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Determining the structure-to-property relationship of materials becomes particularly challenging when the material under investigation is dominated by defects and structural disorder. Knowledge on the exact atomic arrangement at the defective structure is required to understand its influence on the functional properties. However, standard diffraction techniques deliver structural information that is averaged over many unit cells. In particular, information about defects and order-disorder phenomena is contained in the coherent diffuse scattering intensity which often is difficult to uniquely interpret. Thus, the examination of the local disorder in materials requires a direct method to study their structure on the atomic level with chemical sensitivity. Using aberration-corrected scanning transmission electron microscopy in combination with atomic-resolution electron energy-loss spectroscopy, we show that the controversial structural arrangement of the Fe2O2+δ layers in the mixed ionic-electronic conducting Sr4Fe6O12+δ perovskite can be unambiguously resolved. Our results provide direct experimental evidence for the presence of a nanomixture of "ordered" and "disordered" domains in an epitaxial Sr4Fe6O12+δ thin film. The most favorable arrangement is the disordered structure and is interpreted as a randomly occurring but well-defined local shift of the Fe-O chains in the Fe2O2+δ layers. By analyzing the electron energy-loss near-edge structure of the different building blocks in the Sr4Fe6O12+δ unit cell we find that the mobile holes in this mixed ionic-electronic conducting oxide are highly localized in the Fe2O2+δ layers, which are responsible for the oxide-ion conductivity. A possible link between disorder and oxygen-ion transport along the Fe2O2+δ layers is proposed by arguing that the disorder can effectively break the oxygen diffusion pathways.

Cs7Nd11(SeO3)12Cl16, the complex selenite chloride of cesium and neodymium, was synthesized in the NdOCl-SeO2-CsCl system. The compound has been characterized using single-crystal X-ray diffraction, electron diffraction, transmission electron microscopy, luminescence spectroscopy, and second-harmonic-generation techniques. Cs7Nd11(SeO3)12Cl16 crystallizes in an orthorhombic unit cell with a = 15.911(1) Å, b = 15.951(1) Å, and c = 25.860(1) Å and a noncentrosymmetric space group Pna2(1) (No. 33). The crystal structure of Cs7Nd11(SeO3)12Cl16 can be represented as a stacking of Nd11(SeO3)12 lamellas and CsCl-like layers. Because of the layered nature of the Cs7Nd11(SeO3)12Cl16 structure, it features numerous planar defects originating from occasionally missing the CsCl-like layer and violating the perfect stacking of the Nd11(SeO3)12 lamellas. Cs7Nd11(SeO3)12Cl16 represents the first example of a noncentrosymmetric structure among alkaline-metal lanthanide selenite halides. Cs7Nd11(SeO3)12Cl16 demonstrates luminescence emission in the near-IR region with reduced efficiency due to a high concentration of Nd(3+) ions causing nonradiative cross-relaxation.

The Li-ion rechargeable battery, due to its high energy density, has driven remarkable advances in portable electronics. Moving toward more sustainable electrodes could make this technology even more attractive to large-volume applications. We present here a new family of 3d-metal hydroxysulfates of general formula LiMSO4OH (M = Fe, Co, and Mn) among which (i) LiFeSO4OH reversibly releases 0.7 Li(+) at an average potential of 3.6 V vs Li(+)/Li(0), slightly higher than the potential of currently lauded LiFePO4 (3.45 V) electrode material, and (ii) LiCoSO4OH shows a redox activity at 4.7 V vs Li(+)/Li(0). Besides, these compounds can be easily made at temperatures near 200 °C via a synthesis process that enlists a new intermediate phase of composition M3(SO4)2(OH)2 (M = Fe, Co, Mn, and Ni), related to the mineral caminite. Structurally, we found that LiFeSO4OH is a layered phase unlike the previously reported 3.2 V tavorite LiFeSO4OH. This work should provide an impetus to experimentalists for designing better electrolytes to fully tap the capacity of high-voltage Co-based hydroxysulfates, and to theorists for providing a means to predict the electrochemical redox activity of two polymorphs.

