Structural and dielectric study of the Na0.5Bi0.5TiO3–PbTiO3 and K0.5Bi0.5TiO3–PbTiO3 systems

Abstract

A study of the Na0.5Bi0.5TiO3-PbTiO3 and K0.5Bi0.5TiO3-PbTiO3 systems has been carried out using Xray diffraction, differential scanning calorimetry and dielectric measurements. The limits of the rhombohedral (Na0.5Bi0.5TiO3-rich side) and tetragonal (PbTiO3-rich side) solid solutions have been determined, as well as the evolution of their lattice parameters as a function of composition and temperature. Ceramic materials have been prepared by natural sintering (1090-1220 °C; 0.5 h) of powders obtained by solid-state reaction (900-1000°C; 20 h) of the corresponding oxides and carbonates. The dielectric permittivities of these materials have been measured in a wide frequency range for temperatures between 20 and 800 °C. The results showed that they all are ferroelectric at room temperature and exhibit either a diffuse, probably second-order phase transition, or a sharp, first order-like phase transition from the ferroelectric to the paraelectric state, depending on the composition.Lead titanate-zirconate ceramics (PZT) are currently the most used ferroelectric materials in the field of piezoelectric applications. A noticeable feature of these materials is the occurrence of a morphotropic phase boundary (MPB) in the phase diagram which separates tetragonal and rhombohedral ferroelectric regions. Solid solutions with compositions close to the MPB present the best electromechanical properties. In the research of new complex systems with interesting piezoelectric characteristics, care should be taken that thermal and time stability of the properties is connected with the value of the Curie temperature of the components. Previous works have shown that in most cases this corresponds to the situation where the MPB is located between tetragonal and rhombohedral phases. 1 Up to now, results concerning systems other than PZTs have only been devoted to either Na0.5Bi0.5TiO3-(Sr,Ba)TiO3 or the low-lead range of Na0.5Bi0.5TiO3-PbTiO3. [2][3][4][5][6] A study was therefore conducted on the whole Na0.5Bi0.5TiO3-PbTiO3 (NBT-PT) and K0.5Bi0.5TiO3-PbTiO3 (KBT-PT) systems, which are both likely to present MPBs. Actually, at room temperature NBT is rhombohedral (Tc  320 °C), KBT is tetragonal (Tc  380 °C) as is PT (Tc  490 °C). 7 This paper presents the results concerning the preparation of some materials belonging to this family as well as their thermal and dielectric properties.

Phase transition behaviors of (Na1/2Bi1/2)1−x TiPb x O3 thin films

“…As the composition of a phase boundary is largely dependent on the degree of lattice distortion of the solid solution end-members [6], the phase transition in NBPT(x) occurs on the sodium-rich side due to the relatively large lattice distortion of PbTiO 3 . This has been confirmed by earlier studies on NBPT(x) bulk ceramics [3,5,7,8]. However, there are several large discrepancies concerning the compositions of these phase transitions in the system.…”

“…For instance, although some investigators proposed the existence of a morphotropic phase boundary (MPB), very differing compositions (i.e., x=0.1, 0.13 and 0.13-0.15) have been reported for the MPB [3,7,8]. Moreover, Elkechai et al [5] suggested a biphasic region of 0.1 < x < 0.18 in the same system. Although several of these discrepancies have been widely attributed to the microstructure features arising from different synthesis processes, a detailed, systematic study is required, in order to properly understand the nature, compositions and characteristics of these phase transitions.…”

“…Crystal structures, phase transitions and physical properties of NBT, in bulk ceramic forms, have been widely investigated since its discovery by Smolensky in 1960 [1]. The intriguing phase transitions of both NBT and NBT-based solid solutions as a function of composition and temperature make them an excellent model for studies on the phase transition behaviors of relaxor ferroelectrics [2][3][4][5]. (Na 1/2 Bi 1/2 ) 1−x Pb x TiO 3 [NBPT (x)] is one of such solid solutions that have been reported in the literature.…”

Raman spectroscopy study of the Na0.5Bi0.5TiO3–PbTiO3 system

“…The room temperature tetragonality c/a changes from 1.06 for PT to 1.02 for the maximum of NBT solubility (NBT82-PT18), the decrease being more pronounced when the NBT content becomes larger than 30 mol% as shown in Fig. 4 [14]. Such a behaviour appears in the observed evolution of the Raman spectra with the composition.…”

“…5. Taking into account that (i) the tetragonal symmetry exhibited by the solid solutions decreases as the NBT content increases and (ii) the band at 280 cm À 1 is dominated by the Ti -O vibrations, such a coalescence of the two bands was expected with respect to the XRD data [6][7][8]14]. As for the bands located in the 450 -700 cm À 1 , they broaden and are shifted upwards.…”