53 research outputs found
Griffiths phase-like behaviour and spin-phonon coupling in double perovskite TbNiMnO
The Griffiths phase-like features and the spin-phonon coupling effects
observed in TbNiMnO are reported. The double perovskite compound
crystallizes in monoclinic space group and exhibits a magnetic phase
transition at 111 K as an abrupt change in magnetization. A negative
deviation from ideal Curie-Weiss law exhibited by 1/ curves and
less-than-unity susceptibility exponents from the power-law analysis of inverse
susceptibility are reminiscent of Griffiths phase-like features. Arrott plots
derived from magnetization isotherms support the inhomogeneous nature of
magnetism in this material. The observed effects originate from
antiferromagnetic interactions which arise from inherent disorder in the
system. Raman scattering experiments display no magnetic-order-induced phonon
renormalization below in TbNiMnO which is different from the
results observed in other double perovskites and is correlated to the smaller
size of the rare earth. The temperature evolution of full-width-at-half-maximum
for the {\it stretching} mode at 645 cm presents an anomaly which
coincides with the magnetic transition temperature and signals a close
connection between magnetism and lattice in this material.Comment: 17 pages, 8 figures; accepted in J. Appl. Phy
Effect of pressure on octahedral distortions in RCrO3 (R = Lu, Tb, Gd, Eu, Sm): The role of R-ion size and its implications
The effect of rare-earth ion size on the octahedral distortions in rare-earth
chromites (RCrO3, R = Lu, Tb, Gd, Eu, Sm) crystallizing in the orthorhombic
structure has been studied using Raman scattering and synchrotron powder x-ray
diffraction up to 20 GPa. From our studies on RCrO3 we found that the
octahedral tilts (distortions) increase with pressure. This is contrary to the
earlier report which suggests that in LaCrO3, the distortions decrease with
pressure leading to a more ordered phase at high pressure. Here we observe that
the rate of increase in distortion decreases with the increase in R-ion radii.
This occurs due to the reduction in the compression of RO12 polyhedra with a
corresponding increase in the compression of the CrO6 octahedra with increasing
R-ion radii. From the Raman studies, we predict a critical R-ion radii, above
which we expect the distortions in RCrO3 to reduce with increasing pressure
leading to what is observed in the case of LaCrO3. These Raman results are
consistent with our pressure dependent structural studies on RCrO3 (R = Gd, Eu,
Sm). Also, our results suggest that the pressure dependence of N\'eel
temperature, TNCr, (where the Cr3+ spin orders) in RCrO3 is mostly affected by
the compressions of Cr-O bonds rather than the alteration of octahedral tilts.Comment: 17 pages, 8 figures This manuscript has been published in Material
Research Expres
Rb2Cd3(SO4)(3)(OH)(2)center dot H2O: structural stability at 500 K
The title compound, dirubidium tricadmium tris(sulfate) dihydroxide dihydrate, consists of sheets of CdO6 octahedra and sulfate tetrahedra propagating in the (100) plane, with Rb+ ions in the interlayer positions. It is isostructural with K2Co3(SO4)(3)(OH)(2)(.)2H(2)O
(NH4)2Cd3(SO4)4·5H2O
The title compound, diammonium tricadmium tetrakis(sulfate) pentahydrate, (NH4)(2)Cd-3(SO4)(4)center dot 5H(2)O, was formed during an attempted synthesis of the langbeinite, (NH4)(2)Cd-2 (SO4)(3). The structure has two layers, one containing Cd octahedra bridged by sulfate groups and the other containing edge-shared Cd octahedra, with NH4 units occupying interstitial positions. The layers are connected by way of Cd-O-S links
Dirubidium tricadmium tetrakis(sulfate) pentahydrate
The title compound, , arose as an unexpected product during the attempted synthesis of an potassium cadmium sulfate langbeinite, It has two layers, layer A containing Cd octahedra bridged by sulfate groups and layer B containing edge-shared Cd octahedra, with Rb atoms occupying interstial positions. The layers are connected by way of Cd-O-S links
In Situ Phase Separation Following Dehydration in Bimetallic Sulfates: A Variable-Temperature X-Ray Diffraction Study
