Structure and phase transition of Na0.5La0.5TiO3

Garg, Rajni; Senyshyn, Anatoliy; Boysen, H.; Ranjan, Rajeev

doi:10.1088/0953-8984/20/50/505215

Cited by 17 publications

(14 citation statements)

References 23 publications

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“…Structural characterisation of La0.5Na0.5TiO3 (LNTO) with synchrotron powder X-ray and neutron diffraction gave good agreement with the reported rhombohedral structure (Fig. S1, Table S2, ESI †), 31 most importantly highlighting that La 3+ and Na + are fully disordered on the A site. Despite this, the anisotropic displacement parameters do not indicate a strong local deviation away from the average structure with a root mean square displacement of 0.078(9) Å for the A site at 300 K, showing that Please do not adjust margins Please do not adjust margins LNTO is a crystalline solid with disordered A site cation distribution.…”

supporting

confidence: 72%

Phonon-glass electron-crystal behaviour by A site disorder in n-type thermoelectric oxides

Daniels

Саввин

Pitcher

et al. 2017

Energy Environ. Sci.

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a Phonon-glass electron-crystal (PGEC) behaviour is realised in La0.5Na0.5Ti1-xNbxO3 thermoelectric oxides. The vibrational disorder imposed by the presence of both La 3+ and Na + cations on the A site of the ABO3 perovskite oxide La0.5Na0.5TiO3 produces a phonon-glass with a thermal conductivity, κ, 80% lower than that of SrTiO3 at room temperature. Unlike other state-of-the-art thermoelectric oxides, where there is strong coupling of κ to the electronic power factor, the electronic transport of these materials can be optimised independently of the thermal transport through cation substitution at the octahedral B site. The low κ of the phonon-glass parent is retained across the La0.5Na0.5Ti1-xNbxO3 series without disrupting the electronic conductivity, affording PGEC behaviour in oxides.Thermoelectric generators offer enhanced energy efficiency across the industrial and automotive sectors through the conversion of waste heat into electricity. Materials performance is assessed by the dimensionless figure of merit ZT = (S 2 σ/κ)T, combining the thermal conductivity (κ), absolute temperature (T), the Seebeck coefficient (S) and electrical conductivity (σ), which together define the power factor (S 2 σ). One strategy to optimise ZT is the phononglass electron-crystal (PGEC) concept proposed by Slack, 1 which aims to decouple the quantities governed by the Boltzmann transport equation in an "electron-crystal", by maximising S and σ, from the quantity governed by phonon transport processes in a "phonon-glass" (PG) by minimising the lattice contribution to the thermal conductivity (κlatt); essentially, a crystal that transports charge like a semiconductor, whilst hindering the transport of heat by the lattice like a glass. 2 Heat transport in solids consists of lattice and electronic (κelec) contributions through κ = κlatt + κelec, and κlatt=1/3Cv·lph·νs (Equation 1), where Cv is the isochoric heat capacity, lph the average phonon mean free path (MFP), and vs the mean velocity of sound. Different heat-carrying mechanisms lead to a broad distribution of MFPs, ranging from the atomic scale (<1 nm) for point defect scattering, to the mesoscale (>100 nm) for grain boundary scattering. In a "phonon-crystal" (PC), heat is transported by phonons of well-defined wavelength. The phonon scattering rate (ph -1 ), which is inversely proportional to κlatt (Equation S1, ESI †), corresponds to the sum of the inverse relaxation times of several phonon-scattering mechanisms that contribute separately to κ and is described quantitatively by the modified Debye-Callaway model (Equation S3, ESI †). 3 This produces a T -1 temperature dependence of κ above the Debye temperature (D) where heat conduction is by Oxide materials are of current interest as high-temperature energy-harvesting thermoelectrics in the automotive and manufacturing sectors due to their low cost, low toxicity and high chemical robustness. The phonon-glass electron crystal (PGEC) concept which has been successfully used to optimise the thermoelectric figure of merit (Z...

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supporting

confidence: 72%

Phonon-glass electron-crystal behaviour by A site disorder in n-type thermoelectric oxides

Daniels

Саввин

Pitcher

et al. 2017

Energy Environ. Sci.

