Astri Bjørnetun Haugen

Structure and phase transitions in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) from −100 °C to 150 °C

The solid solution of (x)Ba0.7Ca0.3TiO3-(1-x)BaZr0.2Ti0.8O3 is known to exhibit high piezoelectric constants. Discrepancies in the reported phase transitions and structure around room temperature, however, have complicated the understanding of the enhanced properties. Rietveld refinement of high-resolution X-ray diffraction is employed here to establish and refine the crystallographic structure at temperatures from −100u2009°C to 150u2009°C for xu2009=u20090.5. A combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20u2009°C and −25u2009°C, bordered by single phase rhombohedral and tetragonal regions at lower (i.e., −100u2009°C) and higher (i.e., 70u2009°C) temperatures, respectively. The diffractograms also show signs of strain and domain wall scattering that are linked to the sample history.

Long-range symmetry breaking in embedded ferroelectrics

The characteristic functionality of ferroelectric materials is due to the symmetry of their crystalline structure. As such, ferroelectrics lend themselves to design approaches that manipulate this structural symmetry by introducing extrinsic strain. Using in situ dark-field X-ray microscopy to map lattice distortions around deeply embedded domain walls and grain boundaries in BaTiO3, we reveal that symmetry-breaking strain fields extend up to several micrometres from domain walls. As this exceeds the average domain width, no part of the material is elastically relaxed, and symmetry is universally broken. Such extrinsic strains are pivotal in defining the local properties and self-organization of embedded domain walls, and must be accounted for by emerging computational approaches to material design.Ferroelectricity can be modified by domain wall strain fields that extend over nanometres. Here, with X-ray microscopy, strain fields over several micrometres are observed in BaTiO3, suggesting ferroelectricity is globally altered throughout the material.

Structure and phase transitions in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) from -100 degrees C to 150 degrees C

The solid solution of (x)Ba0.7Ca0.3TiO3-(1-x)BaZr0.2Ti0.8O3 is known to exhibit high piezoelectric constants. Discrepancies in the reported phase transitions and structure around room temperature, however, have complicated the understanding of the enhanced properties. Rietveld refinement of high-resolution X-ray diffraction is employed here to establish and refine the crystallographic structure at temperatures from −100u2009°C to 150u2009°C for xu2009=u20090.5. A combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20u2009°C and −25u2009°C, bordered by single phase rhombohedral and tetragonal regions at lower (i.e., −100u2009°C) and higher (i.e., 70u2009°C) temperatures, respectively. The diffractograms also show signs of strain and domain wall scattering that are linked to the sample history.

Structure and phase transitions in 0.5(Ba[subscript 0.7]Ca[subscript 0.3]TiO[subscript 3])-0.5(BaZr[subscript 0.2]Ti[subscript 0.8]O[subscript 3]) from ;#8722;100;#8201;°C to 150;#8201;°C

The solid solution of (x)Ba0.7Ca0.3TiO3-(1-x)BaZr0.2Ti0.8O3 is known to exhibit high piezoelectric constants. Discrepancies in the reported phase transitions and structure around room temperature, however, have complicated the understanding of the enhanced properties. Rietveld refinement of high-resolution X-ray diffraction is employed here to establish and refine the crystallographic structure at temperatures from −100u2009°C to 150u2009°C for xu2009=u20090.5. A combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20u2009°C and −25u2009°C, bordered by single phase rhombohedral and tetragonal regions at lower (i.e., −100u2009°C) and higher (i.e., 70u2009°C) temperatures, respectively. The diffractograms also show signs of strain and domain wall scattering that are linked to the sample history.