A first clathrate compound with selenium guest atoms, [Ge(46-x)P(x)]Se(8-y)□(y) (x = 15.4(1); y = 0-2.65; □ denotes a vacancy), was synthesized as a single-phase and structurally characterized. It crystallizes in the space group Fm3 with the unit cell parameter a varying from 20.310(2) to 20.406(2) Å and corresponding to a 2 × 2 × 2 supercell of a usual clathrate-I structure. The superstructure is formed due to the symmetrical arrangement of the three-bonded framework atoms appearing as a result of the framework transformation of the parent clathrate-I structure. Selenium guest atoms occupy two types of polyhedral cages inside the positively charged framework; all selenium atoms in the larger cages form a single covalent bond with the framework atoms, relating the title compounds to a scanty family of semiclathrates. According to the measurements of electrical resistivity and Seebeck coefficient, [Ge(46-x)P(x)]Se(8-y)□(y) is an n-type semiconductor with E(g) = 0.41 eV for x = 15.4(1) and y = 0; it demonstrates the maximal thermoelectric power factor of 2.3 × 10(-5) W K(-2) m(-1) at 660 K.

La(3.2)Ba(0.8)Mn(3)O(10), a representative of the rare n = 3 members of the Ruddlesden-Popper manganites A(n+1)Mn(n)O(3n+1), was synthesized in an evacuated sealed silica tube. Its crystal structure was refined from a combination of powder X-ray diffraction (PXD) and precession electron diffraction (PED) data, with the rotations of the MnO(6) octahedra described within the symmetry-adapted mode approach (space group Cccm, a = 29.068(1) Å, b = 5.5504(5) Å, c = 5.5412(5) Å; PXD R(F) = 0.053, R(P) = 0.026; PED R(F) = 0.248). The perovskite block in La(3.2)Ba(0.8)Mn(3)O(10) features an octahedral tilting distortion with out-of-phase rotations of the MnO(6) octahedra according to the (Φ,Φ,0)(Φ,Φ,0) mode, observed for the first time in the n = 3 Ruddlesden-Popper structures. The MnO(6) octahedra demonstrate a noticeable deformation with the elongation of two apical Mn-O bonds due to the Jahn-Teller effect in the Mn(3+) cations. The relationships between the octahedral tilting distortion, the ionic radii of the cations at the A- and B-positions, and the mismatch between the perovskite and rock-salt blocks of the Ruddlesden-Popper structure are discussed. At low temperatures, La(3.2)Ba(0.8)Mn(3)O(10) reveals a sizable remnant magnetization of about 1.3 μ(B)/Mn at 2 K, and shows signatures of spin freezing below 150 K.

Three new ternary copper phosphides, Sr(2)Cu(6)P(5), Eu(2)Cu(6)P(5), and EuCu(4)P(3), have been synthesized from the elements in evacuated silica capsules. Eu(2)Cu(6)P(5) and Sr(2)Cu(6)P(5) adopt the Ca(2)Cu(6)P(5)-type structure, while EuCu(4)P(3) is isostructural to BaMg(4)Si(3) and still remains the only representative of this structure type among the ternary Cu pnictides. All three materials show metallic conductivity in the temperature range 2 K ≤ T ≤ 290 K, with no indication for superconductivity. For Eu(2)Cu(6)P(5) and EuCu(4)P(3), long-range magnetic order was observed, governed by 4f local moments on the Eu atoms with predominant ferromagnetic interactions. While Eu(2)Cu(6)P(5) shows a single ferromagnetic transition at T(C) = 34 K, the magnetic behavior of EuCu(4)P(3) is more complex, giving rise to three consecutive magnetic phase transitions at 70, 43, and 18 K.

