Elastic and electronic properties and stability of SrThO3, SrZrO3 and ThO2 from first principles

doi:10.1016/j.jnucmat.2006.11.003

Journal of Nuclear Materials

Volume 361, Issue 1, 31 March 2007, Pages 69-77

https://doi.org/10.1016/j.jnucmat.2006.11.003 Get rights and content

Abstract

First-principle calculations in the framework of the full-potential linearized-augmented-plane-wave method (FLAPW, as implemented into the WIEN-2k code) have been performed to understand the structural, elastic, cohesive and electronic properties of the meta-stable cubic strontium thorate SrThO₃. The optimized lattice parameters, elastic parameters, formation energies, densities of states, band structures and charge density distributions are obtained and discussed in comparison with those of cubic SrZrO₃ and ThO₂.

Introduction

Thorium-based nuclear fuels are of great interest for the future nuclear industry. For example, it is proposed to use a ThO₂ matrix with admixtures of uranium and plutonium oxides as advanced fuel materials for the thermal breeder reactors and high-temperature gas cooled reactors. In this context, the presence of low-density phases such as ternary oxides M₂ThO₃ or MThO₃ forming due to the interaction of the fission products (M = Rb, Ba, Sr, etc.) with thoria, may critically affect the properties of the fuel such as thermal expansion, conductivity, and can be also responsible for the swelling of the fuel pins, see [1], [2], [3].

Since strontium is among the predominant fission products, the properties of the perovskite-like strontium thorate (SrThO₃) caused a lot of interest during the last decade [1], [2], [3], [4], [5]. Furthermore, the perovskite-type multi-component oxides of actinides are interesting candidates for hydrogen sensors, hydrogen gas separators, and are useful materials for many other electrochemical applications because of the unusual combination of their electronic and transport properties [6].

For the first time the synthesis of SrThO₃ by a conventional solid state route was reported in 1947 by Mary-Szabo [7]. More recently, Subasri et al. [5] noted the very limited solubility of SrO in thoria, and the formation of the single ternary phase is not achieved. On other hand, SrThO₃ samples are successfully prepared by a sol–gel method through the gel combustion technique [2], [3], [4].

The stability of SrThO₃ phase was discussed [3], [4], using experimentally derived and calculated thermodynamic properties. The values of the Gibbs energy formation of SrThO₃ reveal that this compound is meta-stable in comparison with its constituent oxides (SrO and thoria), and as a consequence, there are difficulties to synthesize single phase strontium thorate. Among the other SrThO₃ properties, up to now only the structural data [1], [2], [8] and the linear thermal expansion coefficients [1] are reported. A qualitative explanation of the relative stability of perovskites SrMO₃ (in particular, for M⁴⁺ ions) has been made [4] in terms of Goldschmidt’s tolerance factor t [9], which represents the size effect by means of the packing of spherical ions. It is based on ionic radii i.e. purely ionic bonding is assumed. For the stable SrMO₃ phases, the t-factor lies between 1.0 and 0.8 (for example, for SrZrO₃ t = 0.861), whereas for SrThO₃ the tolerance factor is about 0.780, i.e. this compound is placed on the border of the area of structural stability of perovskites, see for example reviews [10], [11].

However, today any data concerning the electronic and cohesion properties and chemical bonding in SrThO₃ are absent, and the available attempts to explain the stability of this compound at the atomistic level are based on oversimplified models [4]. It is well known, that the first-principle calculations based on the density-functional theory (DFT) are an effective tool for the understanding and predicting of the various properties of the family of perovskites at the electronic level.

In this work to get better insight in the nature of this material the first-principle density-functional theory calculations using the full-potential linearized-augmented-plane-wave (FLAPW) method have been performed. Here we concentrate on the peculiarities of the elastic, cohesive and electronic properties of SrThO₃ (in assumption of cubic phase) – in comparison with thoria and the isoelectronic Sr zirconate SrZrO₃ (Zr⁴⁺). Note that SrZrO₃ is also suitable for use in high-temperature applications such as fuel cells, steam electrolysis, and hydrogen gas sensors [12], [13], [14].

