescence spectra on Ba 1− x Pb x TiO 3 and Sr 1− x Pb x TiO 3 , with grain sizes of ∼ 60 and ∼ 30 nm, respectively, have been measured. The Pb content dependence of the visible emission can be used to provide evidence for the origin of photoluminescence occuring in these nanocrystalline ABO 3 oxides. The phase transitions for Ba 1− x Pb x TiO 3 and Sr 1− x Pb x TiO 3 are found to have an obvious effect on the visible emission band.

Raman investigation on (Ta2O5)1−x(TiO2)x system at different temperatures and pressures

Abstract Micro Raman spectra for (Ta2O5)1−x(TiO2)x reveal an induced Raman enhancement of the low frequency phonon modes for a critical TiO2 content, x = 0.08. The temperature and pressure effects on these modes have also been studied. The Raman enhancement is shown to be associated with effects of the superstructure which is composed of TiO6 octahedra and Ta-O clusters. Pressure Raman scattering on (Ta2O5)0.92(TiO2)0.08 indicates that a phase transition occurs at ~6.22 Gpa. Based on our Raman scattering studies, the origin responsible for the enhanced dielectric constant in samples with TiO2, content, x = 0.08, has been provided and discussed.

Low frequency phonon modes and ferroelectric phase transitions in nanocrystalline Pb1−x A x Ti1−y B y O3

Abstract Low frequency Micro-Raman scattering measurements as well as X-ray diffraction have been carried out on nanocrystalline PbZr1−y TiyO3, Pb1−x Sr x TiO3, Pb1−x LaxTiO3 and Pb1−x Ba x TiO3 system. Grain sizes-induced and different doping ions-induced phase transitions from the tetragonal ferroelectric phase to the cubic paraelectric phase were identified in these ABO3 systems. These phase transitions are closely concerned with the “softening” of the low frequency phonon modes. A lowest frequency phonon mode at 10c−1 is detected. The temperature dependence of Raman phonon modes for Pb0.8La0.2TiO3 with grain size of 58nm reveals a temperature-induced soft mode phase transition occurring at 375K. The “softening” of the low frequency modes with reducing grain size and increasing doping ion content and temperature is shown to arise from a delicate balance between long-range Coulomb forces and short-range repulsion. Investigations show that PbTiO3 has an adjustable Curie temperature depending on different...

Grain size effect on ferroelectric phase transitions in nano-crystalline perovskite materials

Abstract The effects of grain size on the ferroelectric transition temperature in nano-crystalline complex ferroelectric perovskite oxides, have been investigated employing micro-Raman scattering spectroscopy as a function of temperature and pressure. There appears a distinct soft mode induced phase transition in each sample and the transition temperature decreases with decreasing grain size. For example, the observed soft mode Raman frequency in pure PbTiO3, with grain size of 60 nm, remarkably shifts to lower frequency relative to single-crystal, powder or thin film data, clearly indicating a lowering in its transition temperature. Grain size-induced phase transformation from ferroelectric tetragonal to paraelectric cubic phase in nano-crystalline Pb1−x BaxTiO3, is found to occur at x=0.7 and it is associated with the Ba concentration dependence ofthe soft mode. These studies show possibility of preparing high efficiency PbTiO3 sensors that can be operated close to ambient temperature.

Photoluminescence in PbMg1/3Nb2/3O3–PbIn1/2Nb1/2O3 systems

Photoluminescence for PbMg{sub 1/3}Nb{sub 2/3}O{sub 3} (PMN){endash}PbIn{sub 1/2}Nb{sub 1/2}O{sub 3} (PIN) solid solutions in the temperature ranging from 35 to 295 K have been obtained for the first time. An abrupt photoluminescence enhancement of the system has been observed to occur at {approximately}210 K, which can be attributed to the growing and merging of dynamic polar microregions or to the phase transformation of the material at this temperature. The PIN content has been found to affect the photoluminescence of the PMN-PIN system significantly. The photoluminescence mechanism for PMN-PIN has been studied. {copyright} {ital 1998 Materials Research Society.}

Effect of grain size and Pb dopant on luminescence in BaTiO3

Photoluminescence spectra of Ba1−xPbxTiO3 with grain sizes of 60 nm have been obtained. Different emission bands for pure BaTiO3 have been separately obtained against two excitation lines of 488.0 and 514.5 nm. Based on the dependence of the visible emission band upon Pb content and excitation power, a model that describes the origin of visible emission has been suggested.Photoluminescence spectra of Ba1−xPbxTiO3 with grain sizes of 60 nm have been obtained. Different emission bands for pure BaTiO3 have been separately obtained against two excitation lines of 488.0 and 514.5 nm. Based on the dependence of the visible emission band upon Pb content and excitation power, a model that describes the origin of visible emission has been suggested.

Visible emission study in nanocrystalline Ba1-xPbxTiO3 and Sr1-xPbxTiO3 systems

Abstract Photoluminescence spectroscopy measurements., on Ba1−xPbxTiO3 and Sr1−xPbxTiO3, and with grain sizes of 60 and 30 nm respectively, have been carried out. A single-emission band at ~ 2.0 eV for pure BaTiO3 and at ~ 2.14 eV in the case of pure SrTiO3, had been observed at room temperature. The dependences of the band-position, -intensity, and -width of the visible emission on Pb concentration using the excitation line of 514.5, has been studied and offered a model responsible for the origin of photoluminescence in nanocrystalline BaTiO3 and SrTiO3. The thermal quenching of photoluminescence for pure bulk materials has been discussed.

Effect of doped ions on soft mode and phase transitions in Bi layered compound

Abstract Raman spectra of Bi2-xAxTi4-yByO11(A = Gd, Yb, La, Nd, Sb, Fe; B = Te, Zr, Sn) have been systematically investigated. The results show that these doped ions have different effects on the lowest frequency phonon mode (soft mode) and the phase transition in Bi2Ti4O11. The phase transitions in Bi2-xAxTi4O11 system is directly associated with softening of the lowest frequency phonon mode, which results from the changes in the short-range forces. Temperature, pressure and doped ion concentration - induced phase transition is separately correlated with an unstable displacement of Bi ions with a charge transfer effect in Bi-O-Ti system. The softening and normal behavior observed can be explained as due to the effects of local distortion on Bi ion displacement. The non-zero soft mode frequency at the phase transition may come from a coupling between the soft mode and an additional phonon mode.