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Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.

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The effect of radiation-induced disordering in a nuclear reactor (fast neutrons fluence Φ = 5 · 10 19 cm 2 , Tirr = 340 K) on resistivity ρ, superconducting transition temperature TC and upper critical field HC 2 of polycrystalline MgCNi3 samples was investigated. It was found that TC decreases under irradiation from 6.5 to 2.9 K and completely recovers after annealing at 600 • C. Temperature dependences ρ(T ) are characteristic of compounds with strong electron-phonon interaction. The dHC 2 /dT behaviour testifies to a considerable decrease in density of electronic state at Fermi level N (EF ) in the course of disordering.Radiation-induced disordering caused by irradiation with high-energy particles is a unique method of investigating the properties of superconducting and normal states of ordered crystals [1,2]. Even in broad-band metals, such as intermetallic compounds with A15 structure, long-range ordering loss leads to considerable rearrangement of the electronic spectrum, resulting in disappearance of individual features of the electronic structure. Disordering causes decrease in densities at Fermi level N (E F ) and respective noticeable drop of T C in compounds with high initial N (E F ) (Nb 3 Sn or V 3 Si), and considerable (from 1.5 to 7 K) rise of T C in compounds with low N (E F ) and T C due to growth of N (E F ) (Mo 3 Si and Mo 3 Ge) [3,4,5]. In type HTSC compounds, disordering leads to more significant changes in properties: fast and complete T C degradation is accompanied with N (E F ) decrease and metal-insulator transition [2]. Thus investigation of response of a system to radiation-induced disordering serves as a kind of a test to reveal the characteristic features of its electron states. It was shown in recent papers [6,7] that T C drop from 38 to 5 K observed at MgB 2 under radiation-induced disordering is connected mainly with considerable drop of N (E F ), similar to Nb 3 Sn or V 3 Si compounds. In our investigation, we concentrated on the effect of disordering on the properties of superconducting compound MgCNi 3 (T C ∼ 8 K) with perovskite cubic structure of type SrTiO 3 , unconventional for intermetallides [8]. Our interest in this system was explained by the fact that its ground state is close to ferromagnetic due to the presence of a narrow peak in N (E) located 45 meV below the Fermi level [9]. This allowed us to regard it as a candidate for an unconventional (possibly triplet) superconductivity, similar to Sr 2 RuO 4 compound. It is known that in Sr 2 RuO 4 , as distinct from conventional superconducting compounds (intermetallides), T C undergoes anomalously strong suppression even under a slight disorder [10]. In MgCNi 3 , maximum T C is achieved at excess of carbon content only (nominal composition MgC 1.5 Ni 3 ), even though, according to neutron diffraction study, the actual composition is closer to Mg 0.96 CNi 3 , and excess carbon occupies the region between sample grain boundaries [11].In the sample preparation, fine powders Mg, C and Ni with purity better than 99.5% were used...

Nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rate T,' of "B have been measured in superconducting polycrystalline Mg13 2 with T°"s = 39.5 K. It is shown that (T,T) -' and the Knight shift K, are independent of temperature and nearly isotropic above 1. Both of these quantities are decreased gradually in going to the superconducting state. According to NMR data the density of states near the Fermi level is flat at the scale of about 500 K. Some conclusions on the orbital content of the density of states at the Fermi level were drawn and compared with the results of the band structure calculations.

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