Crossover from classical to relaxor ferroelectrics in BaTi_1−xHf_xO₃ceramics

Abstract

In this paper we report the successful preparation of hafnium substituted barium titanate, i.e. BaTi1−xHfxO3 (BHT) ceramics with (x = 0.05,0.1,0.2,0.3 and 0.4). X-ray diffraction measurements followed by Reitveld analysis show the single-phase nature of these ceramics undergoing a tetragonal to cubic phase transformation for x≥0.10. Temperature dependent dielectric properties (ε′ and ε′′) of these single-phase BHT ceramics have been studied in the temperature range 90–375 K and frequency range 0.1–100 kHz. Dispersionless but hysteric ε′–T and ε′′–T behaviour has been observed for x<0.3 whereas for x≥0.3 highly diffusive and depressive ε′–T and ε′′–T behaviour has been observed. The three different phase transitions of pure BaTiO3 get pinched into a single diffused round peak along with frequency dispersion for x≥0.3. This clearly indicates an evolution of classical to relaxor ferroelectrics crossover with increasing x in these BHT ceramics. The parameters characterizing the relaxor behaviour have been analysed. The mechanism for the dielectric relaxation process and pinching of phase transition and their effect on ferroelectric behaviour is discussed.

Pyroelectric energy harvesting using low–TC (1–x)(Ba0.7Ca0.3)TiO3–xBa(Zr0.2Ti0.8)O3 bulk ceramics

“…It can be seen from Figure that T C decreased by ~16°C from BCTZ20(T) to BCTZ50(O) and by ~41°C from BCTZ50(O) to BCTZ80(R), which implies a normal–to–relaxor ferroelectric crossover. Several studies have revealed that such a sharp decline should be observed in areas that demonstrate intermediate states between ferroelectric and relaxor behaviors . The diffuseness of the paraelectric to ferroelectric transition can be evaluated using the modified Curie‐Weiss law as follows: where γ and C are assumed to be constant and γ is between 1 and 2, and T εm is temperature where the maximum dielectric constant ε rm .…”

“…Note that the letter in parenthesis following the composition indicates the crystal structure. This is probably the pinching phase transition of the three phase transitions (C–T, T–O, and O–R), which is often observed when the Ti site of BaTiO 3 is substituted by ions such as Zr, Sr, Ce, and Hf . For Ba(Ti, Zr)O 3 , the three phase transitions (C–T, T–O, and O–R) began to overlap with increasing Zr content, and finally the strong increase and broadening of the dielectric anomaly was maximized at a Zr content of ~0.10.…”

“…Several studies have revealed that such a sharp decline should be observed in areas that demonstrate intermediate states between ferroelectric and relaxor behaviors. 26 The diffuseness of the paraelectric to ferroelectric transition can be evaluated using the modified Curie-Weiss law as follows:…”

Effect of oxygenation on the structural and dielectric properties of Sr1−xCaxTiO3 with 0.20⩽x⩽0.40

“…For the first set, we directly used the as crushed powders, but for the second one, the crushed powders were first annealed in high purity ͑99.99%͒ oxygen atmosphere at 950°C for 24 h. The two sets of the pelletized ceramics were then sintered at 1350°C for 12 h. The final sintered samples were subjected to x-ray diffraction ͑XRD͒, transmission electron microscopy ͑TEM͒, and temperature dependent dielectric characterizations. 11 Details of TEM and the dielectric measurement are given elsewhere. 8,11 All the pellets were found to be similarly dense, ϳ95% of their corresponding x-ray density.…”

“…11 Details of TEM and the dielectric measurement are given elsewhere. 8,11 All the pellets were found to be similarly dense, ϳ95% of their corresponding x-ray density. Figure 1͑a͒ shows the XRD data of oxygenated SCT ceramics, which were Rietveld refined using space groups a͒ Author to whom correspondence should be addressed.…”