1
|
Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ]. CRYSTALS 2021. [DOI: 10.3390/cryst12010035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The compound 0.9[KNbO3]-0.1[(BaNi1/2Nb1/2O3−δ] (KBNNO), a robust eco-friendly (lead-free) ferroelectric perovskite, has diverse applications in electronic and photonic devices. In this work, we report the dielectric, ferroelectric, and structural phase transitions behavior in the KBNNO compound using dielectric, X-ray diffraction, and Raman studies at ambient and as a function of temperature. Analyses of X-ray diffraction (XRD) data at room temperature (rtp) revealed the orthorhombic phase (sp. Gr. Amm2) of the compound with a minor secondary NiO cubic phase (sp. Gr. Fm3m). A direct optical band gap Eg of 1.66 eV was estimated at rtp from the UV–Vis reflectance spectrum analysis. Observation of non-saturated electric polarization loops were attributed to leakage current effects pertaining to oxygen vacancies in the compound. Magnetization studies showed ferromagnetism at room temperature (300 K) in this material. XRD studies on KBNNO at elevated temperatures revealed orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions at 523 and 713 K, respectively. Temperature-dependent dielectric response, being leaky, did not reveal any phase transition. Electrical conductivity data as a function of temperature obeyed Jonscher power law and satisfied the correlated barrier-hopping model, indicating dominance of the hopping conduction mechanism. Temperature-dependent Raman spectroscopic studies over a wide range of temperature (82–673 K) inferred the rhombohedral-to-orthorhombic and orthorhombic-to-tetragonal phase transitions at ~260, and 533 K, respectively. Several Raman bands were found to disappear, while a few Raman modes such as at 225, 270, 289, and 831 cm−1 exhibited discontinuity across the phase transitions at ~260 and 533 K.
Collapse
|
2
|
From SrTiO3 to Cuprates and Back to SrTiO3: A Way Along Alex Müller’s Scientific Career. CONDENSED MATTER 2020. [DOI: 10.3390/condmat6010002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
K.A. Müller took a long route in science leaving many traces and imprints, which have been and are still today initiations for further research activities. We “walk” along this outstanding path but are certainly not able to provide a complete picture of it, since the way was not always straight, often marked by unintended detours, which had novel impact on the international research society.
Collapse
|
3
|
Unconventional Co-Existence of Insulating Nano-Regions and Conducting Filaments in Reduced SrTiO3: Mode Softening, Local Piezoelectricity, and Metallicity. CRYSTALS 2020. [DOI: 10.3390/cryst10060437] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Doped SrTiO3 becomes a metal at extremely low doping concentrations n and is even superconducting at n < 1020 cm−3, with the superconducting transition temperature adopting a dome-like shape with increasing carrier concentration. In this paper it is shown within the polarizability model and from first principles calculations that up to a well-defined carrier concentration nc transverse optic mode softening takes place together with polar nano-domain formation, which provides evidence of inhomogeneity and a two-component type behavior with metallicity coexisting with polarity. Beyond this region, a conventional metal is formed where superconductivity as well as mode softening is absent. For n ≤ nc the effective electron-phonon coupling follows the superconducting transition temperature. Effusion measurements, as well as macroscopic and nanoscopic conductivity measurements, indicate that the distribution of oxygen vacancies is local and inhomogeneous, from which it is concluded that metallicity stems from filaments which are embedded in a polar matrix as long as n ≤ nc.
Collapse
|
4
|
He X, Bansal D, Winn B, Chi S, Boatner L, Delaire O. Anharmonic Eigenvectors and Acoustic Phonon Disappearance in Quantum Paraelectric SrTiO_{3}. PHYSICAL REVIEW LETTERS 2020; 124:145901. [PMID: 32338961 DOI: 10.1103/physrevlett.124.145901] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 01/19/2020] [Accepted: 03/16/2020] [Indexed: 06/11/2023]
Abstract
Pronounced anomalies in the SrTiO_{3} dynamical structure factor, S(Q,E), including the disappearance of acoustic phonon branches at low temperatures, were uncovered with inelastic neutron scattering (INS) and simulations. The striking effect reflects anharmonic couplings between acoustic and optic phonons and the incipient ferroelectric instability near the quantum critical point. It is rationalized using a first-principles renormalized anharmonic phonon approach, pointing to nonlinear Ti-O hybridization causing unusual changes in real-space phonon eigenvectors, frequencies, group velocities, and scattering phase space. Our method is general and establishes how T dependences beyond the harmonic regime, assessed by INS mapping of large reciprocal-space volumes, provide real-space insights into anharmonic atomic dynamics near phase transitions.
