arXiv subjects

W. Jo

Publications and source records attributed to W. Jo.

3 recordsLinked to original sources

arXiv2025

Quantitative correlation between structural (dis-)order and diffuseness of phase transition in lead scandium tantalate

Ferroelectrics show a phase transition to a paraelectric phase at a well-defined transition temperature. Introducing disorder makes this transition diffuse, and the system becomes a relaxor. Since the degree of (dis-)order is usually manipulated by varying the chemical composition, it is difficult to establish a direct relationship between disorder and the degree of diffuseness. Perovskite structured lead scandium tantalate (Pb[Sc$_{1/2}$Ta$_{1/2}$]O$_3$, PST) offers the opportunity to tune the character of the transition by thermal annealing without changing the stoichiometry. Here it is demonstrated that there is a linear correlation between the structural ordering, quantified by the intensity ratio $S$ of the pseudocubic (111)/(200) x-ray diffraction peaks, and the diffuseness parameter $\gamma$ deduced from temperature-dependent dielectric spectroscopy. The relation is universal, independent of whether the sample is a thin film, multilayer capacitor or bulk ceramic, and also independent of the absolute value of the dielectric permittivity.

cond-mat.mtrl-sci↗

arXiv2010

Control of defect-mediated tunneling barrier heights in ultrathin MgO films

The impact of oxygen vacancies on local tunneling properties across rf-sputtered MgO thin films was investigated by optical absorption spectroscopy and conducting atomic force microscopy. Adding O$_2$ to the Ar plasma during MgO growth alters the oxygen defect populations, leading to improved local tunneling characteristics such as a lower density of current hotspots and a lower tunnel current amplitude. We discuss a defect-based potential landscape across ultrathin MgO barriers.

cond-mat.mtrl-sci↗

arXiv2004

PES and XAS Study on Electronic Structures of Multiferroic RMnO$_3$ (R=Y, Er)

Electronic structures of multiferroic RMnO$_3$ (R=Y, Er) have been investigated by employing photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). We have found that Mn ions in RMnO$_3$ are in the trivalent high-spin state with the total spin of S=2. The occupied Mn ($d_{xz} - d_{yz}$) states lie deep below $\rm E_F$, while the occupied Mn ($d_{xy} - d_{x^2 -y^2}$) states overlap very much with the O $2p$ states. It is observed that the PES spectral intensity of Mn 3d states is negligible above the occupied O $2p$ bands, suggesting that YMnO$_3$ is likely to be a charge-transfer insulator. The Mn $d_{3z^2 -r^2}$ state is mostly unoccupied in the ferroelectric phase of YMnO$_3$.

cond-mat.mtrl-sci↗