Exploring the full range of N⋯I⋯X halogen-bonding interactions within a single compound using pressure.

The response of the trimethylammonium-iodinechloride and diiodide (TMA-ICl/I2) crystal structures have been examined under high pressure using neutron powder diffraction. TMA-ICl exhibits impressive pressure-driven electronic flexibility, where the N⋯I-Cl interactions progressively encompass all the distances represented in analogous structures recorded in the Cambridge Structural Database. Comparison with the TMA-I2 complex reveals that this flexibility is owed to the electronegativity of the chlorine atom which induces increased distortion of the iodine electron cloud. This structural flexibility may be influential in the future design of functional molecular materials.

Ab initio simulations of α- and ß-ammonium carbamate (NH4·NH2CO2), and the thermal expansivity of deuterated α-ammonium carbamate from 4.2 to 180†K by neutron powder diffraction.

Experimental and computational studies of ammonium carbamate have been carried out, with the objective of studying the elastic anisotropy of the framework manifested in (i) the thermal expansion and (ii) the compressibility; furthermore, the relative thermodynamic stability of the two known polymorphs has been evaluated computationally. Using high-resolution neutron powder diffraction data, the crystal structure of α-ammonium carbamate (ND4·ND2CO2) has been refined [space group Pbca, Z = 8, with a = 17.05189 (15), b = 6.43531 (7), c = 6.68093 (7) Šand V = 733.126 (9) Å3 at 4.2 K] and the thermal expansivity of α-ammonium carbamate has been measured over the temperature range 4.2-180 K. The expansivity shows a high degree of anisotropy, with the b axis most expandable. The ab initio computational studies were carried out on the α- and ß-polymorphs of ammonium carbamate using density functional theory. Fitting equations of state to the P(V) points of the simulations (run athermally) gave the following values: V0 = 744 (2) Å3 and bulk modulus K0 = 16.5 (4) GPa for the α-polymorph, and V0 = 713.6 (5) Å3 and K0 = 24.4 (4) GPa for the ß-polymorph. The simulations show good agreement with the thermoelastic behaviour of α-ammonium carbamate. Both phases show a high-degree of anisotropy; in particular, α-ammonium carbamate shows unusual compressive behaviour, being determined to have negative linear compressibility (NLC) along its a axis above 5 GPa. The thermodynamically stable phase at ambient pressure is the α-polymorph, with a calculated enthalpy difference with respect to the ß-polymorph of 0.399 kJ mol-1; a transition to the ß-polymorph could occur at ∼0.4 GPa.

Crystal and Electronic Structures of A2NaIO6 Periodate Double Perovskites (A = Sr, Ca, Ba): Candidate Wasteforms for I-129 Immobilization.

The synthesis, structure, and thermal stability of the periodate double perovskites A2NaIO6 (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radioiodine. A combination of X-ray diffraction and neutron diffraction, Raman spectroscopy, and DFT simulations were applied to determine accurate crystal structures of these compounds and understand their relative stability. The compounds were found to exhibit rock-salt ordering of Na and I on the perovskite B-site; Ba2NaIO6 was found to adopt the Fm-3m aristotype structure, whereas Sr2NaIO6 and Ca2NaIO6 adopt the P21/n hettotype structure, characterized by cooperative octahedral tilting. DFT simulations determined the Fm-3m and P21/n structures of Ba2NaIO6 to be energetically degenerate at room temperature, whereas diffraction and spectroscopy data evidence only the presence of the Fm-3m phase at room temperature, which may imply an incipient phase transition for this compound. The periodate double perovskites were found to exhibit remarkable thermal stability, with Ba2NaIO6 only decomposing above 1050 °C in air, which is apparently the highest recorded decomposition temperature so far recorded for any iodine bearing compound. As such, these compounds offer some potential for application in the immobilization of iodine-129, from nuclear fuel reprocessing, with an iodine incorporation rate of 25-40 wt%. The synthesis of these compounds, elaborated here, is also compatible with both current conventional and future advanced processes for iodine recovery from the dissolver off-gas.

High-Pressure Study of the Elpasolite Perovskite La2NiMnO6.