Collapse
Affiliation(s)
- Xing He
- Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA
| | - Dipanshu Bansal
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
| | - Barry Winn
- Neutron Scattering Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Songxue Chi
- Neutron Scattering Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Lynn Boatner
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Olivier Delaire
- Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA
- Department of Physics, Duke University, Durham, North Carolina 27708, USA
- Department of Chemistry, Duke University, Durham, North Carolina 27708, USA
| |
Collapse
|
5
|
Temperature–Power Simultaneous Effect on Physical Properties of BaxSr1−x TiO3 Thin Films Deposited by RF–Magnetron Cosputtering for 0 ≤ x ≤1. COATINGS 2018. [DOI: 10.3390/coatings8100362] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The combined effect on the variation of the in-situ deposition temperature and the variation of the applied power on the deposition rate (DR), gap energy (Eg), and resistivity (ρ) in barium strontium titanate thin films, deposited into RF (radio frequency)–magnetron cosputtering equipment, are presented in this research. The simultaneous action of two magnetrons (BaTiO3 and SrTiO3) is explained using the first and second derivative of Boltzmann’s sigmoidal equation. This found that a deposition gradient is a very novel analysis. Using the color-code lines built through MATLAB® and analyzing the trend information, taking into account the influence of the calculated “x” parameter, by means of the Boltzmann’s sigmoidal equation fit, we propose a method to set up an RF–magnetron cosputtering system to predict the DR(x,T), Eg(x,T), and ρ(x,T) values of BaxSr1−xTiO3 solid solutions with 0 ≤ x ≤ 1 for amorphous and crystalline phases. This method can be a versatile tool to optimize the deposition process with, or without, in situ deposition temperature.
Collapse
|
6
|
Prasad BE, Kazin P, Komarek AC, Felser C, Jansen M. β-Ag3 RuO4, a Ruthenate(V) Featuring Spin Tetramers on a Two-Dimensional Trigonal Lattice. Angew Chem Int Ed Engl 2016; 55:4467-71. [PMID: 26945558 DOI: 10.1002/anie.201510576] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Indexed: 11/09/2022]
Abstract
Open-shell solids exhibit a plethora of intriguing physical phenomena that arise from a complex interplay of charge, spin, orbital, and spin-state degrees of freedom. Comprehending these phenomena is an indispensable prerequisite for developing improved functional materials. This type of understanding can be achieved, on the one hand, by experimental and theoretical investigations into known systems, or by synthesizing new solids displaying unprecedented structural and/or electronic features. β-Ag3 RuO4 may serve as such a model system because it possesses a remarkable anionic structure, consisting of tetrameric polyoxoanions (Ru4 O16 )(12-) , and is an embedded fragment of a 2D trigonal MO2 lattice. The notorious frustration of antiferromagnetic (AF) exchange couplings on such lattices is thus lifted, and instead strong AF occurs within the oligomeric anion, where only one exchange path remains frustrated among the relevant six. The strong magnetic anisotropy of the [Ru4 O16 ](12-) ion, and the effectively orbital nature of its net magnetic moment, implies that this anion may reveal the properties of a single-molecule magnet if well-diluted in a diamagnetic matrix.
Collapse
Affiliation(s)
- Beluvalli E Prasad
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187, Dresden, Germany
| | - Pavel Kazin
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187, Dresden, Germany.,Department of Chemistry, Moscow State University, 119991, Moscow, Russia
| | - Alexander C Komarek
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187, Dresden, Germany
| | - Claudia Felser
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187, Dresden, Germany
| | - Martin Jansen
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187, Dresden, Germany. .,Max-Planck-Institut für Festkörperforschung, 70569, Stuttgart, Germany.
| |
Collapse
|
7
|
Prasad BE, Kazin P, Komarek AC, Felser C, Jansen M. β-Ag3RuO4, a Ruthenate(V) Featuring Spin Tetramers on a Two-Dimensional Trigonal Lattice. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201510576] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Beluvalli E. Prasad
- Max-Planck-Institut für Chemische Physik fester Stoffe; 01187 Dresden Germany
| | - Pavel Kazin
- Max-Planck-Institut für Chemische Physik fester Stoffe; 01187 Dresden Germany
- Department of Chemistry; Moscow State University; 119991 Moscow Russia
| | | | - Claudia Felser
- Max-Planck-Institut für Chemische Physik fester Stoffe; 01187 Dresden Germany
| | - Martin Jansen
- Max-Planck-Institut für Chemische Physik fester Stoffe; 01187 Dresden Germany
- Max-Planck-Institut für Festkörperforschung; 70569 Stuttgart Germany
| |
Collapse
|
8
|
|
9
|
|