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO(3) (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO(3) has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO(3)., (© 2012 American Chemical Society)

Three different perovskite-related phases were isolated in the SrGa(1-x)Sc(x)O(2.5) system: Sr(2)GaScO(5), Sr(10)Ga(6)Sc(4)O(25), and SrGa(0.75)Sc(0.25)O(2.5). Sr(2)GaScO(5) (x = 0.5) crystallizes in a brownmillerite-type structure [space group (S.G.) Icmm, a = 5.91048(5) Å, b = 15.1594(1) Å, and c = 5.70926(4) Å] with complete ordering of Sc(3+) and Ga(3+) over octahedral and tetrahedral positions, respectively. The crystal structure of Sr(10)Ga(6)Sc(4)O(25) (x = 0.4) was determined by the Monte Carlo method and refined using a combination of X-ray, neutron, and electron diffraction data [S.G. I4(1)/a, a = 17.517(1) Å, c = 32.830(3) Å]. It represents a novel type of ordering of the B cations and oxygen vacancies in perovskites. The crystal structure of Sr(10)Ga(6)Sc(4)O(25) can be described as a stacking of eight perovskite layers along the c axis ...[-(Sc/Ga)O(1.6)-SrO(0.8)-(Sc/Ga)O(1.8)-SrO(0.8)-](2).... Similar to Sr(2)GaScO(5), this structure features a complete ordering of the Sc(3+) and Ga(3+) cations over octahedral and tetrahedral positions, respectively, within each layer. A specific feature of the crystal structure of Sr(10)Ga(6)Sc(4)O(25) is that one-third of the tetrahedra have one vertex not connected with other Sc/Ga cations. Further partial replacement of Sc(3+) by Ga(3+) leads to the formation of the cubic perovskite phase SrGa(0.75)Sc(0.25)O(2.5) (x = 0.25) with a = 3.9817(4) Å. This compound incorporates water molecules in the structure forming SrGa(0.75)Sc(0.25)O(2.5)·xH(2)O hydrate, which exhibits a proton conductivity of ∼2.0 × 10(-6) S/cm at 673 K.

Since invention of the diamond anvil cell technique in the late 1950s for studying materials at extreme conditions, the maximum static pressure generated so far at room temperature was reported to be about 400 GPa. Here we show that use of micro-semi-balls made of nanodiamond as second-stage anvils in conventional diamond anvil cells drastically extends the achievable pressure range in static compression experiments to above 600 GPa. Micro-anvils (10-50 μm in diameter) of superhard nanodiamond (with a grain size below ∼50 nm) were synthesized in a large volume press using a newly developed technique. In our pilot experiments on rhenium and gold we have studied the equation of state of rhenium at pressures up to 640 GPa and demonstrated the feasibility and crucial necessity of the in situ ultra high-pressure measurements for accurate determination of material properties at extreme conditions.

The crystal structures of the three high-temperature polymorphs of K(3)AlF(6) have been solved from neutron powder diffraction, synchrotron X-ray powder diffraction, and electron diffraction data. The β-phase (stable between 132 and 153 °C) and γ-phase (stable between 153 to 306 °C) can be described as unusually complex superstructures of the double-perovskite structure (K(2)KAlF(6)) which result from noncooperative tilting of the AlF(6) octahedra. The β-phase is tetragonal, space group I4/m, with lattice parameters of a = 13.3862(5) Å and c = 8.5617(3) Å (at 143 °C) and Z = 10. In this phase, one-fifth of the AlF(6) octahedra are rotated about the c-axis by ∼45° while the other four-fifths remain untilted. The large ∼45° rotations result in edge sharing between these AlF(6) octahedra and the neighboring K-centered polyhedra, resulting in pentagonal bipyramidal coordination for four-fifths of the K(+) ions that reside on the B-sites of the perovskite structure. The remaining one-fifth of the K(+) ions on the B-sites retain octahedral coordination. The γ-phase is orthorhombic, space group Fddd, with lattice parameters of a = 36.1276(4) Å, b = 17.1133(2) Å, and c = 12.0562(1) Å (at 225 °C) and Z = 48. In the γ-phase, one-sixth of the AlF(6) octahedra are randomly rotated about one of two directions by ∼45° while the other five-sixths remain essentially untilted. These rotations result in two-thirds of the K(+) ions on the B-site obtaining 7-fold coordination while the other one-third remain in octahedral coordination. The δ-phase adopts the ideal cubic double-perovskite structure, space group Fm ̅3m, with a = 8.5943(1) Å at 400 °C. However, pair distribution function analysis shows that locally the δ-phase is quite different from its long-range average crystal structure. The AlF(6) octahedra undergo large-amplitude rotations which are accompanied by off-center displacements of the K(+) ions that occupy the 12-coordinate A-sites., (© 2011 American Chemical Society)

