Institute of High Pressure Physics

Dear Colleagues,

We are pleased to invite you to the next IHPP PAS Seminar on Nitride Semiconductors. The talk will be held in a hybrid mode – at the seminar room in New Technologies building, Al. Prymasa Tysiąclecia 98, and through Zoom platform (to get the link, please contact us at nitride_seminar@mail.unipress.waw.pl ).

The talk is scheduled on Tuesday 13.05.2025 at 15:00 CEST.

Speaker: Dr. Tomasz Jakubczyk (Faculty of Physics, University of Warsaw, Poland)

Title: Spectroscopy of single-photon color centers in GaN

Abstract: Link

Sincerely,

Tadeusz Suski
Piotr Perlin
Anna Kafar

FeSe is the simplest iron-based superconductor and has a layered structure with alternating Fe and Se layers. Dr. Singh's research group from our Institute has studied the chemical pressure effect by substitution of the Pr element at Fe sites and As-substitution at Se-sites in FeSe compound. Conventional synthesis process (CSP) at ambient pressure and high-pressure growth technique were used. Interestingly, Pr doping at Fe sites preserves T_c^onset and improves J_c of FeSe_0.5Te_0.5 regardless of the doping contents and growth conditions. More detail about this study can be found in the recently published paper by: Priya Singh, Manasa Manasa, Mohammad Azam, Tatiana Zajarniuk, Svitlana Stelmakh, Taras Palasyuk, Jan Mizeracki, Tomasz Cetner, Andrzej Morawski, Cezariusz Jastrzębski, Michał Wierzbicki, Shiv J. Singh entitled “Praseodymium doping effect on the superconducting properties of FeSe_0.5Te_0.5 bulks under ambient and high-pressure growth conditions” Physica C: Superconductivity and its Applications (Elsevier) 633, 1354729 (2025); https://doi.org/10.1016/j.physc.2025.1354729

Figure: The variation of (a) the onset transition temperature (T_c) (b) the transition width (ΔT) (c) the room temperature resistivity (ρ_300K) (d) residual resistivity ratio (RRR = ρ_300K / ρ_20K) (e) the critical current density (J_c) at 7 K for H = 0 T (closed symbol) and 3 T (open symbol) for Pr_xFe_1-xSe_0.5Te_0.5 bulks prepared by high pressure growth method with respect to the nominal contents (x) of Pr substitutions or Gd- additions.

In the second research paper, Dr. Singh’s research group has concluded their findings on the effects of As-substitution at Se sites in the FeSe system. The observed superconducting transition temperature is approximately 12 K, which is higher than that of the parent compound FeSe_1-x. This paper is published by: Priya Singh, Manasa Manasa, Mohammad Azam, Tatiana Zajarniuk, Konrad Kwatek, Tomasz Cetner, Andrzej Morawski, Jan Mizeracki and Shiv J. Singh entitled “Synthesis and characterizations of arsenic doped FeSe bulks” Journal of Superconductivity and Novel Magnetism 38, 109 (2025) https://doi.org/10.1007/s10948-025-06952-5

Congratulations to Dr. Eng. Aleksander Szpakiewicz-Szatan on receiving his academic title. On March 21, 2025, he successfully defended his doctoral dissertation at the Faculty of Physics of the Warsaw University of Technology (WUT), titled: "Nanocomposites from pressure-formed sodium-phosphate and bismuth glasses for applications in energy storage and conversion devices." A summary of the dissertation is available at the provided link. More information here.

Supervisors: Prof. Jerzy Garbarczyk, (Faculty of Physics, Warsaw University of Technology) and Prof. Sylwester Rzoska (Institute of High Pressure Physics, Polish Academy of Sciences).

The conferment of the PhD degree was approved today (April 24, 2025), by the Scientific Discipline Council of the Faculty of Physics, WUT.

The dissertation was developed as part of an ongoing collaboration between the NL-10 Laboratory (X-Press Matter) at the Institute of High Pressure Physics, PAS, and the Solid State Ionics Division of the Faculty of Physics, WUT. This collaboration will continue under a joint research grant.

We are pleased to inform about the work on spontaneous and piezoelectric polarization published recently in Materials: P. Strak, P. Kempisty, K. Sakowski, J. Piechota, I. Grzegory, E. Monroy, A. Kaminska, S. Krukowski, Spontaneous and Piezo Polarization Versus Polar Surfaces: Fundamentals and Ab Initio Calculations, Materials 2025, 18(7), 1489; https://doi.org/10.3390/ma18071489

The study discusses the fundamental properties of spontaneous and piezoelectric polarization as well as surface polarization. It has been shown that Landau’s definition of polarization as dipole density can be applied to infinite systems. Two components of polarization were distinguished: bulk polarization and surface polarization. This division is consistent with numerous experimental data. A local model of spontaneous polarization was introduced and used to calculate spontaneous polarization in the form of electric dipole density. This model correctly predicted the values of spontaneous polarization for wurtzite-type nitride semiconductors. At the same time, the model showed zero polarization for the zinc blende lattice. The values of spontaneous polarization obtained for wurtzite group III nitrides were consistent with previous calculations carried out using the Berry phase method. First-principles calculations for wurtzite nitride superlattices using the Heyd–Scuseria–Ernzerhof approximation were performed to calculate polarization fields in regularly strained lattices, showing good agreement with the polarization results. These data were used to determine the piezoelectric parameters of wurtzite nitrides, yielding values consistent with earlier results.