Showing papers on "Perovskite (structure) published in 1970"
TL;DR: In this article, the authors present a review of the constitution of the mantle between depths of 200 and 1200 km in the light of recent high pressure experimental investigations on silicates and on their germanate analogues, concluding that the rapid increase of seismic velocity around 350-450 km is caused mainly by the transformation of olivine into a spinel-like structure and by transformation of pyroxenes into a new kind of garnet structure characterized by octahedral coordination of a substantial proportion of silicon atoms.
322 citations
TL;DR: In this article, a single crystal of Pb(Zn 1/3 Nb 2/3 )O 3 was investigated in the ferroelectric and paraelectric temperature regions.
Abstract: The ferroelectric properties of a single crystal of Pb(Zn 1/3 Nb 2/3 )O 3 were investigated in the ferroelectric and paraelectric temperature regions The crystal undergoes a ferroelectric phase transition in a wide temperature range, changing from cubic perovskite structure to rhombohedral one A broad peak was observed in the dielectric constant vs temperature curve, being characteristic of the disordered perovskite ferroelectrics The spontaneous polarizations were obtained from the hysteresis loop and the pyroelectric current, and there was found a discrepancy in both measurements Without applying an electric field the optical anisotropy was not detected But with the field the domain and the birefringence were observed The effects of the dc field on the dielectric constant and the birefringence were observed over the wide temperature range A brief explanation of the character of the phase transition as well as dielectric and optical properties were given
167 citations
88 citations
TL;DR: In this article, a new high-pressure form of Rh2O3 has been prepared at 65 k bar and 1200°C, and four-probe resistivity measurements made on a single crystal show that it is a semiconductor with a room-temperature resistivity of 130 Ω cm and an activation energy of 0.16 eV.
77 citations
TL;DR: In this article, a perovskite CaFeO 3 with a o = 3.770 A has been synthesized at high temperature and pressure and an isomer shift corresponding to the tetravalent state of iron and a Neel temperature of 120°K were obtained from Mossbauer spectra and magnetic susceptibility measurements.
74 citations
TL;DR: In this paper, preliminary results for Ca2Nb2O7 indicate a new type of structure for an A2B 2O7 compound containing BO6 octahedra.
Abstract: Preliminary results for Ca2Nb2O7 indicate a new type of structure for an A2B2O7 compound containing BO6 octahedra. This structure, which is distinct from the pyrochlore and weberite types, contains parallel slabs each having a distorted perovskite configuration, but arranged with a notable lack of Nb–O–Nb links between successive slabs. A comparison is made with the structures of NaNbO2F2 and certain ferroelectric ABF4 compounds. The absence of ferroelectricity in Ca2Nb2O7 is discussed.
57 citations
42 citations
Journal Article•
TL;DR: In this paper, the authors used an ARL electronprobe using mineral standards ani computer techniques which by now must be standard for all the analysis of all the analyzed minerals.
Abstract: The rocks in which the analyzed minerals occur are' with one exception, all lavas and may be divided into three groups' These are (Table 1): a) Lavas which contain microphenocrysts of sphene' bj Lurrur, except for a monticellite peridotite, which contain micro' phenocrysts of perovskite. Perovskite is found with various combinations of augite, olivine, phlogopite, melilite, nepheline' kalsil i te and leucite (Table 1). c) Lavas which contain both sphene and perovskite' These are etindites (Tilley, 1953) which contain titanaugite zoned towards acmite' iitu.to*ugn\"tite, nepheline, interstitial leucite and early crystallization perovskite with sphene in the groundmass' All the mineral analyses were made with an ARL electronprobe using mineral standards ani computer techniques which by now must be standard.
37 citations
TL;DR: The oxygen-deficient pyrochlore Pb 2 Ru 2 O 7−x transforms to an orthorhombic perovskite near 90 kbar and 1400° C as discussed by the authors.
26 citations
TL;DR: A number of newly synthesized compounds of the type Pb3B2WO9 and Pb2BWO6 with the perovskite structure are reported where B is Cr, Co, Sc, In, Ni, Mn, Fe or Zn as mentioned in this paper.
18 citations
TL;DR: In this paper, the structure of the perovskite compound Sr NiIITeVI(6)O6 (1:1 order in the octahedral sites) is described in detail.
Abstract: Auf Grund von Einkristalldaten wird die Struktur des auf den Oktaederplatzen geordneten Perowskits Sr[NiIITeVI](6)O6 beschrieben (wahrscheinliche Raumgruppe: C). Der erhaltene NiO-Abstand (2,04 A aTe–O = 1,91 A) in dieser Verbindung zusammen mit dem im entsprechenden Wolframperowskit (II. Mitteilung) soll eine quantitative Analyse des Zusammenhangs von Struktur und Ligandenfeld- sowie Elektronenresonanzdaten ermoglichen. Schon der Vergleich dieses Abstands und der spektroskopischen Daten des Tellurperowskits mit entsprechenden Werten von NiII-haltigem MgO zeigt jedoch, das eine Interpretation auf der Grundlage eines ionogenen Modells inadaquat ist.
The structure of the perovskite compound Sr NiIITeVI(6)O6 (1:1 order in the octahedral sites) is described in detail. The obtained NiO distance (2.04 A aTe–O = 1.91 A) together with that one within the corresponding tungsten perovskite (part II) will be analyzed quantitatively with respect to the connection between structure and ligand-field as well as EPR data. The comparison of this distance and the spectroscopic results of the tellurium perovskite with corresponding data of NiII-doped MgO however shows already now that an interpretation on the basis of an ionic model is impossible
TL;DR: The compounds TlMnCl3, TlFeCl3 and TlNiCl3 were prepared by heating T1C1 with the corresponding transition metal dichloride in an evacuated ampoule as mentioned in this paper.