Novel compounds [Ge(46-x) P(x) ]Te(y) (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate-like structures have been prepared and structurally characterized. They crystallize in the space group Fm ̅3 with the unit cell parameter changing from 20.544(2) to 20.698(2) Å (Z=8) on going from x=13.9 to x=15.6. Their crystal structure is composed of a covalently bonded Ge-P framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type I clathrate superstructure. In contrast to the conventional type I clathrates, [Ge(46-x) P(x) ]Te(y) contain tricoordinated (3b) atoms and no vacancies in the framework positions. As a consequence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first representative of semiclathrates with covalent bonding. A comparison is made with silicon clathrates and the evolution of the crystal structure upon changing the tellurium content is discussed., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hexafluoroacetylacetonates that contain lead and divalent first-row transition metals, PbM(hfac)(4) (M = Ni (1), Co (2), Mn (3), Fe (4), and Zn (5)), have been synthesized. Their heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Compounds 1-5 are highly volatile and decompose below 350 °C. Fluorinated heterometallic β-diketonates have been used for the first time as volatile single-source precursors for the preparation of mixed-metal fluorides. Complex fluorides of composition Pb(2)MF(6) have been obtained by decomposition of 1-5 in a two-zone furnace under low-pressure nitrogen flow. Lead-transition metal fluorides conform to orthorhombically distorted Aurivillius-type structure with layers of corner-sharing [MF(6)] octahedra separated by α-PbO-type (Pb(2)F(2)) blocks. Pb(2)NiF(6) and Pb(2)CoF(6) were found to exhibit magnetic ordering below 80 and 43 K, respectively. The ordering is antiferromagnetic, with a weak, uncompensated moment due to the canting of spins. The Pb(2)MF(6) fluorides represent a new class of prospective magnetoelectric materials combining transition metals and lone-pair main-group cations.

A new A(n)B(n)O(3n-2) homologous series of anion-deficient perovskites has been evidenced by preparation of the members with n = 5 (Pb(2.9)Ba(2.1)Fe(4)TiO(13)) and n = 6 (Pb(3.8)Bi(0.2)Ba(2)Fe(4.2)Ti(1.8)O(16)) in a single phase form. The crystal structures of these compounds were determined using a combination of transmission electron microscopy and X-ray and neutron powder diffraction (S.G. Ammm, a = 5.74313(7), b = 3.98402(4), c = 26.8378(4) Å, R(I) = 0.035, R(P) = 0.042 for Pb(2.9)Ba(2.1)Fe(4)TiO(13) and S.G. Imma, a = 5.7199(1), b = 3.97066(7), c = 32.5245(8) Å, R(I) = 0.032, R(P) = 0.037 for Pb(3.8)Bi(0.2)Ba(2)Fe(4.2)Ti(1.8)O(16)). The crystal structures of the A(n)B(n)O(3n-2) homologues are formed by slicing the perovskite structure with (101)(p) crystallographic shear (CS) planes. The shear planes remove a layer of oxygen atoms and displace the perovskite blocks with respect to each other by the 1/2[110](p) vector. The CS planes introduce edge-sharing connections of the transition metal-oxygen polyhedra at the interface between the perovskite blocks. This results in intrinsically frustrated magnetic couplings between the perovskite blocks due to a competition of the exchange interactions between the edge- and the corner-sharing metal-oxygen polyhedra. Despite the magnetic frustration, neutron powder diffraction and Mössbauer spectroscopy reveal that Pb(2.9)Ba(2.1)Fe(4)TiO(13) and Pb(3.8)Bi(0.2)Ba(2)Fe(4.2)Ti(1.8)O(16) are antiferromagnetically ordered below T(N) = 407 and 343 K, respectively. The Pb(2.9)Ba(2.1)Fe(4)TiO(13) and Pb(3.8)Bi(0.2)Ba(2)Fe(4.2)Ti(1.8)O(16) compounds are in a paraelectric state in the 5-300 K temperature range.