Here we report a high-pressure investigation into the structural and magnetic properties of the double perovskite La2NiMnO6 using neutron scattering over a temperature range of 4.2-300 K at ambient pressure and over a temperature range of 120-1177 K up to a maximum pressure of 6.6 GPa. X-ray diffraction was also used up to a maximum pressure of 64 GPa, over a temperature range of 300-720 K. The sample was found to exist in a mixed rhombohedral/monoclinic symmetry at ambient conditions, the balance of which was found to be strongly temperature- and pressure-dependent. Alternating current magnetometry and X-ray absorption near-edge structure measurements were made at ambient pressure to characterize the sample, suggesting that the transition-metal sites exist in a mixed Ni3+/Mn3+ and Ni2+/Mn4+ state at ambient temperature and pressure. Analysis of the magnetic properties of the sample shows that the Curie temperature can be enhanced by ∼12 K with 2 GPa applied pressure, but it is highly stable at pressures beyond this. We report a pressure-volume-temperature equation of state for this material over this combined temperature and pressure range, with an ambient temperature bulk modulus of ∼179(8) GPa. The previously reported transition from monoclinic to rhombohedral symmetry upon heating to 700 K is seen to be encouraged with applied pressure, transforming fully by ∼1.5 GPa. Raman spectroscopy data were collected up to ∼8 GPa and show no clear changes or discontinuities over the reported phase transition to rhombohedral symmetry or any indication of further changes over the range considered. The ambient-pressure Grüneisen parameter γth was determined to be γth = 2.6 with a Debye temperature of 677 K. The individual modal parameters γj at ambient temperature were also determined from the high-pressure Raman data.

Structure and physical properties of SeCo1-x Mn x O3.

We describe the high-pressure (4 GPa) high-temperature (∼1100 K) synthesis of the solid solution series SeCo1-x Mn x O3 (0 < x < 1) using H2SeO4 and transition metal oxide mixtures sealed in Pt capsules. Neutron powder diffraction has been performed to determine progression of the structure across the solution. All samples crystallise with orthorhombic Pnma symmetry, and octahedral tilting is determined to increase with Mn content. SQUID magnetometry measurements were performed, and reveal that the Néel temperature shifts only by approximately 1 K over the series.

Crystal structures and electronic properties in 3d transition metal doped SrRuO3.

The synthesis of polycrystalline samples of B-site doped SrRu1-xMxO3 with x≤ 0.2 by solid state methods is described for a number of dopants (M = Mg, Mn, Fe, Co, Ni, Cu, or Zn) and the structures of these established using Synchrotron X-ray powder diffraction, and for SrRu0.8Cu0.2O3 high resolution neutron diffraction. With the exception of M = Cu, samples with x = 0.2 form an orthorhombic Pbnm type perovskite structure at room temperature and these exhibit a sequence of phase transitions upon heating associated with the gradual reduction in the cooperative tilting of the corner sharing octahedra. SrRu0.8Cu0.2O3 forms a unique monoclinic structure at low temperatures and this transforms to the cubic Pm3[combining macron]m structure via an I4/mcm intermediate upon heating. The magnetic and electronic properties of the samples have been studied. Doping results in a decrease in the Curie temperature and at x = 0.2 all the samples are insulators. This is a consequence of the partial oxidation of the Ru cation that narrows the Ru 4d bands coupled with the suppression of the itinerant nature of the Ru 4d electrons due to the random distribution of the dopant cations. Ru L3-edge X-ray absorption spectroscopy of the Cu doped samples reveal a gradual increase in the average Ru oxidation sate upon doping. Electrical resistivity measurements show that doping increases the resistivity of the samples, and the temperature dependence of the resistivities are consistent with Arrhenius-type charge conduction.

X-ray and neutron powder diffraction analyses of Gly·MgSO4·5H2O and Gly·MgSO4·3H2O, and their deuterated counterparts.