For SrThO₃, in result, the elastic constants (C_ij) are predicted and analyzed in comparison with those for ThO₂ and SrZrO₂. We employed the Voigt–Reuss–Hill (VRH) method to evaluate elastic parameters for these polycrystalline materials from C_ij of single crystals. In this way for the first time, the main elastic parameters for polycrystalline SrThO₃, ThO₂ and SrZrO₂: bulk modulus (B₀), compressibility (β), shear modulus (G), Young modulus (Y), Poisson ratio (ν), Lame constants (λ, μ) are predicted and analyzed. Next, using total energy calculations, the heats of formation of the mentioned Th, Zr-based perovskites (in assumption of formal reactions: SrThO₃ ↔ SrO + ThO₂ and SrZrO₃ ↔ SrO + ZrO₂) were estimated and discussed. The electronic bands and densities of states for ThO₂, SrThO₂ and SrZrO₂ have been obtained by study of their electronic properties. Finally, we assess the oxygen Kα X-ray emission spectra (XES; O: 2p ↔ s transitions) for ThO₂ and SrThO₃ – for discussion of the applicability of this method for the characterizations of these systems.

Section snippets

Models and method

Perovskite SrThO₃ is reported in JCPDS data [8] to have a pseudo-monoclinic unit cell with a = b = c = 0.884 nm and β = 90°, whereas according to Purohit et al. [1] SrThO₃ was monoclinic with lattice parameters a = 0.6319; b = 0.3240; c = 0.4928 nm and β = 117.38°.

On the first stage, the considered SrMO₃ perovskites (here M = Th and Zr) are assumed to have ideal cubic structure (s.g. 2 2 1) where atomic positions in the elementary cell are M: 1a (0, 0 0); I: 3d (0, 0, 1/2,); and Sr: 1b (1/2, 1/2, 1/2). Thoria adopts also

Elastic properties

The calculated equilibrium lattice constants (a₀) for cubic SrThO₃, SrZrO₃ as well as for ThO₂ are given in Table 1, and are in a reasonable accordance with the available data. For SrThO₃ the predicted a₀ is higher than a₀ (SrZrO₃) by ∼9.2 %. This result can be easily explained by considering the radii of cations: R(Zr⁴⁺) = 0.072 nm versus R(Th⁴⁺) = 0.092 nm.

Next, we have obtained the elastic constants (C_ij) for cubic SrThO₃, SrZrO₃ and ThO₂. These three independent elastic constants in a cubic

Conclusions

In this work, the ab initio FLAPW-GGA method has been used for study of structural, elastic, cohesive and electronic properties of the meta-stable strontium thorate SrThO₃ in comparison with ThO₂ and SrZrO₃.

We have predicted the elastic constants for SrThO₃ and have discussed them in comparison with ThO₂ and SrZrO₃. We have utilized the Voigt–Reuss–Hill approximation to estimate the main elastic parameters (bulk modulus, compressibility, shear modulus, Young modulus, Poisson ratio, Lame

Acknowledgement

This work was supported by the Russian Foundation for Basic Research, Grant No. 06-08-00808.

References (54)

R.D. Purohit et al.
J. Nucl. Mater.
(2000)
S. Dash et al.
J. Alloys Compd.
(2005)
R. Prasad et al.
J. Nucl. Mater.
(2003)
R. Subasri et al.
J. Nucl. Mater.
(2003)
S.F. Matar
Progr. Solid State Chem.
(2003)
T. Yajima et al.
Solid State Ionics
(1995)
U. Benedict
J. Less Common Met.
(1987)
R. Terki et al.
Comput. Mater. Sci.
(2005)
S. Yamanaka et al.
J. Nucl. Mater.
(2005)
W.P. Ellis et al.
Solid State Commun.
(1989)

J. Robertson et al.

Thin Solid Films

(2006)

S. Tang et al.

Appl. Surf. Sci.

(1998)

M. Ali (Basu) et al.

J. Nucl. Mater.

(2003)

H. Iwahara

I. Mary-Szabo, Publ. Univ. Tech. Sci. Budapest, 1, 1947,...

PC-PDF data, JCPDS-ICDD, 4-592,...

L.R. Goodenough et al.

(1970)

I. Solovyev et al.

Phys. Rev. B

(1996)

H. Iwahara et al.

J. Electrochem. Soc.

(1993)

N. Kurita et al.

J. Jpn. Inst. Met.

(1994)

P. Blaha et al.

J.P. Perdew et al.

Phys. Rev. Lett.

(1996)

P.E. Blöchl et al.

Phys. Rev. B

(1994)

A. Neckel et al.

Microchim. Acta

(1975)

B.J. Kennedy et al.

Phys. Rev. B

(1999)

A.J. Smith et al.

Acta Crystallogr.

