scholarly journals Assessment of Dynamic Structural Instabilities Across 24 Cubic Inorganic Halide Perovskites

Author(s):  
Ruo Xi Yang ◽  
Jonathan Skelton ◽  
E Lora Da Silva ◽  
Jarvist Moore Frost ◽  
Aron Walsh

<div><div>Metal halide perovskites are promising candidates for next-generation photovoltaic and optoelectronic applications. The flexible nature of the octahedral network introduces complexity when understanding their physical behavior. It has been shown that these materials are prone to decomposition, phase competition, and the local crystal structure often deviates from the average space group symmetry. To make stable phase-pure perovskites, understanding their structure-composition relations is of central importance. We demonstrate, from lattice dynamics calculations, that the 24 inorganic perovskites ABX<sub>3</sub> (A = Cs, Rb; B = Ge, Sn, Pb; X = F, Cl, Br, I) exhibit instabilities in their cubic phase. These instabilities include cation displacements, octahedral tilting, and Jahn-Teller distortions. The magnitudes of the instabilities vary depending on the chemical identity and ionic radii of the composition. The tilting instabilities are energetically dominant, and reduce as the tolerance factor increases, whereas cation displacements and Jahn-Teller type distortions depend on the interactions between the constituent ions. We further considered representative tetragonal, orthorhombic and monoclinic perovskites phases to obtain phonon-stable phases for each composition. This work provides insights into the thermodynamic driving force of the instabilities and will help guide synthesis in material screening. </div></div>

2019 ◽  
Author(s):  
Ruo Xi Yang ◽  
Jonathan Skelton ◽  
E Lora Da Silva ◽  
Jarvist Moore Frost ◽  
Aron Walsh

<div><div>Metal halide perovskites are promising candidates for next-generation photovoltaic and optoelectronic applications. The flexible nature of the octahedral network introduces complexity when understanding their physical behavior. It has been shown that these materials are prone to decomposition, phase competition, and the local crystal structure often deviates from the average space group symmetry. To make stable phase-pure perovskites, understanding their structure-composition relations is of central importance. We demonstrate, from lattice dynamics calculations, that the 24 inorganic perovskites ABX<sub>3</sub> (A = Cs, Rb; B = Ge, Sn, Pb; X = F, Cl, Br, I) exhibit instabilities in their cubic phase. These instabilities include cation displacements, octahedral tilting, and Jahn-Teller distortions. The magnitudes of the instabilities vary depending on the chemical identity and ionic radii of the composition. The tilting instabilities are energetically dominant, and reduce as the tolerance factor increases, whereas cation displacements and Jahn-Teller type distortions depend on the interactions between the constituent ions. We further considered representative tetragonal, orthorhombic and monoclinic perovskites phases to obtain phonon-stable phases for each composition. This work provides insights into the thermodynamic driving force of the instabilities and will help guide synthesis in material screening. </div></div>


2015 ◽  
Vol 654 ◽  
pp. 122-126 ◽  
Author(s):  
Carolina Mochales ◽  
Rolf Zehbe ◽  
Stefan Frank ◽  
Farzaneh Rahimi ◽  
Aleksandra Urbanska ◽  
...  

Zirconia-based ceramics have gained considerable interest for several applications (e.g. solid electrolytes in fuel cells and in oxygen sensors, thermal barrier coatings and biomaterials for dental and orthopaedic applications) due to their high mechanical strength, improved fracture toughness and easy affordability. Zirconia occurs in three crystal modifications at low-pressure conditions: monoclinic, tetragonal and cubic. The monoclinic phase is the natural room temperature stable phase, while the tetragonal and the cubic phase can be stabilized at room temperature by doping with the right amount of some oxide dopants (e.g. CaO, MgO, CeO2and Y2O3). The stabilization of the tetragonal phase results in a remarkable increase in mechanical toughness, whereas the stabilization of the cubic phase results in an increase of the ionic conductivity to values significantly higher than for other ceramics. In order to optimize the properties of the final ceramic by combining the high mechanical toughness of the tetragonal phase of zirconia together with the high ionic conductivity of its cubic phase, we established an EPD layering process with nanometric sized powders of Y-TZP with different mol percentages of yttrium oxide (3 % and 8 %) and produced multilayers of alternating tetragonal and cubic phases with a clearly defined interface. The crack propagation through this interface was studied by means of micro-indentation


2018 ◽  
Vol 08 (04) ◽  
pp. 1850024 ◽  
Author(s):  
Amantulla Mansuri ◽  
Ilyas Noor Bhatti ◽  
Imtiaz Noor Bhatti ◽  
Ashutosh Mishra

