Double Double Cation Order in the High‐Pressure Perovskites MnRMnSbO6

Cation ordering in ABO₃ perovskites adds to their chemical variety and can lead to properties such as ferrimagnetism and magnetoresistance in Sr₂FeMoO₆. Through high‐pressure and high‐temperature synthesis, a new type of “double double perovskite” structure has been discovered in the family MnRMnSbO₆ (R=La, Pr, Nd, Sm). This tetragonal structure has a 1:1 order of cations on both A and B sites, with A‐site Mn²⁺ and R³⁺ cations ordered in columns and Mn²⁺ and Sb⁵⁺ having rock salt order on the B sites. The MnRMnSbO₆ double double perovskites are ferrimagnetic at low temperatures with additional spin‐reorientation transitions. The ordering direction of ferrimagnetic Mn spins in MnNdMnSbO₆ changes from parallel to [001] below T_C=76 K to perpendicular below the reorientation transition at 42 K at which Nd moments also order. Smaller rare earths lead to conventional monoclinic double perovskites (MnR)MnSbO₆ for Eu and Gd.     

Large Magnetization and Frustration Switching of Magnetoresistance in the Double‐Perovskite Ferrimagnet Mn2FeReO6

Ferrimagnetic A₂BB′O₆ double perovskites, such as Sr₂FeMoO₆, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn₂FeReO₆, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μ_B which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn²⁺ spin ordering which cants Fe³⁺ and Re⁵⁺ spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn²⁺ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.     

Crystal Structure and Property of Perovskite-Type Oxides Containing Ion Vacancy

Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K₂NiF₄ compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr₂(Sr_1-xM_x)TaO_6-d (M = Ca²⁺ and Nd³⁺) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr_2-xLa_xCo_1-yTa_1+yO₆ and oxygen-deficient Sr_2-xLa_xMg_1-yTa_1+yO_6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size.     

Room‐Temperature Ferroelectric Material Composed of a Two‐Dimensional Metal Halide Double Perovskite for X‐ray Detection

Although two‐dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room‐temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room‐temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)₄AgBiBr₈, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm^?2, triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr₆/BiBr₆ octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility‐lifetime product (μτ=1.0×10^?3 cm² V^?1) for detecting X‐ray photons, which is almost tenfold higher than that of CH₃NH₃PbI₃ wafers. As far as we know, this is the first study on an X‐ray‐sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.     

Room-Temperature Ferroelectric Material Composed of a Two-Dimensional Metal Halide Double Perovskite for X-ray Detection

Although two-dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room-temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room-temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)₄AgBiBr₈, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm⁻², triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr₆/BiBr₆ octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility-lifetime product (μτ=1.0×10⁻³ cm² V⁻¹) for detecting X-ray photons, which is almost tenfold higher than that of CH₃NH₃PbI₃ wafers. As far as we know, this is the first study on an X-ray-sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.     

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH3NH3PbI3

Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH₃NH₃PbI₃ being an archetypal compound. The question why CH₃NH₃PbI₃ has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non‐centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long‐range level. Although the molecular cation CH₃NH₃⁺ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions.     

Bulk Mn2+ Doped 1D Hybrid Lead Halide Perovskite with Highly Efficient,Tunable and Stable Broadband Light Emissions

Mn²⁺ doped colloidal three-dimensional (3D) lead halide perovskite nanocrystal (PNC) has attracted intensive research attention; however, the low exciton binding energy and fatal optical instability of 3D PNC seriously hinder the optoelectronic application. Therefore, it remains significant to explore new stable host perovskite with strongly bound exciton to realize more desirable luminescent property. In this work, we utilized bulk one-dimensional (1D) hybrid perovskite of [AEP]PbBr₅ ⋅ H₂O (AEP=N-aminoethylpiperazine) as structural platform to rationally optimize the luminescent property by a controllable Mn²⁺ doping strategy. Significantly, the series of Mn²⁺-doped 1D [AEP]PbBr₅ ⋅ H₂O show enhanced energy transfer efficiency from the strongly bound excitons of host material to 3d electrons of Mn²⁺ ions, resulting in tunable broadband light emissions from weak yellow to strong red spectral range with highest photoluminescence quantum yield up to 28.41 %. More importantly, these Mn²⁺-doped 1D perovskites display ultrahigh structural and optical stabilities in humid atmosphere, water and high temperature exceeding the conventional 3D PNC. Combined highly efficient, tunable and stable broadband light emissions enable Mn²⁺-doped 1D perovskite as excellent down-converting phosphor showcasing the potential application in white light emitting diode. This work not only provides a profound understanding of low-dimensional perovskites but also opens a new way to rationally design high-performance broadband light emitting perovskites for solid-state lighting and displaying devices.     