(1960)

R. Terki et al.

Phys. Status Solidi B

(2005)

Cited by (53)

DFT based computational investigations of the physical properties of perovskites-structure SrXO<inf>3</inf> (X = Si, Tb, Th) for optoelectronic and thermo-mechanical applications
2024, Materials Today Communications
Density Functional Theory (DFT) method is employed for investigating the structural, elastic, electronic, optical, and thermal properties of Perovskite structure SrXO₃ (X = Si, Tb, and Th). The studied lattice parameters show good agreement with the previous theoretical and experimental results. The elastic stiffness constants, ${(C}_{ij})$ of SrSiO₃, SrTbO₃, and SrThO₃ satisfied the born stability criteria which confirm the mechanical stability of these phases. It is observed that when Tb or Th is replaced with Si, the brittleness behaviours of SrTbO₃ or SrThO₃ change to ductility, which improves its machinability for industrial applications. The investigation of anisotropic factors of SrSiO₃, SrTbO₃, and SrThO₃ ensured that SrSiO₃ is more anisotropic than SrTbO₃ and SrThO₃. By evaluating the electronic properties, it can be advantageous for applying the topological insulators (TI), solar cells, or PV (Photovoltaic) cell fabrication. Furthermore, the optical properties are studied and detail discussed with SrXO₃ (X = Si, Tb, and Th). The reason of low Debye temperature (Θ_D) and low minimum thermal conductivity (K_min) has been perfectly explicated through the consideration of the mean atomic weight (M/n) of the compounds. Temperature-dependent of heat capacities (C_v, C_p) and linear thermal expansion coefficient (α) are also estimated using the quasi-harmonic Debye model and discussed. The SrTbO₃ and SrThO₃ compounds can be employed as potential thermal barrier coating (TBC) materials for high-temperature applications, according to the low values of K_min, Θ_D and α.
Epitaxial light actinide oxide thin films
2024, Thin Solid Films
Epitaxial thin films of ThO $_{2}$ and (U $_{x}$ Th $_{1 - x}$ )O $_{2}$ mixed oxides (MOX) have been synthesised by DC magnetron sputtering. The samples were characterised using x-ray diffraction and spectroscopic ellipsometry. Three epitaxial ThO $_{2}$ samples of different crystallographic orientations have been synthesised and confirmed by x-ray diffraction analysis. The samples are [1 1 1], [1 1 0] and [0 0 1] oriented, with lattice parameters determined to be 5.714 $\pm$ 0.001 Å, 5.707 $\pm$ 0.001 Å and 5.624 $\pm$ 0.001 Å respectively. Four [0 0 1] oriented epitaxial (U $_{x}$ Th $_{1 - x}$ )O $_{2}$ samples have been fabricated, across $0 \leq x \leq 1$ , with all samples found to have a unique specular direction. The mixed oxides were found to obey Vegard’s law, with lattice parameter varying linearly with ThO $_{2}$ content. Values for the optical band gap and optical constants of the epitaxial ThO $_{2}$ and MOX samples have also been determined by spectroscopic ellipsometry. The band gap determined for the three ThO $_{2}$ samples were in the 3.9 - 4.6 eV range, which is a slight underestimate compared to other experimental values. The optical band gap was found to vary approximately linearly with ThO $_{2}$ content, across the sample series. These films can be implemented in the research of thorium-based nuclear fuels, mixed actinide oxide nuclear fuel and the long term storage of nuclear waste forms.
Ab-initio investigation of crystal structure and pressure induced phase transition in ThO<inf>2</inf> and PuO<inf>2</inf>
2021, Materials Today Communications
We have investigated the crystal structure, phase transition and electronic properties of ThO₂ and PuO₂ using density functional theory (DFT). The lattice parameters of cubic ThO₂ and PuO₂ are found to be 5.62 Å and 5.48 Å, respectively. At higher pressure, AnO₂ (An = Th, Pu) shows a transition from fluorite (cubic) to cotunnite (orthorhombic) structure at 26.6 GPa with 6.08% collapse in volume for ThO₂ and 43.5 GPa with 7.22% collapse in volume for PuO₂. Cubic ThO₂ and PuO₂ show indirect band-gap of 4.32 eV and 2.46 eV respectively. Orthorhombic ThO₂ shows a direct band-gap of 3.57 eV while cotunnite PuO₂ also has an indirect band-gap of 1.21 eV. The band-gap decreases in cotunnite structure as compared to the cubic structure for both oxides. With an increase in pressure, the band-gap and covalent characteristic increase in cubic AnO₂.
An anti-counterfeiting strategy based on thermochromic pigment activated by highly Yb<sup>3+</sup> doped photothermal particles
2021, Journal of Alloys and Compounds
Citation Excerpt :
First, the partially fused particles of PTSrZr1 are smaller than those of the PTZr sample, which could be due to the low melting point of SrCO3 in comparison of ZrO2. And secondly, that the hardness of the c-ZrO2 phase is greater than that of c-SrZrO3 phase [32,33], which are the main crystalline phases in PTZr and PTSrZr1. For a better distribution of particles in an ink solution, the PTSrZr1 sample turns out to be a better option due to its smaller size, which is of big importance for a printing application.
