Structural phase transitions in perovskite compounds based on diatomic or multiatomic bridges

Xu, Weijian; Du, Zi‐Yi; Zhang, Wei‐Xiong

doi:10.1039/c6ce01485b

Cited by 149 publications

(117 citation statements)

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“…The presented materials belong to the so-called molecular perovskites [28] with a general formula of ABX 3 , which topologically mimic the cubic structure of the very well-known inorganic perovskites, the simplest high-symmetry structure for ternary compounds, but have at least one organic molecular component (usually A component). Recently, molecular perovskites have attracted growing attention, as illustrated by the extensive studies on methyl-ammonium lead iodide for high performance solar cells [29][30][31][32], and the phase transitions together with the relevant switching physical properties [33][34][35]. In the course of our investigation on relevant molecular perovskites [36], we discovered that, the well-known, low-cost oxidative perchlorate anion as X component, and compatible fuel organic cation as A component, can be easily assembled into molecular perovskites by one-pot reaction.…”

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confidence: 99%

Molecular perovskite high-energetic materials

et al. 2018

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Since the black powder, the first known explosive, was discovered by ancient Chinese in the seventh century, people have been finding powerful, stable, reliable and low-cost energetic materials for military equipment and civil industry. To obtain a better explosive performance, an efficient strategy is to load unstable chemical bonds [1][2][3], as well as to combine fuel with oxidizer components in a proper ratio for achieving sufficient combustion and rapid detonation [4][5][6]. An effective way is to incorporate fuel and oxidizer properties into a single molecule [7], as demonstrated by a series of classical organic nitro group/nitrogen-rich molecules, such as trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX), cyclotetramethylene tetranitramine (HMX), hexanitrohexaazaisowurtzitane (CL-20) and octanitrocubane (ONC) (Fig. S1). Loading more nitro groups and higher structural tension into a single molecule does improve explosive performance, but usually leads to complicated and not cost-effective synthetic procedures. By a trade-off of detonation performance and cost, HMX is regarded as the best military high-energetic explosives nowadays [7], although it is neither the most powerful one nor the cheapest one.Parallel to the intensive studies on molecule engineering on the backbone of nitrogen-rich organic energetic molecules [8,9], the exploration of advanced energetic materials extends to the crystal engineering on their energetic co-crystals [10-13], energetic salts [14][15][16][17][18][19][20], as well as coordination polymers or metal-organic frameworks [21][22][23][24][25][26][27]. The essential strategy is to control the intermolecular packing/linkage of the energetic organic fuel and oxidizer components in crystals by non-covalent interactions to modify/enhance the explosive performance and/or to reduce the sensitivity to a practicable level. However, for a specific energetic molecular component, it is highly challenging to predict/engineer the crystal structure of its co-crystals, salts, or metal-organic frameworks [10], and the examples with good detonation performance, high stability and low cost are still scarce.Here we present a promising solution, i.e., assembly of both low-cost organic fuel and oxidizer components into a closely packed, high-symmetry ternary compounds (vide infra), to achieve advanced energetic materials with a nice combination of high explosive power, high stability, and low cost. The presented materials belong to the so-called molecular perovskites [28] with a general formula of ABX 3 , which topologically mimic the cubic structure of the very well-known inorganic perovskites, the simplest high-symmetry structure for ternary compounds, but have at least one organic molecular component (usually A component). Recently, molecular perovskites have attracted growing attention, as illustrated by the extensive studies on methyl-ammonium lead iodide for high performance solar cells [29][30][31][32], and the phase transitions together with the ...