Phase separation resulting in a single-crystal-single-crystal transition accompanied by a polycrystalline phase following the dehydration of hydrated bimetallic sulfates [Na2Mn1.167(SO4)(2)S0.33O1.167 center dot 2H(2)O and K4Cd3-(SO4)(5)center dot 3H(2)O] has been investigated by in situ variable-temperature single-crystal X-ray diffraction. With two examples, we illustrate the possibility of generating structural frameworks following dehydration in bimetallic sulfates, which refer to the possible precursor phases at that temperature leading to the mineral formation. The room-temperature structure of Na2Mn1.167(SO4)(2)S0.33O1.167 center dot 2H(2)O is trigonal, space group R (3) over bar. On heating the crystal in situ on the diffractometer, the diffraction images display spherical spots and concentric rings suggesting phase separation, with the spherical spots getting indexed in a monoclinic space group, C2/c. The structure determination based on this data suggests the formation of Na2Mn(SO4)(2). However, the diffraction images from concentric rings could not be indexed. In the second example, the room-temperature structure is determined to be K4Cd3(SO4)(5)center dot 3H(2)O, crystallizing in a monoclinic space group, P2(1)/n. On heating the crystal in situ, the diffraction images collected also have both spherical spots and diffuse rings. The spherical spots could be indexed to a cubic crystal system, space group P2(1)3, and the structure is K4Cd3(SO4)(3). The possible mechanism for the phase transition in the dehydration regime resulting in this remarkable single-crystal to single-crystal transition with the appearance of a surrogate polycrystalline phase is proposed
In Situ Phase Separation Following Dehydration in Bimetallic Sulfates: A Variable-Temperature X-Ray Diffraction Study
Impact of organic amine cations on photoluminescence and magnetic properties in Dion-Jacobson hybrid manganese halide perovskites
A strenuous effort has been made to design multifunctional lead-free organic–inorganic hybrid (OIH) halide compounds, which are envisioned as next generation solar cell materials. However, it is challenging to design OIH halides that can exhibit both long-range magnetic ordering and high photoluminescence quantum yield (PLQY) since the dimensionality of the compounds has a contrasting effect on them. In this article, we have shown an approach to enhance PLQY in two-dimensional (2D) Heisenberg antiferromagnets by increasing the alkylene chain length of [H3N–(CH2)m–NH3]MnCl4 (m = 2, 3, and 4) compounds. All these compounds exhibit 2D layers of corner-sharing MnCl6 octahedra where the organic cations are intercalated between them. These compounds exhibit long-range antiferromagnetic ordering confirmed by the DC magnetic susceptibility and heat capacity measurements. The Néel temperature (TN) decreases with increasing the length of spacer cations due to a decrease in interlayer exchange interactions; however, interestingly, the lifetime of photoexcited electrons and PLQY enhances from 24 to 56 µs and 8% to 23%, respectively. Furthermore, the temperature-dependent photoluminescence measurements provide insight into thermal quenching and exciton binding energy. We believe this study can help to design new OIH halides with long-range magnetic ordering and high PLQY
Polymorphism and Phase Transformation Behavior of Solid Forms of 4-Amino-3,5-dinitrobenzamide
We report the preparation, analysis, and phase transformation behavior of polymorphs and the hydrate of 4-amino-3,5-dinitrobenzamide. The compound crystallizes in four different polymorphic forms, Form I (monoclinic, P2(1)/n), Form II (orthorhombic, Pbca), Form III (monoclinic, P2(1)/c), and Form IV (monoclinic, P2(1)/c). Interestingly, a hydrate (triclinic, P (1) over bar) of the compound is also discovered during the systematic identification of the polymorphs. Analysis of the polymorphs has been investigated using hot stage microscopy, differential scanning calorimetry, in situ variable-temperature powder X-ray diffraction, and single-crystal X-ray diffraction. On heating, all of the solid forms convert into Form I irreversibly, and on further heating, melting is observed. In situ single-crystal X-ray diffraction studies revealed that Form II transforms to Form I above 175 degrees C via single-crystal-to-single-crystal transformation. The hydrate, on heating, undergoes a double phase transition, first to Form III upon losing water in a single-crystal-to-single-crystal fashion and then to a more stable polymorph Form I on further heating. Thermal analysis leads to the conclusion that Form II appears to be the most stable phase at ambient conditions, whereas Form I is more stable at higher temperature
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