We have identified a new compound in the glycine-MgSO4-water ternary system, namely glycine magnesium sulfate trihydrate (or Gly·MgSO4·3H2O) {systematic name: catena-poly[[tetraaquamagnesium(II)]-µ-glycine-κ(2)O:O'-[diaquabis(sulfato-κO)magnesium(II)]-µ-glycine-κ(2)O:O']; [Mg(SO4)(C2D5NO2)(D2O)3]n}, which can be grown from a supersaturated solution at ∼350 K and which may also be formed by heating the previously known glycine magnesium sulfate pentahydrate (or Gly·MgSO4·5H2O) {systematic name: hexaaquamagnesium(II) tetraaquadiglycinemagnesium(II) disulfate; [Mg(D2O)6][Mg(C2D5NO2)2(D2O)4](SO4)2} above ∼330 K in air. X-ray powder diffraction analysis reveals that the trihydrate phase is monoclinic (space group P21/n), with a unit-cell metric very similar to that of recently identified Gly·CoSO4·3H2O [Tepavitcharova et al. (2012). J. Mol. Struct. 1018, 113-121]. In order to obtain an accurate determination of all structural parameters, including the locations of H atoms, and to better understand the relationship between the pentahydrate and the trihydrate, neutron powder diffraction measurements of both (fully deuterated) phases were carried out at 10 K at the ISIS neutron spallation source, these being complemented with X-ray powder diffraction measurements and Raman spectroscopy. At 10 K, glycine magnesium sulfate pentahydrate, structurally described by the `double' formula [Gly(d5)·MgSO4·5D2O]2, is triclinic (space group P-1, Z = 1), and glycine magnesium sulfate trihydrate, which may be described by the formula Gly(d5)·MgSO4·3D2O, is monoclinic (space group P21/n, Z = 4). In the pentahydrate, there are two symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two SO4 tetrahedra with site symmetry 1. The octahedra comprise one [tetraaquadiglcyinemagnesium](2+) ion (centred on Mg1) and one [hexaaquamagnesium](2+) ion (centred on Mg2), and the glycine zwitterion, NH3(+)CH2COO(-), adopts a monodentate coordination to Mg2. In the trihydrate, there are two pairs of symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two pairs of SO4 tetrahedra with site symmetry 1; the glycine zwitterion adopts a binuclear-bidentate bridging function between Mg1 and Mg2, whilst the Mg2 octahedra form a corner-sharing arrangement with the sulfate tetrahedra. These bridged polyhedra thus constitute infinite polymeric chains extending along the b axis of the crystal. A range of O-H...O, N-H...O and C-H...O hydrogen bonds, including some three-centred interactions, complete the three-dimensional framework of each crystal.

Neutron diffraction and multinuclear solid state NMR investigation into the structures of oxide ion conducting La9.6Si6O26.4 and La8Sr2Si6O26, and their hydrated phases.

Apatite silicates are attracting significant interest as potential SOFC electrolyte materials. They are non-conventional oxide ion conductors in the sense that oxide ion interstitials, rather than vacancies, are the key defects. In this work we compare the structures of La9.6Si6O26.4 and La8Sr2Si6O26, both before and after hydration in order to gather information about the location of the interstitial oxide ion site. Neutron diffraction structural studies suggest that in the as-prepared La8Sr2Si6O26 and hydrated La8Sr2Si6O26, the interstitial oxide ion sites are close to the apatite channel centre. For La9.6Si6O26.4, a similar site close to the channel centre is observed, but on hydration of this particular sample, the interstitial site is shown to be significantly displaced away from the channel centre towards the SiO4 units. This can be explained by the need for additional displacement from the channel centre to accommodate the large amount of interstitial anions in this hydrated phase. The solid state (29)Si MAS NMR spectra are shown to be very sensitive to the different speciation exhibited by the La8Sr2Si6O26 and La9.6Si6O26.4 systems, with the former being dominated by regular SiO4 framework species and the latter being dominated by interruptions to this network caused by cation vacancies and interstitials. The corresponding (17)O MAS NMR study identifies a strong signal from the O atoms of the SiO4 groups, thus demonstrating that all of the O species in these systems are exchangeable O under heterogeneous gas phase conditions. In addition, interstitial O species attributed to pendant OH linkages on the Si positions are clearly identified and resolved, and these are removed on dehydration. This observation and assignment is corroborated by corresponding (1)H MAS NMR measurements. Overall the neutron diffraction work indicates that the interstitial site location in these apatite silicates depends on the anion content with progressive displacement towards the SiO4 tetrahedra on increasing anion content, while the observation of exchangeable O on the SiO4 groups is consistent with prior modelling predictions as to the importance on the silicate units in the conduction process.