Crystal structures of disordered A2Mn3+M5+O6 (A=Sr,Ca; M=Sb,Nb, Ru) perovskites

Polycrystalline samples of A₂MnMO₆ (A=Sr, Ca; M=Nb, Sb, Ru) were prepared by conventional solid state synthesis and their crystal structures were determined using neutron powder diffraction data. All six compounds can be classified as distorted, disordered perovskites. The Mn³⁺/M⁵⁺ distribution is disordered in all six compounds. The strontium containing compounds, Sr₂MnMO₆ (M=Nb, Sb, Ru), undergo out of phase rotations of the octahedra about the c-axis (tilt system a⁰a⁰c⁻) leading to tetragonal I4/mcm space group symmetry. The calcium containing compounds, Ca₂MnMO₆ (M=Nb, Ru, Sb), have orthorhombic Pnma space group symmetry, as a result of a GdFeO₃-type octahedral tilting distortion (tilt system a⁻b⁺a⁻). A cooperative Jahn–Teller distortion is observed in Sr₂MnSbO₆ and Sr₂MnRuO₆, but it is much smaller than the distortion observed in LnMnO₃ (Ln=lanthanide ion) perovskites. It is possible that Jahn–Teller distortions of the MnO₆ octahedra take place on a short-range length scale in the other four compounds, but there is little or no evidence for cooperative ordering of the local distortions. These findings demonstrate a link between orbital ordering, cation ordering and octahedral tilting.     

A Pressure‐Induced Inverse Order–Disorder Transition in Double Perovskites

Given the consensus that pressure improves cation ordering in most of known materials, a discovery of pressure‐induced disordering could require recognition of an order–disorder transition in solid‐state physics/chemistry and geophysics. Double perovskites Y₂CoIrO₆ and Y₂CoRuO₆ polymorphs synthesized at 0, 6, and 15 GPa show B‐site ordering, partial ordering, and disordering, respectively, accompanied by lattice compression and crystal structure alteration from monoclinic to orthorhombic symmetry. Correspondingly, the long‐range ferrimagnetic ordering in the B‐site ordered samples are gradually overwhelmed by B‐site disorder. Theoretical calculations suggest that unusual unit‐cell compressions under external pressures unexpectedly stabilize the disordered phases of Y₂CoIrO₆ and Y₂CoRuO₆.     

The tunnel manganese oxide Na4.32Mn9O18: a new Na+ site discovered by single‐crystal X‐ray diffraction

The title compound, tetrasodium nonamanganese octadecaoxide, Na_4.32Mn₉O₁₈, was synthesized by reacting Mn₂O₃ with NaCl. One Mn atom occupies a site of 2/m symmetry, while all other atoms sit on mirror planes. The compound is isostructural with Na₄Ti₄Mn₅O₁₈ and suggestive of Mn³⁺/Mn⁴⁺ charge ordering. It has a double‐tunnel structure built up from double and triple chains of MnO₆ octahedra and single chains of MnO₅ square pyramids by corner sharing. Disordered Na⁺ cations occupy four crystallographic sites within the tunnels, including an unexpected new Na⁺ site discovered inside the large S‐shaped tunnel. A local‐ordering model is used to show the possible Na⁺ distribution, and the unit‐cell evolution during charging/discharging is explained on the basis of this local‐ordering model.     