The counterfeiting of products is one of the main crimes combated by private companies and governments worldwide. Therefore, numerous anti-counterfeiting mechanisms must be designed, and the photothermal properties of rare-earth doped materials provide the opportunity to formulate increasingly complex strategies. This work presents a series of highly Yb³⁺ doped Sr/Zr hybrid oxide particles with distinctive photo-responsive features that allow the design of an innovative anti-counterfeiting system in combination with a thermochromic pigment implemented by screen printing technique. Upon exposure of the samples to 975 nm laser diode (LD) irradiation, a fast increase of the temperature was observed, reaching temperatures from 82 to 215 °C according to the excitation power, and thus revealing the encrypted code during some seconds in a reversible way. This unique photothermal response was attributed mainly to the high amount of doping, and the inherent low thermal conductivity of the developed matrices. The reliability of the proposed system was systematically tested under different excitation wavelengths and powers, and upon exposition to an extrinsic source of heat. Such evaluation demonstrated the high-security level of the system, whose decoding can be performed only with specific light in a narrow region of the near-infrared (NIR) spectrum, additionally avoiding the use of more sophisticated equipment. The great advantages, both in manufacturing and decoding, allow our system to be implemented in anti-counterfeiting printing methods. In addition, we propose two models, the first to describe the origin of the high-temperature increase in our samples and the second to describe the dynamic temperature behavior.
Materials genome project: The application of principal component analysis to the formability of perovskites and inverse perovskites
2020, Computational Condensed Matter
We present a throughout multivariate technique in order to predict the formability of perovskites and inverse perovskites compounds, on the basis of the unified atomic-ionic radii of the different species. In this study we demonstrate the utility of the principal component analysis (PCA) and the partial least square methods (PLS) to examine the statistical impact of the perovskites and inverse perovskites intrinsic characteristics on their stability.
Consequences of lead incorporation in fluorite structured thoria
2019, Ceramics International
The outcome of incorporation of lead in fluorite structured thoria in terms of structure and electrical properties have been discussed. Samples with stoichiometries Th_1-xPb_xO_2-δ (x = 0.00 to 0.70) have been synthesized by a solution combustion route and characterized extensively. The maximum solubility limit of lead in fluorite structured thoria was deduced to be 50 mol % from powder X-ray diffraction and Raman spectral measurements. The micro strain of the fluorite lattice increased with the introduction of lead. X-ray photoelectron spectroscopy analysis of Th_0·50Pb_0·50O_2-δ showed the existence of lead in both +2 and + 4 oxidation states. The ratio between the intensities of peaks located at 548 cm⁻¹ and T_2g mode (I₅₄₈/I_T2g) was found to increase with increase in lead content in the samples and quantified utilizing grain size and half width half maxima. The defect concentrations in these samples have been estimated in the range 10¹⁷-10²⁰ cm⁻³. The direct band gap values shifted from the insulating regime (for thoria) to semiconducting regime (3.4–2 eV) for lead substituted samples. From the frequency dependent conductivity plots of Th_1-xPb_xO_2-δ samples over temperature range (323–773 K), highest conductivity of 1.62 × 10⁻⁶ Scm⁻¹ was obtained for Th_0·50Pb_0·50O_2-δ at 773 K. From the impedance measurements of lead substituted thoria under flowing oxygen (1 atm), thermal motion of oxygen ion vacancies was found responsible for the observed conductivity.

View all citing articles on Scopus

View full text

Elastic and electronic properties and stability of SrThO3, SrZrO3 and ThO2 from first principles

Abstract

Introduction

Section snippets

Models and method

Elastic properties

Conclusions

Acknowledgement

J. Nucl. Mater.

J. Alloys Compd.

J. Nucl. Mater.

J. Nucl. Mater.

Progr. Solid State Chem.

Solid State Ionics

J. Less Common Met.

Comput. Mater. Sci.

J. Nucl. Mater.

Solid State Commun.

Thin Solid Films

Appl. Surf. Sci.

J. Nucl. Mater.

Phys. Rev. B

J. Electrochem. Soc.

J. Jpn. Inst. Met.

Phys. Rev. Lett.

Phys. Rev. B

Microchim. Acta

Phys. Rev. B

Acta Crystallogr.

Phys. Status Solidi B

Elastic and electronic properties and stability of SrThO₃, SrZrO₃ and ThO₂ from first principles