Low temperature structural studies of SrSnO3.

High resolution powder neutron diffraction measurements on polycrystalline SrSnO3 between 8 and 350 K are described. SrSnO3 retains the orthorhombic Pbnm structure over this temperature range. Examination of the thermal expansion of the individual lattice parameters reveals an anomaly near 230 K that may reflect the presence of polar nanodomains associated with local disorder of the octahedral tilts.

Thermoelastic and structural properties of ionically conducting cerate perovskites: (II) SrCeO3 between 1273 K and 1723 K.

The temperature dependence of the crystal structure and the thermoelastic properties of SrCeO(3) have been determined from Rietveld refinement of high resolution, neutron time-of-flight powder diffraction data collected in 5 K intervals between 1273 K and 1723 K. No evidence was found for critical behaviour in the amplitudes of the modes that soften in zone boundary phase transitions in perovskite-structured phases suggesting SrCeO(3) may remain orthorhombic, space group Pbnm from 1.2 K up to the 1 atm melting point of 2266 K. The temperature variation of the crystal structure has been determined from mode decomposition techniques and the structural evolution has been inferred from the temperature-dependences of the spontaneous shear strain and the order parameter associated with the anti-phase tilt. Thermoelastic properties have been derived from the temperature variation of the unit cell, isobaric heat capacity, and atomic displacement parameters and shows good agreement with earlier work carried out on the lightly doped system SrCe(0.95)Yb(0.05)O(ξ) (ξ∼ 3). Temperature-dependent corrections for the bond valence parameters for strontium and cerium are reported.

Structural and dielectric studies of the phase behaviour of the topological ferroelectric La1-xNdxTaO4.

The layered perovskite LaTaO(4) has been prepared in its polar orthorhombic polymorphic form at ambient temperature. Although no structural phase transition is observed in the temperature interval 25° C < T < 500 °C, a very large axial thermal contraction effect is seen, which can be ascribed to an anomalous buckling of the perovskite octahedral layer. The non-polar monoclinic polymorph can be stabilised at ambient temperature by Nd-doping. A composition La(0.90)Nd(0.10)TaO(4) shows a first-order monoclinic-orthorhombic (non-polar to polar) transition in the region 250° C < T < 350 °C. Dielectric responses are observed at both the above structural events but, despite the 'topological ferroelectric' nature of orthorhombic LaTaO(4), we have not succeeded in obtaining ferroelectric P-E hysteresis behaviour. Structural relationships in the wider family of A(n)B(n)X(3n+2) layered perovskites are discussed.

Introducing a large polar tetragonal distortion into Ba-doped BiFeO3 by low-temperature fluorination.

This article reports on the synthesis and crystallographic and magnetic structure of barium-doped BiFeO3 compounds with approximate composition Bi(1-x)Ba(x)FeO(3-x/2), as well as those of the fluorinated compounds Bi(1-x)Ba(x)FeO(3-x)F(x) (both with x = 0.2, 0.3), prepared by low-temperature fluorination of the oxide precursors using polyvinylidenedifluoride. Whereas the oxide compounds were obtained as cubic (x = 0.2) and slightly tetragonal (x = 0.3, c/a ≈ 1.003) distorted perovskite compounds, a large tetragonal polar distortion was observed for the oxyfluoride compounds (c/a ≈ 1.08 for x = 0.2 and ∼1.05 for x = 0.3), being isostructural to tetragonal PbTiO3. Although described differently in previous reports on Ba-doped BiFeO3, the observed remanent magnetization is found to agree well with the amount of BaFe12O19 only detectable by neutron diffraction and the well-known magnetic properties of BaFe12O19. The oxyfluoride compounds show G-type antiferromagnetic ordering with magnetic moments lying in the a/b plane.

Tuning the giant magnetoelastic transition in Ba3BiIr2O9 and Ba3BiRu2O9.

