Ex) Article Title, Author, Keywords
Ex) Article Title, Author, Keywords
New Phys.: Sae Mulli 2023; 73: 1183-1188
Published online December 31, 2023 https://doi.org/10.3938/NPSM.73.1183
Copyright © New Physics: Sae Mulli.
A. Henriques1, D. M. N. Oliveira1, M. Baksi2, M. Naveed1, W. H. Brito3, J. Larrea-Jimenez1, D. Kumah2, S. Wirth4, V. Martelli1*
1Laboratory for Quantum Matter under Extreme Conditions, Institute of Physics, University of São Paulo, São Paulo 05508-090, Brazil
2Department of Physics, North Carolina State University, North Carolina 27607, USA
3Department of Physics, Federal University of Minas Gerais, Belo Horizonte 31270-901, Brazil
4Max-Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
Correspondence to:*valentina.martelli@usp.br
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
The perovskite BaBiO3 crystallizes in a cubic structure and undergoes structural transitions toward lower symmetry phases upon cooling. The two low-temperature monoclinic phases are insulating, and the origin of this unexpected non-metallic character has been under debate. Both monoclinic phases exhibit tilting and breathing distortions, which are connected with their insulating nature and may have important effects on phononic heat conductivity. Here, we report the first thermal conductivity measurement, κ(T), in pristine polycrystalline BaBiO3 from 1.5 K to 310 K. At low and intermediate temperatures, we observe features reminiscent of a glass-like behavior, whereas at high-temperatures we find a downturn - typical of a crystalline solid. We compare our findings with available data of other recently investigated perovskite oxides displaying similar temperature dependence.
Keywords: Condensed Matter Physics, Thermal conductivity, Perovskites, BaBiO3, Glass-like systems
Barium bismuthate BaBiO3 (BBO) has attracted considerable attention due to its intriguing phase diagram and electronic properties[1, 2]. BBO exhibits an insulating ground state, whereas a metallic character is expected in a simple ionic picture considering a semi-filled Bi-6s shell[3]. Its cubic phase becomes superconducting upon hole-doping when either the Ba-site is replaced by Pb[4, 5] or the Bi-site is substituted by K[6], while the mechanism at the base of the superconducting state is still an open question. More recently, a theoretical prediction of a Topological Insulating state (TI) in electron-doped BBO re-ignited the interest in this compound[7, 8]. Over the last two decades, the feasibility of such a TI phase has been a matter of intense debate: theoretical calculations[8, 9] indicated that the massive amount of electrons required to elevate its Fermi energy by 2 eV in the cubic phase leads to structural instabilities, preventing the achievement of the predicted TI phase. Reduction of the sample thickness was then used as a tuning parameter to suppress tilting and breathing distortions[10-12], in the attempt to stabilize the cubic phase. Nevertheless, no metallicity was observed, leaving the persistent insulating state in BBO an open mystery.
Two possible mechanisms are currently proposed to be at the origin of the insulating state of BBO: an electrical charge disproportionation (CD) of Bi3+ and Bi5+ ions and a bond disproportionation associated with the hybridization of Bi-6s and O-2p orbitals with a unique bismuth valence[3]. Both come along with breathing and tilting distortions of the Oxygen-octahedra (Fig. 1(a)), causing a periodic distortion of the lattice. Recently, the gap formation was interpreted within a fractional CD, where the fluctuations are driven by the dynamical breathing modes of the octahedra[13]. Recent DFT+U+V calculations highlighted the importance of considering both on-site and intersite electronic interactions for the accurate description of the breathing distortions[14], suggesting a complex interplay between the electronic and lattice degrees of freedom.
Bulk BBO crystallizes in a cubic structure above 800 K and undergoes several structural transitions toward lower symmetry as a function of temperature. The crystalline BBO presents a rhombohedral structure (space group R
In this work, we present and discuss the temperature-dependent thermal conductivity
A two-step solid-state reaction was employed to synthesize crystals of BaBiO3: a 2:1 molar ratio of powders of BaCO3 and Bi2O3 was mixed and ground, and the mixture was annealed in an alumina crucible at 800 °C for 20 hours in flowing oxygen. The resulting BBO powder was re-ground for the recrystallization step as reported by Balendeh et al., who obtained single crystals of a few millimeters[16].
The apparent density of our crystals estimated from the weight and volume is
XRD data of powder BBO were acquired with a Rigaku Ultima III Diffractometer under
XRD patterns were analyzed by using the GSAS-II software[18] as shown in Fig. 1(b). Inside the experimental resolution, Rietveld refinement shows one single phase with space group I2/m for the monoclinic II phase. The lattice parameters were found to be a=6.1864 Å, b = 6.1403 Å, c=8.6736 Å and
Table 1 . Lattice parameters of the monoclinic II phase of BaBiO3 at ambient temperature obtained from Rietveld Refinement and comparison to literature.
Reference | a (Å) | b (Å) | c (Å) | β (°) | Phase |
---|---|---|---|---|---|
Kennedy (2006)[15] | 6.18505 | 6.13219 | 8.6585 | 90.229 | I2/m |
Chaillout (1985)[19] | 6.1721 | 6.1301 | 8.6617 | 90.048 | I2/m |
Zhou (2004)[20] | 6.19125 | 6.15264 | 8.69177 | 90.1115 | I2/m |
Yamaguchi (2005)[21] | 6.188 | 6.141 | 8.675 | 90.16 | I2/m |
Pei (1989)[22] | 6.1863(1) | 6.1406(1) | 8.6723(1) | 90.164(2) | I2/m |
Foyevtsov (2019)[23] | 6.1903(27) | 6.1471(27) | 8.6819(33) | 90.0764(47) | I2/m |
This work | 6.1864 | 6.1403 | 8.6736 | 90.06 | I2/m |
Based on the (x-ray) illuminated area, the crystallite sizes were estimated to be in the order of 0.75 mm2. In this work, as the transport properties are investigated in samples with a length of the order of 5 mm, the specimens are polycrystals with domain sizes of the order of the crystallites.
Analysis of electrical resistivity using the Arrhenius equation
Figure 3(a) shows
At low temperatures (T<6 K),
At intermediate temperatures (at a fraction of the Debye temperature
At high temperatures (T>200 K),
The behavior of
We end our discussion by comparing - see Table 2 - a few relevant values related to the thermal properties of BBO and another complex oxide, SrTiO3. At room-temperature, the magnitude of thermal conductivity is ten times less in BaBiO3 while vL (longitudinal sound velocity),
Table 2 . Thermal conductivity at room temperature
Compound | vL [km/s] | TM [K] | ||
---|---|---|---|---|
SrTiO3 | 10.8 | 7.87 | 397 | 2213 |
BaBiO3 | 1.20 | 4.40 | 229 | 1313 |
BaBiO3 polycrystals were obtained in a similar quality with respect to what was reported in the literature. The order of magnitude of barium bismuthate thermal conductivity was confirmed to be about 1 W m-1 K-1. Temperature-dependent measurements show features in
VM, AH, DMNO, MN acknowledge the support of São Paulo Research Foundation (FAPESP) grant number 2018/19420-3, 2022/01742-0, 2021/00625-7, 2022/03262-5 respectively. VM and DK acknowledge the University Global Partnership Network (UGPN) Research Collaboration Fund (RCF). JLJ acknowledges support of FAPESP (2018/08845-3) and CNPq-PQ2 (310065/2021-6). WHB acknowledges CNPq (402919/2021-1). We thank A. C. Franco of the Multi-user Laboratory of Crystallography at IF-USP for support during the XRD measurements.