In the present study, we have synthesized polycrystalline samples of BaTi[Formula: see text]CoxO3 (BTCO) ([Formula: see text], 0.01, 0.03, 0.05, 0.07 and 0.10) with standard solid state reaction technique. The obtained samples are characterized by X-ray diffraction (XRD) and Raman spectroscopy for structural study. The detailed structural analysis has been performed by Rietveld refinement using Fullprof program. We observed an increase in lattice parameters, which results due to substitution of Co[Formula: see text] with large ionic radii (0.9[Formula: see text]Å) for smaller ionic radii (0.6[Formula: see text]Å) Ti[Formula: see text]. Moreover, peak at 45.5∘ shifts to 45∘ on Co doping, which is due to structure phase transition from tetragonal to cubic. Raman study infers that the intensity of characteristic peaks decreases and line width increases with Co doping. The bands linked with the tetragonal structure (305[Formula: see text]cm[Formula: see text]) decreased due to the tetragonal-to-cubic phase transition with Co doping. Our structural study reveals the expansion of BTCO unit cell and tetragonal-to-cubic phase transformation takes place. The results from different characterization techniques are conclusive and show structural evolution with Co doping. The samples are further characterized by dielectric spectroscopy, dielectric measurement reveals the increase of dielectric constant and transition [Formula: see text]C is observed for Barium titanate (BaTiO3), whereas transition disappears with Co doping. Both temperature and frequency-dependent tangent loss is also studied.


2021 ◽  
Author(s):  
Rebecca Scatena ◽  
Michał Andrzejewski ◽  
Roger Johnson ◽  
Piero Macchi

<div> <p><b>Through in-situ, high-pressure x-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub> undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct from previously reported Jahn-Teller switching in coordination polymers, which required at least two different ligands that crystallize in a reverse spectrochemical series. We show that the orbital reordering phase transition in [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub> is instead primarily driven by unconventional octahedral tilts and shifts in the framework, and/or a reconfiguration of A-site cation ordering. These structural instabilities are unique to the coordination polymer perovskites, and may form the basis for undiscovered orbital reorientation phenomena</b><b> in this broad family of materials.</b><b></b></p> </div> <b><br></b>


CrystEngComm ◽  
2019 ◽  
Vol 21 (9) ◽  
pp. 1389-1396 ◽  
Author(s):  
Zhuo Chen ◽  
Lvming Dong ◽  
Hanchuan Tang ◽  
Yan Yu ◽  
Lei Ye ◽  
...  

One-dimensional all-inorganic halide perovskites have emerged as one of the most prominent materials in the application of optoelectronic devices due to their remarkable properties such as a low number of defects, morphological anisotropy, mechanical flexibility and fast charge transfer capability.


2012 ◽  
Vol 26 (04) ◽  
pp. 1150025 ◽  
Author(s):  
MINPING ZHANG ◽  
GUANGTAO WANG

The electronic, magnetic and orbital structures of KCrF 3 in the cubic phase are studied by first principles method. In the cubic phase, the three Cr - F bonds distance are equal. If the Jahn–Teller distortion is the origin of the orbital polarization, the orbital ordering would disappear. However, our theoretical calculations show that the orbital ordering exists even without the Jahn–Teller distortion. By studying how the orbital polarization changes with the electron correlation and the Jahn–Teller distortion, we found that the origin of the orbital polarization should be the electron correlation and the Jahn–Teller distortion can reinforced such polarization.


2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Mantas Simenas ◽  
Sergejus Balciunas ◽  
Jacob N. Wilson ◽  
Sarunas Svirskas ◽  
Martynas Kinka ◽  
...  

Abstract Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.


2021 ◽  
Author(s):  
Rebecca Scatena ◽  
Michał Andrzejewski ◽  
Roger Johnson ◽  
Piero Macchi

<div> <p><b>Through in-situ, high-pressure x-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub> undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct from previously reported Jahn-Teller switching in coordination polymers, which required at least two different ligands that crystallize in a reverse spectrochemical series. We show that the orbital reordering phase transition in [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]Cu(HCOO)<sub>3</sub> is instead primarily driven by unconventional octahedral tilts and shifts in the framework, and/or a reconfiguration of A-site cation ordering. These structural instabilities are unique to the coordination polymer perovskites, and may form the basis for undiscovered orbital reorientation phenomena</b><b> in this broad family of materials.</b><b></b></p> </div> <b><br></b>


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