New Layered Perovskite Compounds, Srn+1Vn03n+l (n=1,2,3 and (0)
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New layered perovskite compounds, Sr=+lV=OS=+l (n=l, 2 and 3) and SrVOs(n=oo ) , were synthesized and the physical properties of the compounds with n=l, 2 and 00 were investigated. Sr2V0 4 was semi conductive and antiferromagnetic, but a weak ferromagnetic contribution to the susceptibility was observed below 45 K. However, SrSV20 7 exhibited a metallic electrical conduction and a Pauli-paramagnetism. SrLaV0 4 was also successfully synthesized and was found to be semiconductive. The crystal structures and electrical and magnetic properties of Sr=+lV=OS=+l (n=l, 2, 3 and 00 ) and SrLaV04 were com pared.Keywords:
Pauli exclusion principle
Electrical conduction
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We synthesized new layered iron arsenide oxides (Fe2As2)(Sr4(Sc,Ti)3O8), (Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5). The crystal structures of these compounds are tetragonal with a space group of I4/mmm. The structure of (Fe2As2)(Sr4(Sc,Ti)3O8) and (Fe2As2)(Ba4Sc3O7.5) consists of the alternate stacking of antifluorite Fe2As2 layers and triple perovskite-type oxide layers. The interlayer distance between the Fe planes of (Fe2As2)(Ba4Sc3O7.5) is ∼18.7 Å. Moreover, the a-axis of (Fe2As2)(Ba3Sc2O5) is the longest among the layered iron pnictides, indicating the structural flexibility of the layered iron pnictide containing perovskite-type layers. The bulk sample of (Fe2As2)(Sr4(Sc0.6Ti0.4)3O8) exhibited diamagnetism up to 28 K in susceptibility measurements.
Arsenide
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Abstract In order to shed light upon the nature and mechanism of 4f‐3d magnetic exchange interactions, a series of binuclear complexes of lanthanide(3+) and chromium(3+) with the general formula [Ln(L) 5 (H 2 O) 2 Cr(CN) 6 ]· m L· n H 2 O (Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ); x =5, y =2, m =1 or 2, n =2 or 2.5; L=2‐pyrrolidinone) and [Ln(L) 4 (H 2 O) 3 Cr(CN) 6 ] · n H 2 O (Ln=Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Er ( 10 ); x =4, y =3, m =0, n =1.5 or 2.0; L2‐pyrrolidinone) were prepared and the X‐ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln‐CN‐Cr unit, in which Ln 3+ in a square antiprism environment is bridged to an octahedral coordinated Cr 3+ ion through a cyano group. The magnetic properties of the complexes 3 and 6 – 10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g =1.98, J =0.40 cm −1 , zJ′ =−0.21 cm −1 on the basis of a binuclear spin system ( S Gd =7/2, S Cr =3/2), revealing an intra‐molecular Gd 3+ ‐Cr 3+ ferromagnetic interaction and an inter‐molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory (DFT), combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm −1 , supporting the observation of weak ferromagnetic intra‐molecular interaction in 7 . The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd 3+ and Cr 3+ was discussed.
Square antiprism
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Perovskite oxynitrides via cooperative cation insertion and O/N exchange in layered oxide, for potential pigments and photocatalysts.
Tetragonal crystal system
Cubic crystal system
Isostructural
Rietveld Refinement
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Isostructural
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Substitution (logic)
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Orthorhombic crystal system
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Abstract For Abstract see ChemInform Abstract in Full Text.