The crystal structures of the beta and gamma polymorphs of Sr(3)WO(6) and the gamma<-->beta phase transition have been investigated using electron diffraction, synchrotron X-ray powder diffraction, and neutron powder diffraction. The gamma-Sr(3)WO(6) polymorph is stable above T(c) approximately 470 K and adopts a monoclinically distorted double perovskite A(2)BB'O(6) = Sr(2)SrWO(6) structure (space group Cc, a = 10.2363(1)A, b = 17.9007(1)A, c = 11.9717(1)A, beta = 125.585(1)(o) at T = 1373 K, Z = 12, corresponding to a = a(p) + 1/2b(p) - 1/2c(p), b = 3/2b(p) + 3/2c(p), c = -b(p) + c(p), a(p),b(p), c(p), lattice vectors of the parent Fm3m double perovskite structure). Upon cooling it undergoes a continuous phase transition into the triclinically distorted beta-Sr(3)WO(6) phase (space group C1, a = 10.09497(3)A, b = 17.64748(5)A, c = 11.81400(3)A, alpha = 89.5470(2)(o), beta = 125.4529(2)(o), gamma = 90.2889(2)(o) at T = 300 K). Both crystal structures of Sr(3)WO(6) belong to a family of double perovskites with broken corner sharing connectivity of the octahedral framework. A remarkable feature of the gamma-Sr(3)WO(6) structure is a non-cooperative rotation of the WO(6) octahedra. One third of the WO(6) octahedra are rotated by approximately 45 degrees about either the b(p) or the c(p) axis of the parent double perovskite structure. As a result, the WO(6) octahedra do not share corners but instead share edges with the coordination polyhedra of the Sr cations at the B positions increasing their coordination number from 6 to 7 or 8. The crystal structure of the beta-phase is very close to the structure of the gamma-phase; decreasing symmetry upon the gamma-->beta transformation occurs because of unequal octahedral rotation angles about the b(p) and c(p) axes and increasing distortions of the WO(6) octahedra.

The crystal structure of a novel compound Pb(13)Mn(9)O(25) has been determined through a direct space structure solution with a Monte-Carlo-based global optimization using precession electron diffraction data (a=14.177(3)A, c=3.9320(7)A, SG P4/m, R(F)=0.239) and compositional information obtained from energy dispersive X-ray analysis and electron energy loss spectroscopy. This allowed to obtain a reliable structural model even despite the simultaneous presence of both heavy (Pb) and light (O) scattering elements and to validate the accuracy of the electron diffraction-based structure refinement. This provides an important benchmark for further studies of complex structural problems with electron diffraction techniques. Pb(13)Mn(9)O(25) has an anion- and cation-deficient perovskite-based structure with the A-positions filled by the Pb atoms and 9/13 of the B positions filled by the Mn atoms in an ordered manner. MnO(6) octahedra and MnO(5) tetragonal pyramids form a network by sharing common corners. Tunnels are formed in the network due to an ordered arrangement of vacancies at the B-sublattice. These tunnels provide sufficient space for localization of the lone 6s(2) electron pairs of the Pb(2+) cations, suggested as the driving force for the structural difference between Pb(13)Mn(9)O(25) and the manganites of alkali-earth elements with similar compositions., (Copyright 2010 Elsevier B.V. All rights reserved.)

