Structural studies of the high temperature phases of AgTaO3

Farid, Umair; Khan, Hidayat Ullah; Avdeev, Maxim; Injac, Sean; Kennedy, Brendan J.

doi:10.1016/j.jssc.2017.12.023

Cited by 17 publications

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References 30 publications

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“…Above the T = 182 K crystallographically unresolvable phase transition, the ratio of ν Q for the two signals depends linearly on the magnitude of the crystallographic tetragonal compression, quantified as the ratio of the lattice parameters c tet / a tet (Figure b). We note that the tetragonal compression of the unit cell ( c / a < 1 ) necessitates a large compression of the apical lead–bromide bonds relative to the shrinking of a tet / due to the octahedral tilting, akin to the P 4/ mbm phase of AgTaO 3 and the pseudotetragonal Imma phase of SrZrO 3 . , Below 182 K the higher frequency peak assigned to the c axis bromide in the NQR spectra begins to decrease in frequency. As the ratio of the nuclear quadrupolar frequencies deviates from a linear relationship with the c tet / a tet ratio, contraction of the inorganic framework is insufficient to explain the data.…”

Section: Resultsmentioning

confidence: 83%

“…We note that the tetragonal compression of the unit cell (c/a < 1) necessitates a large compression of the apical lead−bromide bonds relative to the shrinking of a tet / 2 due to the octahedral tilting, akin to the P4/mbm phase of AgTaO 3 and the pseudotetragonal Imma phase of SrZrO 3 . 50,51 Below 182 K the higher frequency peak assigned to the c axis bromide in the NQR spectra begins to decrease in frequency. As the ratio of the nuclear quadrupolar frequencies deviates from a linear relationship with the 2 c tet / a tet ratio, contraction of the inorganic framework is insufficient to explain the data.…”

Section: ■ Resultsmentioning

confidence: 99%

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Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

et al. 2020

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Although initial studies on hybrid perovskites for photovoltaic applications focused on simple compositions, the most technologically relevant perovskites are heavily substituted. The influence of chemical substitution on the general phase behavior and specific physical properties remains ambiguous. The hybrid perovskite formamidinium lead bromide, CH(NH2)2PbBr3, exhibits complex phase behavior manifesting in a series of crystallographically-unresolvable phase transitions associated with changes in the cation dynamics. Here, we characterize the molecular and lattice dynamics of CH(NH2)2PbBr3 as a function of temperature, and their evolution upon chemical substitution of CH(NH2)2 + for cesium (Cs + ) with crystallography, neutron scattering, 1 H and 14 N nuclear magnetic resonance spectroscopy, and 79 Br nuclear quadrupolar spectroscopy. Cs + substitution suppresses the four low-temperature phase transitions of CH(NH2)2PbBr3, which propagate through concerted changes in the dynamic degrees of freedom of the organic sub-lattice and local or long-range distortions of the octahedral framework. We propose that cesium substitution suppress the phase transitions through the relief of geometric frustration associated ** Both authors contributed equally.with the orientations of CH(NH2)2 + molecules, which retain their local dynamical degrees of freedom.

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Section: Resultsmentioning

confidence: 83%

Section: ■ Resultsmentioning

confidence: 99%

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

et al. 2020

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“…Analogous to AN, the AgTaO 3 (AT) material possesses numerous phase transitions as a function of temperature, with room temperature rhombohedral phase 18 , 33 . Of particular significance is that AN and AT have the infinite miscibility thus (1- x )AgNbO 3 - x AgTaO 3 (ANT x ) solid solution can be formed with the addition of AgTaO 3 in AgNbO 3 , leading to successive physical property transformations, such as phase transition sequence and dielectric permittivity depending on solid solution composition 34 .…”

Section: Introductionmentioning

confidence: 99%

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency

et al. 2020

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Dielectric capacitors with high energy storage density (Wrec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high Wrec of 6.3 J cm-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2–M3 phase boundary in (1-x)AgNbO3-xAgTaO3 solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20–150 °C and excellent cycling reliability up to 106 cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.

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“…15 The same high-temperature phases are observed in AgTaO 3 . 21 Although the temperature dependence of the structure of AgNbO 3 is not as complex as that of NaNbO 3 , it is noticeably more complex than that of other perovskite systems such as CaTiO 3 , SrZrO 3 , NaTaO 3 , and PrAlO 3 . 22−26 The identification of the room-temperature polar structure of AgNbO 3 has proved problematic.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The situation for AgNbO 3 is less well-established; however, this also undergoes a complex series of phase transitions upon heating. − While the details of the low-temperature structures in AgNbO 3 are still controversial, it is well-established that NaNbO 3 and AgNbO 3 undergo the same high-temperature structural transitions, Cmcm → P 4/ mbm → Pm 3̅ m , where these phases are labeled for AgNbO 3 as O, T, and C respectively . The same high-temperature phases are observed in AgTaO 3 . Although the temperature dependence of the structure of AgNbO 3 is not as complex as that of NaNbO 3 , it is noticeably more complex than that of other perovskite systems such as CaTiO 3 , SrZrO 3 , NaTaO 3 , and PrAlO 3 . − …”

Section: Introductionmentioning

confidence: 99%

Impact of Li Doping on the Structure and Phase Stability in AgNbO₃

2020

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The impact of Li doping on the temperature-induced phase transitions in silver niobates Ag1–x Li x NbO3 has been investigated using a combination of high-resolution powder neutron diffraction and synchrotron X-ray diffraction. Considering both the cell metric and distortions of the NbO6 octahedra, estimated by Rietveld refinements, it is shown that the sequence of temperature-induced phases in AgNbO3 is P21 am → Pcam → Cmcm → P4/mbm → Pm3̅m. This sequence is simpler than that proposed in earlier studies. Evidence is presented for a second-order Jahn–Teller distortion in the Pcam phase. At x > 0.05, Li doping favors the formation of a rhombohedral phase in space group R3c, and such samples display the temperature-induced sequence R3c → Pbnm → Cmcm → P4/mbm → Pm3̅m. Unusual volume changes associated with the phase transitions point to the potential importance of lattice matching in optimizing the properties of thin films of doped AgNbO3.

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Structural studies of the high temperature phases of AgTaO3

Cited by 17 publications

References 30 publications

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency

Impact of Li Doping on the Structure and Phase Stability in AgNbO₃

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Structural studies of the high temperature phases of AgTaO3

Cited by 17 publications

References 30 publications

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency

Impact of Li Doping on the Structure and Phase Stability in AgNbO3

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Impact of Li Doping on the Structure and Phase Stability in AgNbO₃