Influence of Co doping on properties of Pr0.8Na0.2Mn(1−y)CoyO3 perovskites

The influence of the cobalt substitution for manganese ions in the series of the perovskites Pr_0.8Na_0.2Mn_(1−x)Co_xO₃ (0?x?0.1) was investigated. The study of electric and magnetic properties was carried out on sintered polycrystalline samples. The composition of x=0.04 exhibits an insulator to metal-like (I-M) transition at ∼106 K, connected with a ferromagnetic arrangement. For x=0.1, however, an insulating behavior persists down to low temperatures in spite of the transition to the bulk ferromagnetism. The observed properties are related to an acting of the cobalt ions as point defects. They disturb the tendency to charge ordering and instead of the antiferromagnetic arrangement typical for x=0 ferromagnetic double-exchange interactions Mn³⁺-O²⁻-Mn⁴⁺ and Mn^3.5+δ-O²⁻-Co²⁺, decisive for the resulting behavior, arise.     

Reentrant Structural Transitions and Collapse of Charge and Orbital Orders in Quadruple Perovskites

Charge and orbital degrees of freedom determine properties of many materials, and are central to many important phenomena. At high temperatures, thermal fluctuations overcome them, and high‐symmetry structures are realized. On decreasing temperature, different charge‐ and orbital‐order transitions take place accompanied by symmetry lowering. Remarkable exceptions to this general tendency, realized in Cu‐doped BiMn₇O₁₂ quadruple perovskites, are presented. Introduction of Cu²⁺ produces mixtures of Mn³⁺ and Mn⁴⁺ and charge degree of freedom. BiCuMn₆O₁₂ (and compositions in the vicinity) exhibits well‐defined 1:3 charge order of Mn⁴⁺ and Mn³⁺ and orbital order of Mn³⁺ near room temperature, but both charge and orbital orders collapse below about 115 K with the reentrance of the high‐temperature cubic Im phase. What is interesting the collapse can be controlled by a magnetic field even without long‐range magnetic order, and the collapsed phase shows nearly zero thermal expansion.     

Charge disorder effects in 3d transition metal oxide perovskites

The effects of the random electrostatic potential due to differences in formal charge between A site R³⁺ (lanthanide, Y), M²⁺ (Ca, Sr, Ba) and Th⁴⁺ cations have been investigated in ferromagnetic AMnO₃ and superconducting A₂CuO₄ perovskites. Series of samples in which the mean A site charge and the mean and variance of the A cation radius distribution are held constant, but the A site charge variance increases, show no significant changes of the electronic (Curie or superconducting) transition temperatures. The effect of the A cation random potentials on electronic transitions in the 3d metal oxide perovskites are insignificant in comparison to the lattice effects from the differing cation sizes.     

High pressure synthesis and crystal structure of a new series of perovskite-like compounds CMn7O12 (C = Na,Ca, Cd,Sr, La,Nd)

A new series of perovskite-like compounds CMn₇O₁₂ have been synthesized under high pressure and high temperature conditions. C is a large divalent or trivalent cation such as Ca, Cd, Sr, La and Nd. The structures of the quenched materials have been determined from powder X-ray data. They are distortions of the NaMn₇O₁₂ cubic structure. The [C²⁺Mn³⁺₃](Mn³⁺₃Mn⁴⁺)O₁₂ compounds are trigonal ($\text{R}\text{3}$). The C²⁺ and Mn³⁺ as well as the Mn³⁺ and Mn⁴⁺ cations are ordered on the corresponding A and B sites of the perovskite structure, respectively. The [C³⁺Mn³⁺₃] (Mn³⁺₄)O₁₂ compounds are monoclinic ($\text{I}\text{2}\text{m}$). In these compounds the order exists only in the A sites. It is shown that the lower symmetry may be the result of a cooperative Jahn-Teller effect of the Mn³⁺ cations occupying the B sites.     

