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La0.7Ca0.3Mn0.5Fe0.5O3(LCMFO) ceramic samples were prepared by conventional solid-state reaction. X-Ray diffraction investigations show that samples have orthorhombic space group Pnma (a = 5.447(2) Ǻ, b = 7.709(3) Ǻ, c = 5.467(3) Ǻ). During the neutron powder diffraction measurements of LCMFO in the temperature range of 10 ÷ 300 K the antiferromagnetic long-range ordering of G-type was seen. It has been established that 50% substitution of Mn/Fe leads to a complete suppression of the ferromagnetism in LCMFO samples. Investigations of temperature dependence of the magnetization, M(T), suggests the frustration of magnetic ground state and the existence of a spin-glass or a cluster-glass phase below the magnetic transition temperature close to 350 K. The temperature dependences of conductivity for La0.7Ca0.3Mn0.5Fe0.5O3sample investigated in magnetic fields B = 0 and 1 T. According to the research, the mechanisms of hopping conductivity were established. Micro parameters in density of localized states were calculated for LCMFO samples. The width of the Coulomb gap Δ = 0.67 eV, rigid gap δ = 0.324 eV and the localization radii of charge carriers were estimated. [ABSTRACT FROM PUBLISHER]

The crystal and magnetic structures of hexagonal manganites YMnO3 and LuMnO3 have been studied by powder neutron diffraction up to 6 GPa in the temperature range of 10-300 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a Γ1 irreducible representation is stable below TN=70 K in YMnO3. Upon application of high pressure, a spin-reorientation was observed and the triangular AFM structure evolves from Γ1 to Γ1+Γ2 representation symmetry. In LuMnO3, the triangular AFM state of a Γ2 symmetry with TN ≈ 95 K remains stable in the investigated pressure range. The ordered Mn magnetic moment is suppressed at high pressure and low temperature, with much more pronounced effects for YMnO3, indicating enhanced spin fluctuations due to stronger magnetic frustration of the triangular lattice under higher pressure. The relationship between the evolution of spin fluctuations and in-plane Mn-O bonds under pressure is analyzed. [ABSTRACT FROM AUTHOR]

The magnetic and crystal structures of anion-deficient La0.7Sr0.3MnO3− d manganites ( d = 0.15 and 0.20) are studied by neutron diffraction in the range of high pressures 0–5 GPa and temperatures 10–300 K. It is found that a spin-glass state forms in La0.7Sr0.3MnO2.85 below T g ∼ 50 K, while magnetic phase separation is observed in La0.7Sr0.3MnO2.80, which is characterized by the coexistence of AFM domains of the C type with spin-glass domains. As distinct from the stoichiometric A0.5Ba0.5MnO3 manganites (A = Nd, Sm), in which the high-pressure effect suppresses the spin-glass state and gives rise to ferromagnetism, the spin-glass state in La0.7Sr0.3MnO2.85 is stable under pressure. The bulk modulus of La0.7Sr0.3MnO2.85 is considerably smaller than that for the stoichiometric La0.7Sr0.3MnO3 compound. The causes of the formation of different types of the magnetic structure in La0.7Sr0.3MnO3− d ( d = 0.15 and 0.20) and different high-pressure effects on the magnetic structure of stoichiometric and anion-deficient manganites are analyzed. [ABSTRACT FROM AUTHOR]

A crystal and magnetic structure of manganites Pr 0.7 Ca 0.3 Mn 1- y Fe y O 3 ( y  = 0, 0.1) has been studied by means of powder neutron diffraction at pressures up to 4 GPa in the temperature range 15-300 K. Under high pressure, an appearance of A-type antiferromagnetic state in both systems was observed. Both compounds exhibit anisotropic compression of the lattice which leads to the apical compression of MnO 6 octahedra along the crystallographic b -axis. The calculated from obtained structural data pressure dependence of the charge-carrier bandwidth is in a qualitative agreement with observed pressure behavior of insulator-metal transition temperature within the framework of the double-exchange model. [ABSTRACT FROM AUTHOR]

Vibrational spectra of NH[sub 4]I have been studied by means of incoherent inelastic neutron scattering at pressures up to 10 GPa using a high-pressure cell of the "toroid" type with tungsten carbide anvils. Librational (L) and transverse optical (TO) mode frequencies as a function of pressure were obtained. The observed behavior of these modes may be explained in terms of their hybridization at pressures P > 6 GPa. A change of dynamics of NH[sub 4]I due to this effect is a possible mechanism for the phase transition which occurs in this system at high pressure. [ABSTRACT FROM AUTHOR]

The structure of ternary mercury chalcogenides HgSe[sub 1-x]S[sub x] (x = 0.3, 0.5, 0.6) and HgTe[sub 1-x]S[sub x] (x = 0.15) was studied by means of powder neutron diffraction at pressures up to 8 GPa. A phase transition from the zinc blende cubic structure to the hexagonal cinnabar structure was observed at P ≈ 1 GPa in HgSe[sub 1-x]S[sub x] systems and at P ≈ 1.6 GPa in HgTe[sub 0.85]S[sub 0.15]. A coexistence of these two phases was observed in the vicinity to the transition pressure. Lattice parameters and atomic positional parameters for the high-pressure hexagonal phase were determined. [ABSTRACT FROM AUTHOR]

High-pressure neutron-diffraction experiments on the pseudo-ternary compound NdAl[sub x]Ga[sub 2-x] revealed a pressure-induced isostructural phase transition for x = 1.00 and 1.08 above about 1.5 GPa at room temperature. Within its hexagonal AlB[sub 2] structure the compound changes its lattice ratio c/a discontinuously from 0.97 to 0.84 in analogy to chemical pressure for x > 1.12. Pressures up to 5.2 GPa did not result in a pure high-pressure phase but rather in a mixture of both phases. The intermetallic MN[sub 2] phases of the AlB[sub 2] structure are known to appear in two distinct groups with different c/a ratios. The observed isostructural transition is discussed within the framework of near-neighbor diagrams. [ABSTRACT FROM AUTHOR]