Pierre-Eymeric Janolin

Giant room-temperature barocaloric effect and pressure-mediated electrocaloric effect in BaTiO3 single crystal

Barocaloric effect in BaTiO3 single crystal is studied by a thermodynamic phenomenological model. It is demonstrated that a giant barocaloric effect can be achieved near room temperature with an adiabatic temperature change of more than 3u2009K and a temperature span about 50u2009K. As expected, the electrocaloric peak can be shifted towards room temperature by pressure. However, a slight reduction of the electrocaloric peak is found in contrast to relaxor ferroelectrics and LiNbO3. We believe that our findings could open a potential route by combining the barocaloric effect and pressure-mediated electrocaloric effect in BaTiO3 single crystal for cooling devices.

Temperature evolution of the structural properties of monodomain ferroelectric thin film

The structural evolution of epitaxial monodomain (only 180° domains) ferroelectric PbTiO3 thin film has been investigated, using high-resolution, temperature-dependent, x-ray diffraction. The full set of lattice parameters was obtained from room temperature up to 850K. It allowed the calculation of the different strains stored in the film at room temperature, underlying the difference between the mechanical strain and the misfit strain. The evolution of the misfit strain as a function of temperature was also calculated and was found to be consistent with the theoretical temperature-misfit strain phase diagram. These data strongly suggest that the film remains ferroelectric and tetragonal up to 940K.

Partial decoupling between strain and polarization in mono-oriented Pb(Zr0.2Ti0.8)O3 thin film

The structural evolution of epitaxial mono-oriented (i.e., with the c axis perpendicular to the interface) ferroelectric Pb(Zr0.2Ti0.8)O3 thin film has been investigated, using high-resolution, temperature dependent, x-ray diffraction. The full set of lattice parameters was obtained; it allowed to estimate the variation of the polarization as a function of temperature, underlying the difference between the polarization-induced tetragonality and the elastic one. The temperature evolution of the misfit strain has been calculated and found to be in good agreement with the theoretical temperature-misfit strain phase diagram.

Uniaxial-stress induced phase transitions in [001]C-poled 0.955Pb(Zn1∕3Nb2∕3)O3–0.045PbTiO3

First order rhombohedral to orthorhombic stress-induced phase transitions have been evidenced by bulk charge-stress measurements and x-ray diffraction derived lattice strain measurements in [001]C-poled 0.955Pb(Zn1∕3Nb2∕3)O3–0.045PbTiO3 (PZN-4.5PT). The transitions are induced by uniaxial compressive loads applied either along or perpendicular to the poling direction. In each case, they occur via rotation of the polar vector in the Cm monoclinic plane and the induced lattice strain is hysteretic yet reversible. Although no depoling is observed in the transverse mode net depolarization is observed under longitudinal stress which is important for the use of [001]C-poled PZN-PT and (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 single crystals in Tonpilz-type underwater projectors.

Domain structure sequence in ferroelectric Pb(Zr0.2Ti0.8)O3 thin film on MgO

The structural evolution of a polydomain ferroelectric Pb(Zr0.2Ti0.8)O3 film was studied by temperature-dependent x-ray diffraction. Two critical temperatures were evidenced: T*=740K, corresponding to a change in the domain structure (a∕c∕a∕c to a1∕a2∕a1∕a2), and TCfilm=825K, where the film undergoes a ferroelectric-paraelectric phase transition. The film remains tetragonal on the whole range of temperature investigated. The evolutions of the domain structure and lattice parameters were found to be in very good agreement with the calculated domain stability map and theoretical temperature-misfit strain phase diagram, respectively.

Structural transition in LaVO3/SrVO3 superlattices and its influence on transport properties

Measurements of the resistive properties and the lattice parameters of a (LaVO3)[6 unit cells]/(SrVO3)[1 unit cell] superlattice between 10 K and room temperature are presented. A low temperature metallic phase compatible with a Fermi liquid behavior is evidenced. It disappears in the vicinity of a structural transition from a monoclinic to tetragonal phase, in which disorder seems to strongly influence the transport. Our results will enrich the understanding of the electronic properties of complex heterostructures.