Achieving Color-Tunable Long Persistent Luminescence in Cs2CdCl4 Ruddlesden-Popper Phase Perovskites

Two-dimensional (2D)-halide perovskites have been enriched over recent years to offer remarkable features from diverse chemical structures and environmental stability endowed with exciting functionalities in photoelectric detectors and phosphorescence systems. However, the low conversion efficiency of singlet to triplet in 2D hybrid halide perovskites reduces phosphorescence lifetimes. In this study, the long persistent luminescence of 2D all-inorganic perovskites with a self-assembled 2D interlayer galleries structure is investigated. The results show that the decay time of the long persistent luminescence increases from 450 s to 600 s, and the luminescence color changes from cyan to orange, and the thermal stability of photoluminescence enhances dramatically after replacing Cd²⁺ by appropriate Mn²⁺ ions in 2D Cs₂CdCl₄ Ruddlesden-Popper phase perovskites. Furthermore, diversified anti-counterfeiting modes are fabricated to highlight the promising applications of Cs₂CdCl₄ perovskite systems with tunable persistent luminescence in advanced anti-counterfeiting. Therefore, our studies provide a novel model for realizing tunable long persistent luminescence of perovskite with 2D self-assembled layered structure for advanced anti-counterfeiting.     

Coexistence of magnetic and electric orderings in a divalent Cr2+-based multiaxial molecular ferroelectric

Multiferroic materials have attracted great interest because of their underlying new science and promising applications in data storage and mutual control devices. However, they are still very rare and highly imperative to be developed. Here, we report an organic–inorganic hybrid perovskite trimethylchloromethylammonium chromium chloride (TMCM–CrCl₃), showing the coexistence of magnetic and electric orderings. It displays a paraelectric–ferroelectric phase transition at 397 K with an Aizu notation of 6/mFm, and spin-canted antiferromagnetic ordering with a Néel temperature of 4.8 K. The ferroelectricity originates from the orientational ordering of TMCM cations, and the magnetism is from the [CrCl₃]⁻ framework. Remarkably, TMCM–CrCl₃ is the first experimentally confirmed divalent Cr²⁺-based multiferroic material as far as we know. A new category of hybrid multiferroic materials is pointed out in this work, and more Cr²⁺-based multiferroic materials will be expectedly developed in the future.

An organic–inorganic hybrid perovskite Trimethylchloromethylammonium chromium(ii) chloride (TMCM–CrCl₃) can simultaneously show excellent ferroelectricity and antiferromagnetism, which is the first experimentally confirmed Cr²⁺-based multiferroic material.     

Tailored Engineering of an Unusual (C4H9NH3)2(CH3NH3)2Pb3Br10 Two‐Dimensional Multilayered Perovskite Ferroelectric for a High‐Performance Photodetector

Two‐dimensional (2D) layered hybrid perovskites have shown great potential in optoelectronics, owing to their unique physical attributes. However, 2D hybrid perovskite ferroelectrics remain rare. The first hybrid ferroelectric with unusual 2D multilayered perovskite framework, (C₄H₉NH₃)₂(CH₃NH₃)₂Pb₃Br₁₀ ( 1 ), has been constructed by tailored alloying of the mixed organic cations into 3D prototype of CH₃NH₃PbBr₃. Ferroelectricity is created through molecular reorientation and synergic ordering of organic moieties, which are unprecedented for the known 2D multilayered hybrid perovskites. Single‐crystal photodetectors of 1 exhibit fascinating performances, including extremely low dark currents (ca. 10⁻¹² A), large on/off current ratios (ca. 2.5×10³), and very fast response rate (ca. 150 μs). These merits are superior to integrated detectors of other 2D perovskites, and compete with the most active CH₃NH₃PbI₃.     

Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb,Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Thin films of A-site co-substituted, PbTiO₃ (PTO) by Ba²⁺ and Ca²⁺, i.e., PBCT70, PBCT60, PBCT50 and PBCT40 were fabricated on Pt/Ti/SiO₂/Si substrates by chemical solution deposition. Structures of the samples were investigated from the viewpoint of local-, medium- and long-range order by X-ray absorption near structure (XANES), micro-Raman and infrared spectroscopies and by X-ray diffraction (XRD). The films thickness were determined by using field-emission scanning electron microscope. The experimental results demonstrate that BaO₁₂ clusters are the critical dominant ferroelectricity cause in PBCT thin films rather than CaO₁₂ clusters. XRD analysis which was applied to investigate the crystal symmetry indicates the absence of long-range structural distortion for samples at higher concentrations of Ba²⁺ and Ca²⁺. However, an analysis of structural medium- and local-range order such as infrared, micro-Raman and XANES spectroscopies revealed that symmetry changes are much more prominent; i.e., local structural distortions remain. Temperature-dependent dielectric permittivity measurements confirmed a decreasing ferroelectric-to-paraelectric phase transition temperature and showed a broad phase transition with an increase in BaO₁₂ and CaO₁₂ clusters. In addition, the lack of long-range polar ordering for the ferroelectric dipole caused by symmetry changes decreases the remanent polarization.     