Characterization
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Characterization
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Isolated [BN3]6− ions embedded in an oxonitridosilicate framework structure were observed in the series Ba4Ln7[Si12N23O][BN3] with Ln=Pr, Nd, Sm. Presumably the [BN3]6− ions act as high-temperature stable templates which cause the formation of hexagonal cages in the [Si12N23O] framework structure (see picture). The isotypic title compounds Ba4Pr7[Si12N23O][BN3], Ba4Nd7[Si12N23O][BN3], and Ba4Sm7[Si12N23O][BN3] were prepared by reaction of Pr, Nd, or Sm, with barium, BaCO3, Si(NH)2, and poly(boron amide imide) in nitrogen atmosphere in tungsten crucibles using a radiofrequency furnace at temperatures up to 1650 °C. They were obtained as main products (≈70 %) embedded in a very hard glass matrix in the form of intense dark green (Pr), orange-brown (Sm), or dark red (Nd) large single crystals, respectively. The stoichiometric composition of Ba4Sm7[Si12N23O][BN3] was verified by a quantitative elemental analysis. According to the single-crystal X-ray structure determinations (Ba4Ln7[Si12N23O][BN3], Z=1, P with Ln=Pr: a=1225.7(1), c=544.83(9) pm, R1=0.013, wR2=0.030; Ln=Nd: a=1222.6(1), c=544.6(1) pm, R1=0.017, wR2=0.039; Ln=Sm: a=1215.97(5), c=542.80(5) pm, R1=0.047, wR2=0.099) all three compounds are built up by a framework structure [Si12N23O]23− of corner-sharing SiX4 tetrahedrons (X=O, N). The oxygen atoms are randomly distributed over the X positions. The trigonal-planar orthonitridoborate ions [BN3]6− and also the Ln(3)3+ are situated in hexagonal cages of the framework (bond lengths Si−(N/O) 169–179 pm for Ln=Pr). The remaining Ba2+ and Ln3+ ions are positioned in channels of the large-pored network. The trigonal-planar [BN3]6− ions have a B−N distance of 147.1(6) pm (for Ln=Pr). Temperature-dependent susceptibility measurements for Ba4Nd7[Si12N23O][BN3] revealed Curie–Weiss behavior above 60 K with an experimental magnetic moment of μexp=3.36(5) μB/Nd. The deviation from Curie–Weiss behavior below 60 K may be attributed to crystal field splitting of the J=9/2 ground state of the Nd3+ ions. No magnetic ordering is evident down to 4.2 K. Die Umsetzung der Lanthanoide Pr, Nd bzw. Sm mit Barium-Metall, BaCO3, Si(NH)2 sowie Poly(boramidimid) in Tiegeln aus Wolfram bei Temperaturen bis 1650 °C im Hochfrequenzofen unter Stickstoff-Atmosphäre führte zur Synthese der drei isotypen Verbindungen Ba4Ln7[Si12N23O][BN3] mit Ln=Pr, Nd bzw. Sm. Die Verbindungen wurden als Hauptprodukte (≈ 70 %) eingebettet in außerordentlich harten glasartigen Phasen in Form großer dunkelgrüner (Pr), orange-brauner (Sm) bzw. dunkelroter (Nd) Einkristalle erhalten. Die Zusammensetzung von Ba4Sm7[Si12N23O][BN3] wurde durch quantitative Elementaranalyse bestätigt. Nach Einkristall-Röntgenstrukturanalysen (Ba4Ln7[Si12N23O][BN3], Z=1, P mit Ln=Pr: a=1225.7(1), c=544.83(9) pm, R1=0.013, wR2=0.030; Ln=Nd: a=1222.6(1), c=544.6(1) pm, R1=0.017, wR2=0.039; Ln=Sm: a=1215.97(5), c=542.80(5) pm, R1=0.047, wR2=0.099) liegt in allen drei Verbindungen eine Raumnetzstruktur eckenverknüpfter SiX4-Tetraeder [Si12N23O]23− vor (X=O, N), in der die Sauerstoffatome statistisch auf die X-Positionen verteilt sind. Die trigonal planaren Orthonitridoborat-Ionen [BN3]6− sowie die Ln(3)3+ sind in hexagonalen Käfigen dieses Gerüstes eingelagert (Bindungslängen Si-(N/O) 169–179 pm, für Ln=Pr). Die verbleibenden Ba2+- sowie Ln3+-Ionen finden sich in den restlichen Kanälen der Gerüststruktur. Die trigonal planaren [BN3]6−-Ionen haben B-N-Bindungslängen von 147.1(6) pm (Wert für Ln=Pr). Temperaturabhängige Suszeptibilitätsmessungen an Ba4Nd7[Si12N23O][BN3] ergaben Curie-Weiss-Verhalten oberhalb von 60 K mit einem experimentell bestimmten magnetischen Moment von μexp=3.36(5) μB /Nd. Die Abweichung vom Curie-Weiss-Verhalten unterhalb von 60 K wird auf Kristallfeld-Aufspaltungen des J=9/2 Grundzustands der Nd3+-Ionen zurückgeführt. Bis 4.2 K konnte keine magnetische Ordnung nachgewiesen werden.
Stoichiometry
Barium
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Since the reports of CMR(colossal magnetoresistance) effects in some single crystal R-P phase , considerable researches have been carried out to find optimum composition and to understand the role of dimensionality in the CMR mechanism of these systems. In this study, layered perovskite (x=0.4, Ln=La, Pr, Nd, Sm, Eu, Gd) phases were synthesized by solid state reaction and their structures were refined by Rietveld method. Electrical and magnetic properties were measured between room temperature and liquid helium temperature and compared with those of phase. All samples prepared in air were identified as single phases and Jahn-Teller distortions were observed in all samples. Other lanthanide substituted R-P phases for lanthanium showed broad transition at around 70K from paramagnetic to weekly ferromagnetic phase.
Rietveld Refinement
Colossal Magnetoresistance
Single phase
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