Large low-temperature specific heat in pyrochlore<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Bi</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>Ti</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>

Melot, Brent C.; Tackett, Ronald; O’Brien, J. R.; Hector, Andrew L.; Lawes, G.; Seshadri, Ram; Ramirez, A. P.

doi:10.1103/physrevb.79.224111

Cited by 56 publications

(51 citation statements)

References 24 publications

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“…The heat capacity of the crystal deviates substantially from the ∼T 3 scaling predicted by the Debye model at low temperatures, as indicated by the low temperature "hump" in the C/T 3 versus T plot. 30,31 Systems with glassy disorder are well-known to exhibit heat ca- The broader hump in C/T 3 for HC(NH 2 ) 2 PbI 3 is consistent with our assertion that this compound exhibits greater glass fragility than CH 3 NH 3 PbI 3 . 30 Liu and Löhneysen have compiled the maximum of C/T 3 and the corresponding temperature for a variety of amorphous and crystalline solids, and determined a scaling relation between these two parameters.…”

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confidence: 88%

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Fabini

Hogan

Evans

et al. 2016

J. Phys. Chem. Lett.

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126

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Hybrid main group halide perovskites hold great technological promise in optoelectronic applications and present rich and complex evolution of structure and dynamics. Here we present low-temperature dielectric measurements and calorimetry of APbI3 [A = CH3NH3 +, HC(NH2)2 +] that suggest glassy behavior on cooling. In both compounds, the dielectric loss displays frequency-dependent peaks below 100 K characteristic of a glassy slowing of relaxation dynamics, with HC(NH2)2PbI3 exhibiting greater glass fragility. Consistent with quenched disorder, the low-temperature heat capacity of both perovskites deviates substantially from the ∼T 3 acoustic phonon contribution predicted by the Debye model. We suggest that static disorder of the A-site molecular cation, potentially coupled to local distortions of the Pb–I sublattice, is responsible for these phenomena. The distinct low-temperature dynamics observed in these two perovskites suggest qualitative differences in the interaction between the molecular cation and the surrounding inorganic framework, with potential implications for defect screening and device performance at ambient temperatures.

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confidence: 88%

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Fabini

Hogan

Evans

et al. 2016

J. Phys. Chem. Lett.

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111

126

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“…A number of more traditional crystalline materials also exhibit similar low temperature peaks in C∕T 3 plots. Such plots have been used to explore the nature of vibrations and disorders in materials such as quartz SiO 2 and the pyrochlore Bi 2 Ti 2 O 7 (16). In the present case, the C∕T 3 plot for the DMAZF also revealed a well-defined broad peak at 25 K (Fig.…”

mentioning

confidence: 60%

Mechanism of the order–disorder phase transition, and glassy behavior in the metal-organic framework [(CH ₃ ) ₂ NH ₂ ]Zn(HCOO) ₃

Besara

Jain

Dalal

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

194

117

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Transitions associated with orientational order-disorder phenomena are found in a wide range of materials and may have a significant impact on their properties. In this work, specific heat and 1 H NMR measurements have been used to study the phase transition in the metal-organic framework (MOF) compound ½ðCH 3 Þ 2 NH 2 ZnðHCOOÞ 3 . This compound, which possesses a perovskite-type architecture, undergoes a remarkable order-disorder phase transition at 156 K. The ðCH 3 Þ 2 NH þ 2 (DMA þ ) cationic moieties that are bound by hydrogen bonds to the oxygens of the formate groups (N─H⋯O ∼ 2.9 Å) are essentially trapped inside the basic perovskite cage architecture. Above 156 K, it is the orientations of these moieties that are responsible for the disorder, as each can take up three different orientations with equal probability. Below 156 K, the DMA þ is ordered within one of these sites, although the moiety still retains a considerable state of motion. Below 40 K, the rotational motions of the methyl groups start to freeze. As the temperature is increased from 4 K in the NMR measurements, different relaxation pathways can be observed in the temperature range approximately 65-150 K, as a result of a "memory effect." This dynamic behavior is characteristic of a glass in which multiple states possess similar energies, found here for a MOF. This conclusion is strongly supported by the specific heat data.multiferroic | organic-inorganic solids M etal-organic framework (MOF) compounds are extended organic-inorganic crystalline solids in well-defined geometric structures (1, 2). Because of the exciting possibility of dynamic and related behavior with advanced device applications, considerable effort is currently being devoted to creating previously undescribed MOF compounds (3, 4). We recently reported a series of multifunctional MOF compounds that simultaneously exhibit ferromagnetic and ferroelectric behavior associated with orientational ordering (5, 6). These compounds possess the perovskite structure, ABX 3 , with A as the dimethylammonium cation ðCH 3 Þ 2 NH þ 2 , DMA þ ; B as a divalent transition metal ion (Zn 2þ , Mn 2þ , Ni 2þ , Fe 2þ , etc.), and X as the formate ion HCO − 2 (5, 6). Because many of the inorganic perovskites are ferroelectrics, it was interesting to find these analogous MOF compounds to also exhibit ferroelectric behavior, but the microscopic mechanism of the onset of ferroelectricity and the concomitant solid/solid-phase transition was not fully understood (5, 6). A clue to the mechanism is provided by the molecular structure. X-ray studies show that ½ðCH 3 Þ 2 NH 2 ZnðHCOOÞ 3 (henceforth DMAZF) has the basic perovskite architecture in which the metal atoms are located at the corners of a cube and are connected via the oxygen atoms of formate linkers (Zn─O─CH─O─Zn) (Fig. 1) (6, 7). The DMA þ cation is located in the cavity and is hydrogen-bonded to the formate frame via its amino H atoms to the formate O atoms, and-in analogy with the antiferroelectric phase transition in NH 4 H 2 PO 4 -the making ...