The crystal structure of alpha-K(3)AlF(6) was solved and refined from a combination of powder X-ray and neutron diffraction data (a = 18.8385(3)A, c = 33.9644(6)A, S.G. I4(1)/a, Z = 80, R(P)(X-ray) = 0.037, R(P)(neutron) = 0.053). The crystal structure is of the A(2)BB'X(6) elpasolite type with the a = b approximately a(e) square root(5), c = 4a(e) superstructure (a(e), parameter of the elpasolite subcell) and rock-salt-type ordering of the K and Al cations over the B and B' positions, respectively. The remarkable feature of alpha-K(3)AlF(6) is a rotation of 2/5 of the AlF(6) octahedra by approximately pi/4 around one of the crystal axes of the elpasolite subcell, coinciding with the 4-fold symmetry axes of the AlF(6) octahedra. The rotation of the AlF(6) octahedra replaces the corner-sharing between the K and Al polyhedra by edge-sharing, resulting in an increase of coordination numbers of the K cations at the B positions up to 7 and 8. Due to significant deformations of the K polyhedra, the corner-sharing connectivity of the octahedral elpasolite framework is broken and the rotations of the AlF(6) octahedra do not have a cooperative character. Elpasolites and double perovskites with similar structural organization are discussed. The difference in ionic radii of the B and B' cations as well as the tolerance factor are proposed to be the parameters governing the formation of elpasolites and double perovskites with broken corner-sharing connectivity of the octahedral framework.

Heterometallic lead-manganese beta-diketonates have been isolated in pure form by several synthetic methods that include solid-state and solution techniques. Two compounds with different Pb/Mn ratios, PbMn(2)(hfac)(6) (1) and PbMn(hfac)(4) (2) (hfac = hexafluoroacetylacetonate), can be obtained in quantitative yield by using different starting materials. Single crystal X-ray investigation revealed that the solid-state structure of 1 contains trinuclear molecules in which lead metal center is sandwiched between two [Mn(hfac)(3)] units, while 2 consists of infinite chains of alternating [Pb(hfac)(2)] and [Mn(hfac)(2)] fragments. The heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Spectroscopic investigation confirmed the retention of heterometallic structures in solutions of non-coordinating solvents as well as upon sublimation-deposition procedure. Thermal decomposition of heterometallic diketonates has been systematically investigated in a wide range of temperatures and annealing times. For the first time, it has been shown that thermal decomposition of heterometallic diketonates results in mixed-metal oxides, while both the structure of precursors and the thermolysis conditions have a significant influence on the nature of the resulting oxides. Five different Pb-Mn oxides have been detected by X-ray powder diffraction when studying the decomposition of 1 and 2 in the temperature range 500-800 degrees C. The phase that has been previously reported as "Pb(0.43)MnO(2.18)" was synthesized in the pure form by decomposition of 1, and crystallographically characterized. The orthorhombic unit cell parameters of this oxide, obtained by electron diffraction technique, have been subsequently refined using X-ray powder diffraction data. Besides that, a previously unknown lead-manganese oxide has been obtained at low temperature decomposition and short annealing times. The parameters of its monoclinically distorted unit cell have been determined. The EDX analysis revealed that this compound has a Pb/Mn ratio close to 1:4 and contains no appreciable amount of fluorine.

The anion-deficient perovskite 4H-BaMnO(2+x) has been obtained by a topotactic reduction, with LiH, of the hexagonal perovskite 4H-BaMnO(3-x). The crystal structure of 4H-BaMnO(2+x) was solved using electron diffraction and X-ray powder diffraction and further refined using neutron powder diffraction (S.G. Pnma, a = 10.375(2) A, b = 9.466(2) A, c = 11.276(3) A, at 373 K). The orthorhombic superstructure arises from the ordering of oxygen vacancies within a 4H (chch) stacking of close packed c-type BaO(2.5) and h-type BaO(1.5) layers. The ordering of the oxygen vacancies transforms the Mn(2)O(9) units of face-sharing MnO(6) octahedra into Mn(2)O(7) (two corner-sharing tetrahedra) and Mn(2)O(6) (two edge-sharing tetrahedra) groups. The Mn(2)O(7) and Mn(2)O(6) groups are linked by corner-sharing into a three-dimensional framework. The structures of the BaO(2.5) and BaO(1.5) layers are different from those observed previously in anion-deficient perovskites providing a new type of order pattern of oxygen atoms and vacancies in close packed structures. Magnetization measurements and neutron diffraction data reveal 4H-BaMnO(2+x) adopts an antiferromagnetically ordered state below T(N) approximately 350 K.

