Search results for "ferroelectric"
showing 10 items of 374 documents
PHASE TRANSITIONS IN THE PLZT x/85/15 SOLID SOLUTIONS
2008
ABSTRACT Role of a La on the nature of phase transition in the PLZT x/85/15 is compared with the PLZT compositions of lower Zr/Ti ratio. Thermal dependence of the dielectric permittivity, thermal expansion and elastic modulus reveal sequential transfer from macroscopic ferroelectric to antiferroelectric and nonpolar state, if La concentration is increased. Diffused, from frequency independent thermal dependence of dielectric permittivity for compositions in certain La concentration range above 4 at% coexist with the well expressed phase transition between paraelectric and antiferroelectric phases.
Broadband dielectric spectroscopy of PbMg1/3Nb2/3O3–PbSc1/2Nb1/2O3 ceramics
2010
Abstract Broadband dielectric spectroscopy results of various ordered and disordered (1 − x)Pb(Mg1/3Nb2/3)O3–(x)Pb(Sc1/2Nb1/2)O3 (PMN–PSN) ceramics are investigated in the temperature range from 80 K to 300 K and frequency range from 20 Hz to 2 THz. Dielectric dispersion is very broad and in the ferroelectrics case (x = 1, 0.95) consists of two parts: low-frequency part caused by ferroelectric domains and higher frequency part caused by soft mode. The relaxational soft mode exhibits pronounced softening close to phase transition temperature, as it is typical for order–disorder phase transitions. By substituting Sc3+ by Mg2+ in PMN–PSN ceramics relaxation slows down, and for relaxors (x = 0.…
Radiation effects in transparent ferroelectric ceramics
1997
Radiation of different types ((gamma) -rays, electrons, neutrons) and fluence has been used to study the defect processes as well as the change of physical parameters in PLZT X/65/35 (X equals 4.5 - 11 at.%) and PbSc 0.5 Nb 0.5 O 3 (PSN) ceramics and to evaluate critical irradiation conditions. Effects on optical (extinction) spectra and dielectric characteristics (polarization, thermal and frequency dependences of dielectric permittivity (epsilon) and losses), dependent on composition and state of phase and polarization have been analyzed by means of annealing in isochronic and prolonged time regimes. A gradual shift of extinction edge to longer wavelengths, reduction of polarization and (…
Size effects of static and dynamic polarization in ferroelectric thin film multilayers
2001
Abstract A thermodynamic theory for the calculation of static and dynamic polarization profiles of ferroelectric thin film multilayers is developed. The free energy functional is written down using a multilayer model in which c-domain layers of the ferroelectric material alternate with a-domain layers of a second ferroelectric materials. We assume that the interfaces are perfectly sharp and that the polarization at these boundaries is zero. The equilibrium polarization profile, its temperature and thickness dependencies were determined from the solutions of the Euler-Lagrange equations. A thickness induced ferroelectric phase transition is shown to exist and its transition temperature and c…
Broadband Dielectric Spectroscopy of Ferroelectric Phase Transitions in PbSc1/2Nb1/2O3Ordered Ceramics
2008
Broadband dielectric spectroscopy of PbSc 1/2 Nb 1/2 O 3 (PSN) ordered ceramics are reported within the range of 20 Hz ≤ ν ≤ 2 THz in 80 K ≤ T ≤ 300 K temperatures. Spectrally very broad dielectric dispersion consisting of two parts − at lower frequencies, ferroelectric domains cause a dispersion and at higher frequencies, higher temperatures the relaxation soft mode is responsible for the dispersion. The relaxation soft mode exhibit pronounced hardening on cooling, whilst the ferroelectric phase transition is connected with an abrupt freezing and rise of polar nanoregions into ferroelectric domains.
Physical properties of ferroelectric film with continuous space charge distribution
2014
We present a theory of ferroelectric phase transitions in a film with a homogeneously distributed space charge leading to the so-called built-in polarization. On the base of our complete solution of the problem of continuous space charge distribution in a ferroelectric film, we calculate the ferroelectric phase transition temperature , spatial polarization distribution in paraelectric and ferroelectric phases as well as hysteresis loop in the ferroelectric phase. We have shown that the presence of continuous space charge in a film inhibits the ferroelectricity in it: it lowers the ferroelectric phase transition temperature and coercive field. Our estimates of these differences show that the…
Microstructure, calorimetric and dielectric investigation of hafnium doped barium titanate ceramics
2013
Ferroelectric properties of BaTi1− x Hf x O3 ceramics with Hf content x = 0, 0.001, and 0.025 were examined. It was found that the substitution of Hf4+ for Ti4+ in BaTiO3 resulted in shifting the two low-temperature transitions (T 1, T 2) of the investigated samples to higher temperatures and decreasing the tetragonal-cubic phase transition temperature (T c). This is a well-known pinching effect. Thermal parameters of the transitions, such as the enthalpy ΔH and the entropy ΔS, were also estimated and discussed.
Dielectric nonlinearity of the PBB′B″O3 ferroelectric solid solutions
2001
Abstract Obtaining of novel thin film materials for electrically tuneable capacities is one of the current problems of ferroelectric material application. Suitable ferroelectric compounds exhibiting broad phase transitions and small dielectric loss in the paraelectric phase have been searched for the purpose. Lead-containing niobates PbMg1/3Nb2/3O3 (PMN), PbNi1/3Nb2/3O3 (PNN) and PbZn1/3Nb2/3O3 (PZN) and their solid solutions have been found as most appropriate. Materials have been synthesized by solid phase reactions from the relevant oxides; ceramic samples were obtained by conventional ceramic technology. Results of the studies of thermal dependence of dielectric permeability and loss fa…
Specifics of polarisation switching in PbNi1/3Nb2/3O3–PbTiO3–PbZrO3 ferroelectric ceramics
2004
Abstract The growing interest in disordered relaxor ferroelectrics is due to unusual properties mainly related to the existence of broad phase transitions characteristic to the systems. The effects of bias field on the dielectric response and polarisation switching are studied in the 0.5 PbNi 1/3 Nb 2/3 O 3 – x PbTiO 3 –(0.5− x ) PbZrO 3 system at different PbTiO 3 :PbZrO 3 ratio. Thermal behaviour of normalised remnant polarisation P r / P max of compositions with content of lead titanate x =0.33 and x =0.35 at frequency 0.1 Hz and different values of field E o are measured. Results of measured polarisation and depolarisation currents are compared with characteristics of polarisation switc…
Applications of Liquid Crystalline Elastomers
2012
This chapter focuses on recent developments in the field of liquid crystalline elastomers (LCEs) that bring these materials closer to the world of real applications, concentrating on their actuation properties. First, we briefly introduce different LCE materials that show actuation behavior and explain how they can be synthesized. In the second part, we focus on materials in which a shape change is triggered by a phase transition. In particular, we discuss how the chemistry of the polymeric material influences the strength and direction of the shape change. We review the efforts made to trigger the actuation event by stimuli other than temperature variation. Subsequently, we summarize prepa…