A Quasi-Two-Dimensional Trilayered CsPbBr3-based Dion-Jacobson Hybrid Perovskite toward High-Performance Photodetection

Quasi-two-dimensional (Q-2D) Dion-Jacobson (DJ) organic-inorganic hybrid perovskites based on CsPbBr₃ are promising candidates for photodetection. Previous studies have predicted that the photoresponse of such materials with high inorganic-layer numbers (n) will be more protruding in this portfolio. However, until now, only bilayered (n=2) CsPbBr₃-based DJ-type hybrid perovskites are obtained and the higher number of layers (n>2) remain completely unexplored, owing to the relatively high formation energies. Here, by incorporating diamine into the 3D CsPbBr₃ motif, a new Q-2D trilayered CsPbBr₃-based DJ-type hybrid perovskite that contains organic cation and inorganic Cs metal, namely (4-AMP)Cs₂Pb₃Br₁₀ ( 1 , 4-AMP²⁺=4-(aminomethyl)piperidinium, n=3), is obtained. Excitingly, 1 exhibits excellent photoresponse, superior to its single-layered and bilayered counterparts. The resulting photodetectors thus exhibit a large on/off ratio (>10³), high photodetectivity (6.5×10¹⁰ Jones) and fast response speed (193 μs). As far as we know, 1 is the first Q-2D CsPbBr₃-based DJ-type hybrid perovskites with high n numbers. Our results may widen the range of the potential material in application of photodetection and will be helpful to design hybrid perovskites for other advanced optoelectronic devices.     

AxMn1-xFe2O4铁氧体(A=Zn,Ni)中阳离子的占位有序化行为研究

基于尖晶石晶体结构信息,本文采用热力学三亚晶格模型,将材料热力学计算和第一性原理计算相结合,研究了Zn_xMn_1-x Fe₂O₄和Ni_xMn_1-xFe₂O₄立方相中的Zn²⁺、Ni²⁺、Mn²⁺以及Fe³⁺在8a和16d亚晶格上的占位有序化行为。结果表明:在锰铁氧体中,室温下Mn²⁺完全占据在8a亚晶格上,Fe³⁺完全占据在16d亚晶格上,属于正尖晶石结构;随着热处理温度升高,在1 273 K达到热处理平衡时的占位构型为(Fe_0.09³⁺Mn_0.91²⁺)[Fe_1.91³⁺Mn_0.09²⁺]O₄,在热处理温度升至1 473 K时,达到热处理平衡时的占位构型为(Fe_0.11³⁺ Mn_0.89²⁺)[Fe_1.89³⁺Mn_0.11²⁺]O₄,均与实验结果符合较好。在锌铁氧体中,室温下Zn²⁺完全占据在8a亚晶格上,Fe³⁺完全占据在16d亚晶格上,属于正尖晶石结构;在热处理温度较高时,Zn²⁺和Fe³⁺发生部分置换,符合实验结果。在镍铁氧体中,半数的Fe³⁺在室温下占据在8a亚晶格上,Ni²⁺与剩下另一半的Fe³⁺共同占据在16d亚晶格上,仅在热处理温度较高的时候发生微弱变化,亦与已有的实验结果吻合。在此基础上,本文进一步通过热力学预测建立了立方相尖晶石结构的Zn_xMn_1-xFe₂O₄、Ni_xMn_1-xFe₂O₄复合体系中阳离子占位行为与热处理温度对占位的影响。