The brownmillerite-type A 2B 2O 5 structure is considered as a parent one, giving rise to different derivatives: layered double perovskites, A-site and anion-vacancy-ordered perovskites, and the perovskite-like compounds with crystallographic shear planes. The structural relationships and synthesis pathways for these classes of materials are discussed with particular attention to the ordering at the A or B sublattices, anion vacancy ordering, and their mutual interaction.

The new ternary magnesium rhodium boride Mg2Rh1-xB6+2x has been prepared by the reaction of the mixture of Mg powder, RhB, and crystalline boron in a Ta container sealed under argon. The crystal structure of Mg2Rh0.75(1)B6.50(4) is determined using single-crystal X-ray diffraction, electron diffraction, and high-resolution electron microscopy (space group Pbam, a=8.795(2) A, b=11.060(2) A, c=3.5279(5) A, Z=4, 630 reflections, RF=0.045). It represents a modified Y2ReB6 structure type with an unusual replacement of part of the Rh atoms by boron pairs located in the pentagonal channels parallel to the c axis. The pairs interconnect the neighboring planar boron nets into the 3D framework. The variation of the lattice parameters reveals a homogeneity range Mg2Rh1-xB6+2x. The random distribution of the Rh atoms and boron pairs and the stabilizing effect of the boron pairs on the Y2ReB6 type structure motif are discussed using electronic band structure calculations and chemical bonding analysis with the electron localization function (ELF).

Analysis of 102 cases of coagulated hemothorax (CH) are presented: 32--after penetrating wounds and 70--after closed chest injury. In 57% patients with chest wounds and 72% patients with closed injury the cause of CH was to applying late for medical care. Diagnostic value of X-ray, ultrasonic methods, CT and pleural puncture was studied. Depending on the patients state severity, CH volume and stage of it formation conservative treatment, streptase administration, thoracoscopy and thoracotomy with pleurectomy and lung decortication were performed. Lethality was 2.9%.

72 cases of diaphragm's ruptures in patients with serious combined trauma illustrated basic methods of diagnosis in this condition including X-ray, ultrasonic methods, computed tomography and thoracoscopy. In 26.3% of the patients the diagnosis was made during laparotomy or thoracotomy for massive bleeding because of injury of other organs. In the absence of bleeding the diagnosis was based on signs of the abdominal organs dislocation into the pleural cavity. The differential diagnosis between right-sided coagulated hemothorax and diaphragm's right cupula ruptures was the most difficult.

The structures of alpha-Ba(3)RAl(2)O(7.5) and beta-Ba(3)RM(2)O(7.5) complex oxides (R = rare-earth elements, M = Al, Ga) have been studied by a combination of X-ray diffraction, electron diffraction (ED) and high-resolution electron microscopy (HREM). The alpha and beta forms have cell parameters related to the perovskite subcell: a = 2a(per), b = a(per)(2)(1/2), c = 3a(per)(2)(1/2), however, the alpha form has an ortho-rhombic unit cell whereas the beta form adopts monoclinic symmetry. The crystal structure of monoclinic Ba(3)ErGa(2)O(7.5) was refined from X-ray powder data (space group P2/c, a = 7.93617(9), b = 5.96390(7), c = 18.4416(2) Å, beta = 91.325(1) degrees, R(I) = 0.023, R(P) = 0.053), the structure of the alpha form (space group Cmc2(1)) was deduced from ED and HREM data. The important feature of the alpha and beta structures is the presence of slabs containing strings of vertex-sharing tetrahedral Al(2)O(7) pairs. Two almost equivalent oxygen positions within the strings can be occupied either in an ordered manner leading to the low-temperature beta phase or randomly resulting in the high-temperature alpha structure. The critical temperature of this order-disorder phase transition was determined by high-temperature X-ray diffraction and by differential thermal analysis (DTA). In situ ED and HREM observations of the second-order phase transition confirmed the symmetry changes and revealed numerous defects (twins and antiphase boundaries) formed during the phase transformation.