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“…Using a combination of synchrotron and neutron powder diffraction data, Garg et al showed that

R \bar{3} c

was a better description of the structure of Na 0.5 La 0.5 TiO 3 than I 4 /mcm . The octahedral tilting about the hexagonal [001] was quantified at about 8°.…”

Section: Introductionmentioning

confidence: 90%

“…Others later proposed an orthorhombic structure in space group Pnma . Most recently, several groups have used synchrotron‐ and neutron‐diffraction data to establish either tetragonal ( I 4 /mcm ) or trigonal (

R \bar{3} c

) structural models, with a phase transition to an orthorhombic form in the region 0 < x < 0.05. Knapp & Woodward suggested that the A‐site ordering observed in the analogous perovskite (Na 0.5 La 0.5 )(Mg 0.5 W 0.5 )O 3 would imply that Na 0.5 La 0.5 TiO 3 should also have A‐site cation ordering; however, they observed no such long‐range ordering.…”

Section: Introductionmentioning

confidence: 99%

Empirical Evidence for A‐Site Order in Perovskites

et al. 2016

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Models for composition–structure relationships are useful in both the lab and industry, yet few exist for perovskites-containing extrinsic defects or cation ordering. In this work, an empirical model is used to predict the existence of A-site cation ordering. Specifically, four compositions in the Na(1−3x)/2La(1+x)/2TiO3 system (x = 0.0, 0.0533, 0.1733 and 0.225) were synthesized using a conventional solid-state mixed-oxide method. The structure of the x=0 end-member (Na0.5La0.5TiO3) has been reported in various space groups, but always with a random distribution of Na+ and La3+ on the A site; however, empirical modeling suggests that it is not only ordered but also that a small volume increase accompanies the ordering process. While no evidence of long-range A-site ordering is observed in this composition via X-ray or neutron diffraction, electron-diffraction data indicate short-range ordering of Na+ and La3+ ions, with the degree of cation ordering decreasing (but the scale of ordered domains and degree of vacancy ordering generally increasing) with increasing x. First-principles calculations via density functional theory support both conclusions that short-range ordering in Na0.5La0.5TiO3 is stable and that it results in a volume increase with respect to the disordered analog. A similar analysis has been conducted for the Li(1−3x)/2La(1+x)/2TiO3 and Na(1−3x)/2La(1+x)/2(Mg0.5W0.5)O3 solid solutions. These systems provide additional validation of the accuracy and versatility of the empirical modeling method used

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“…In this way, Δ r A can be used explicitly as a measure of A‐site ordering. Interestingly, while no evidence of long‐range A‐site ordering has been observed in the NLT system via x‐ray or neutron diffraction, this model clearly shows the pattern of errors leading to the conclusion of order. In fact, electron diffraction shows that the structure consists of nanodomains of order (short‐range order); thus, even short‐range order can be quantified with this model.…”

Section: Introductionmentioning

confidence: 69%

Empirical models for layered A‐site ordering in perovskite titanates

Smith

Ubic

2018

J Am Ceram Soc

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In industry and labs, predictive models describing processing-structure relationships are inherently valuable, yet few exist for cation ordering in perovskites. In this work, 15 compositions in the [(Na y Li 1−y ) (1−3x)/2 La (1+x)/2 ]TiO 3 (NLLT) system (y = 0.25, 0.5, and 0.75; x = 0, 0.0533, 0.1, 0.1733, and 0.225) were synthesized using a conventional solid-state mixed-oxide method. X-ray diffraction data show that some degree of long-range ordering of A-site cations exists for x ≥ 0.1, although electron-diffraction data indicate that short-range ordering exists even for x < 0.1, with the degree of ordering decreasing as the value of x increases. Empirical models have been derived for the A-site ordering parameter (η) as well as the resultant expansion (Δr A ) for each y series in the NLLT system, from which two general models were derived for perovskites with any arbitrary degree of 1:1 layered A-site ordering. These general models allow for the prediction of the order parameter and resulting expansion using only published ionic radii data.

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Structure and phase transition of Na_0.5La_0.5TiO₃

Cited by 17 publications

References 23 publications

Phonon-glass electron-crystal behaviour by A site disorder in n-type thermoelectric oxides

Phonon-glass electron-crystal behaviour by A site disorder in n-type thermoelectric oxides

Empirical Evidence for A‐Site Order in Perovskites

Empirical models for layered A‐site ordering in perovskite titanates

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