Abstract: The compounds TlMnCl3, TlFeCl3, TlCoCl3 and TlNiCl3 were prepared by heating T1C1 with the corresponding transition metal dichloride in an evacuated ampoule. Atomic positions were determined from powder photographs. All four compounds were found to be related to the perovskite type structure. TlMnCl3 has a cubic structure, space group Pm3m, with ao = 5.025 A. The other three compounds are hexagonal, probable space group P63mc, with cell dimensions (in A) a0 = 6.976 and c0 = 6.008 for the Fe compound, a0 = 6.907 and c0 = 5.981 for the Co compound and a0 = 6.863 and c0 = 5.881 for the Ni compound. The three hexagonal compounds are isomorphous. A measureable concentration of basal plane stacking faults was found to occur in TlFeCl3 and also, to a lesser degree, in TlCoCl3.
TL;DR: In this article, theoretical Madelung lattice energies are calculated for several oxides (FeO, Al 2 O 3, Cr 2O 3, Fe 2 O 2, SiO 2, TiO 2 ), spinels (Al 2 MgO 4, MgSiO 3 ), and perovskites (CaTiO 3, SrTiO3, Mg SiO 3), Fe 2 3+ O 3, Fe 2+ Fe 4+ O 4, Fe 3 O 4 ) to determine the admissibility of these proposed structures.
TL;DR: In this article, phase relationships in the system CaONb 2 O 5 TiO 2 have been studied and a Griffin-Telin hot-stage microscope was used for the determination of the liquidus temperatures, because the mixture of compositions in this system did not form glasses, thus rendering the quench technique inapplicable.
Abstract: Phase relationships in the system CaONb 2 O 5 TiO 2 have been studied. A Griffin-Telin hot-stage microscope was used for the determination of the liquidus temperatures, because the mixtures of compositions in this system did not form glasses, thus rendering the quench technique inapplicable. The liquidus fields of the following ternary compounds have been outlined, in addition to those of the binary compounds: (a) a compound having the composition 3CaO.Nb 2 O 5 .3TiO 2 , a pyrochlore structure and melting incongruently; its composition has been determined by subsolidus experiments; (b) a compound having a composition 8CaO.7Nb 2 O 5 .6TiO 2 that melted congruently and appeared to be metastable at subsolidus temperatures; its presence has been established from the shape of the liquidus surface; and (c), another ternary compound, having a composition 6CaO.Nb 2 O 5 .3TiO 2 and melting congruently; its existence has also been established from the shape of the liquidus surface. Perovskite (CaO.TiO 2 ) did not form solid solutions with any of the calcium niobates notwithstanding that the compound 4CaO.Nb 2 O 5 and probably those niobates having a still higher lime content, have a perovskite type of structure.
TL;DR: In this paper, Raman scattering of 5145 −A argon laser radiation by two magnons in the perovskite antiferromagnet KNiF3 has been observed.
Abstract: Raman scattering of 5145‐A argon laser radiation by two magnons in the perovskite antiferromagnet KNiF3 has been observed. At low temperature, the spectrum of the scattered light is in excellent agreement with a Green's function theory for a perovskite with S = 1 and nearest‐neighbor exchange constant J = (71.0±0.8) cm−1. If the effects of anisotropy (obtained from far‐infrared antiferromagnetic resonance measurements) are included, the value of J is changed only slightly, decreasing ≈0.5 cm−1. The line shape and position were also observed as functions of temperature. A comparison is made with similar scattering observed in RbMnF3 (S=52) and in related magnetic Ni2+ fluorides.
TL;DR: In this article, a serie of lacunary ordered perovskites including tetravalent uranium of A2II BII UIV O5 type has been prepared by solid state reaction.
TL;DR: By the solid state reaction of the mixture 3PbO+ZnO+Nb2O5 a pyrochlore-type (Pb, Zn)2Nb 2O7, was obtained, while perovskite-type A2+(B2+1/3Nb5+2/3)O3 (A2+=Ba, Sr and B2+=Zn, Mg, Co, Ni, Ni; A2+=Pb2+ and B 2+=Mg, Nb2+, Co,
Abstract: By the solid state reaction of the mixture 3PbO+ZnO+Nb2O5 a pyrochlore-type (Pb, Zn)2Nb2O7, was obtained, while perovskite-type A2+(B2+1/3Nb5+2/3)O3 (A2+=Ba, Sr and B2+=Zn, Mg, Co, Ni; A2+=Pb2+ and B2+=Mg, Co, Ni) can be prepared by usual solid state reactions. To obtain a perovskite-type Pb(Zn1/3Nb2/3)O3, a pressure higher than 25 kbars at 800°-1000°C was necessary. Another method to obtain the perovskite form was quenching the molten solution from the temperatures higher than 1200°C. These conditions are considered to favor Zn coordination number to change into 6.
01 Jan 1970
TL;DR: In this article, the two-time Green function was applied to the study of spin-wave impurity modes at low temperatures. But the results were not compared with two experiments on Ni 2+ and Eu 3+ impurities in KMnF 3.
TL;DR: In this article, the relative atomic displacements of the sublattices of perovskite strontium titanate associated with optical frequency mode are calculated using all possible interionic couplings.
Abstract: The relative atomic displacements of the sublattices of perovskite strontium titanate associated with optical frequency mode are calculated using all possible interionic couplings The couplings are estimated from the observed optical frequencies of SrTiO3 The results of the calculation are plotted as a function of a parameter Φ(∼T – Tc) It is found that two sets of solutions exist which correspond to the proposals of SLATER and LAST