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Molecular perovskite high-energetic materials

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“…[164] Thus, from a design standpoint, such structures are much more flexible, leading to a vast increase of complexity but also potentially offering favorable properties once all materials design tuning knobs are understood and controllable. Note, however, that the shift from spherical (inorganic) ions to organic molecules is accompanied by a new sense of (bonding) direction.…”

Section: Organic X-site: Hp(x)mentioning

confidence: 99%

“…[81,164,175] HP(AX) structures employ many of the ligands we discussed for HP(A) and HP(X) compounds. [81,164,175] HP(AX) structures employ many of the ligands we discussed for HP(A) and HP(X) compounds.…”

Section: Organic A-and X-sites: Hp(ax)mentioning

confidence: 99%

Mix and Match: Organic and Inorganic Ions in the Perovskite Lattice

Gebhardt

Rappe

2018

Advanced Materials

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X-site anions are possible, with only two general requirements that must be fulfilled: i) charge neutrality in the ABX 3 unit (typically, X is a divalent or monovalent anion, hence A and B cations with oxidation states between +1 and +5 can be combined) and ii) the ionic radii of the chosen composition must allow the above coordination, or different phases become more stable. Both of these simple design rules have a certain flexibility.The electronic argument i) can be stretched by allowing the combination of multiple ABX 3 units to form an overall charge neutral unit. For example, this is the case when considering A 2 BB′X 6 or AA′B 2 X 6 systems. Such double perovskite systems are known with B and B′ (A and A′) being the same elemental species (disproportion in oxidation state, e.g., Cs 2 Au + Au 3+ I 6 ) [20] or different ones (e.g., SrBaTi 2 O 6 [21] and SrPbTi 2 O 6 [22] for A-site disproportion or K 2 NbTaO 6 [23] and Bi 2 FeCrO 6 [24] for the B-site). Of course, this concept can also be used to combine three ABX 3 units (e.g., (CaTiO 3 ) n (SrTiO 3 ) l (BaTiO 3 ) m [25-27]) and much more complex stoichiometries with mixed ratios (e.g., (Pb 2 InNbO 6 ) 3/4 (Ba 2 InBiO 6 ) 1/4 [28] or [CaMn 3 3+ ][Mn 3 3+ Mn 4+ ] O 12 ] [29] ). Furthermore, although the bonding character in oxide perovskites is often mainly ionic, some compositions have an increased level of covalency (e.g., halides, sulfides, Bi-and Pbbased oxide perovskites). Thus, the electronic shell configuration and other effects like the steric demands of a metal lonepair will influence the structure and stability of ABX 3 perovskite compounds.In addition, the geometric argument ii) allows for some flexibility. For a perfectly cubic perovskite, the (effective) ionic radii r must fulfill the relation of Goldschmidt's tolerance factor 2( ) 1 A X B X t r r r r = + + = . [30,31] However, perovskites can exist also with t being not ideal, usually in a range of about 0.75 < t < 1.05. [8] Whenever t ≠ 1, the crystal distorts from an ideal cubic lattice, usually in form of off-center displacements, octahedral rotations, or a combination of both. The classification of Glazer [32,33] can be used to describe such distortions from a perfectly cubic perovskite. [34] It is further possible that ABX 3 compounds are stable whose t does not fall into the interval that is required for the perovskite crystal structure. In these cases that are no longer stabilized by deformations and tilting, one observes other phases where the connectivity of BX 6Materials science evolves to a state where the composition and structure of a crystal can be controlled almost at will. Given that a composition meets basic requirements of stoichiometry, steric demands, and charge neutrality, researchers are now able to investigate a wide range of compounds theoretically and, under various experimental conditions, select the constituting fragments of a crystal. One intriguing playground for such materials design is the perovskite structure. While a game of mixing and matching ions has been pla...

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“…Now, ac omplex structural phase transition has been explored in aH OIP,[ CH 3 NH 3 ][Mn(N 3 ) 3 ], based on structural characterizations and ab initio lattice dynamics calculations.T his unusual first-order phase transition between two ordered phases at about 265 Ki sp rimarily driven by changes in the collective atomic vibrations of the whole lattice,a long with concurrent molecular displacements and an unusual octahedral tilting. Now, ac omplex structural phase transition has been explored in aH OIP,[ CH 3 NH 3 ][Mn(N 3 ) 3 ], based on structural characterizations and ab initio lattice dynamics calculations.T his unusual first-order phase transition between two ordered phases at about 265 Ki sp rimarily driven by changes in the collective atomic vibrations of the whole lattice,a long with concurrent molecular displacements and an unusual octahedral tilting.…”

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