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“…The electronic structure of Bi 2 Ti 2 O 6 OЈ from DFT calculations has been reported previously 4,5,7 and so only a brief description of the electronic structure is given here. In common with previous work on Bi 2 Ti 2 O 6 OЈ, 4,5 we find a group of bands at the bottom of the valence band which has mainly Bi 6s character.…”

Section: B Electronic Structurementioning

confidence: 99%

“…[4][5][6][7] The ideal pyrochlore structure belongs to the Fd3m space group and consists of interpenetrating Bi 2 OЈ and Ti 2 O 6 polyhedral networks. Both experimental and theoretical studies of Bi 2 Ti 2 O 6 OЈ ͑Refs.…”

Section: Introductionmentioning

confidence: 99%

“…The cause of the displacement of the O ions from the SiSi axis in ␤ cristobalite is clearly the stereochemical arrangement of two SiO bonds and two off-center O lone pairs. The cause of the Bi displacement in Bi 2 Ti 2 O 6 OЈ has been discussed in terms of offcentering of the Bi 6s lone pair 4,5,7 or a soft polar phonon mode 6 but the cause of displacement is not as clear as in SiO 2 . The ratio of ionic radii in Bi 2 Ti 2 O 6 OЈ, r A / r B = 1.93, 2 lies outside the usual stability range for pyrochlores ͑1.46-1.78͒ at atmospheric pressure 15 and so some lattice instability might be expected.…”

Section: Introductionmentioning

confidence: 99%

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First-principles calculation of the structure and dielectric properties ofBi2Ti2O7

Patterson

2010

Phys. Rev. B

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The structure, vibrational modes, and phonon contribution to the dielectric function of the pyrochlore Bi 2 Ti 2 O 6 OЈ were calculated using first-principles methods. Total-energy minimization calculations were performed for Bi 2 Ti 2 O 6 OЈ in a unit cell containing 88 ions, which had the ideal, cubic pyrochlore structure as the initial configuration. No symmetry constraints were imposed during this relaxation. Subsequent symmetry analysis of the relaxed structure found Pna2 1 space-group symmetry in a 44 ion unit cell. This structure contains Bi ions with two types of eightfold coordination by O and OЈ ions. Vibrational modes and the dielectric function were calculated for the Fd3m, Pna2 1 , and P 1 structures. The crystal structure obtained by total-energy minimization is compared to structural data from reverse Monte Carlo analysis of neutron total scattering data. The imaginary part of the dielectric function derived from vibrational mode calculations is compared to dielectric function data for several related pyrochlores. Phonons which make the largest contributions to the dielectric constant are identified and analyzed.

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Large low-temperature specific heat in pyrochloreBi2Ti2O7

Cited by 56 publications

References 24 publications

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Mechanism of the order–disorder phase transition, and glassy behavior in the metal-organic framework [(CH ₃ ) ₂ NH ₂ ]Zn(HCOO) ₃

First-principles calculation of the structure and dielectric properties ofBi2Ti2O7

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Large low-temperature specific heat in pyrochloreBi2Ti2O7

Cited by 56 publications

References 24 publications

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH3NH3PbI3 and HC(NH2)2PbI3

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH3NH3PbI3 and HC(NH2)2PbI3

Mechanism of the order–disorder phase transition, and glassy behavior in the metal-organic framework [(CH 3 ) 2 NH 2 ]Zn(HCOO) 3

First-principles calculation of the structure and dielectric properties ofBi2Ti2O7

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Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃

Mechanism of the order–disorder phase transition, and glassy behavior in the metal-organic framework [(CH ₃ ) ₂ NH ₂ ]Zn(HCOO) ₃