We have experimentally investigated the effects of pressure on the magnetoelastic transitions associated with the opening of spin-gaps in Ba3BiIr2O9 and Ba3BiRu2O9. For both compounds, reducing the unit cell volume by either external physical and internal chemical pressure was found to reduce the temperature T(*) of the transition and, to a lesser extent, the magnitude of the associated negative thermal volume expansion. The results yield the latent heat associated with the transitions, -3.34(3) × 10(2) J mol(-1) for Ba3BiIr2O9 and -7.1(5) × 10(2) J mol(-1) for Ba3BiRu2O9. The transition in Ba3BiRu2O9 is significantly more robust than in Ba3BiIr2O9, requiring an order of magnitude higher pressures to achieve the same reduction in T(*). The differing responses of the two compounds points to differences between the 4d and 5d metals and hence to the importance of spin-orbit coupling, which is expected to be much stronger in the Ir compound.

Crystallographic and magnetic structure of the perovskite-type compound BaFeO2.5: unrivaled complexity in oxygen vacancy ordering.

We report here on the characterization of the vacancy-ordered perovskite-type structure of BaFeO2.5 by means of combined Rietveld analysis of powder X-ray and neutron diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c [a = 6.9753(1) Å, b = 11.7281(2) Å, c = 23.4507(4) Å, ß = 98.813(1)°, and Z = 28] containing seven crystallographically different iron atoms. The coordination scheme is determined to be Ba7(FeO4/2)1(FeO3/2O1/1)3(FeO5/2)2(FeO6/2)1 = Ba7Fe([6])1Fe([5])2Fe([4])4O17.5 and is in agreement with the (57)Fe Mössbauer spectra and density functional theory based calculations. To our knowledge, the structure of BaFeO2.5 is the most complicated perovskite-type superstructure reported so far (largest primitive cell, number of ABX2.5 units per unit cell, and number of different crystallographic sites). The magnetic structure was determined from the powder neutron diffraction data and can be understood in terms of "G-type" antiferromagnetic ordering between connected iron-containing polyhedra, in agreement with field-sweep and zero-field-cooled/field-cooled measurements.

On the soft magnetic properties of the compounds of the series Na(x)Mn(4.5-x/2)(VO4)3 and the magnetic structure of h.t.-Mn3(VO4)2 (x = 1).

The high temperature phase of manganese vanadate h.t.-Mn3(VO4)2 and the solid solution with NaMn4(VO4)3 (Na(x)Mn(4.5-x/2)(VO4)3) were shown to order ferrimagnetically below 55 K for x < 1, whereas NaMn4(VO4)3 is an antiferromagnet. The materials show very soft magnetic properties with low coercitive fields required for demagnetisation (Hc < 0.001 T). The magnetic structure of h.t.-Mn3(VO4)2 was determined by Rietveld analysis of low temperature powder neutron diffraction data, and shows antiferromagnetic alignment of the magnetic moments of the Mn(2+) ions on the 8c and 8d sites. The ferrimagnetic moments were shown to result from the magnetic moments of the Mn(2+) cations located on the 4b site in unusual dodecahedral coordination (Hoard dodecahedron). This coordination can be understood as two penetrating oxygen coordination tetrahedra, one showing shorter and one showing longer Mn-O distances. The magnetic moments of the Mn(2+) ions on the 4b site are aligned parallel to the ones on 8d and antiparallel to the ones on 8c, being in good agreement with the GKA rules. The local exchange interactions between the Mn(2+) ions on the 4b to those on the 8c/8d sites are likely to be similar in strength and competitive and therefore probably contribute to the soft magnetic properties.

Giant magnetoelastic effect at the opening of a spin-gap in Ba3BiIr2O9.

As compared to 3d (first-row) transition metals, the 4d and 5d transition metals have much more diffuse valence orbitals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are correspondingly rare in 4d and 5d compounds. Here, we show that the 6H-perovskite Ba(3)BiIr(2)O(9), which contains 5d Ir(4+) (S = 1/2) dimerized into isolated face-sharing Ir(2)O(9) bioctahedra, exhibits a giant magnetoelastic effect, the largest of any known 5d compound, associated with the opening of a spin-gap at T* = 74 K. The resulting first-order transition is characterized by a remarkable 4% increase in Ir-Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimizes direct Ir-Ir bonding (at high temperature), and one that optimizes Ir-O-Ir magnetic superexchange (at low temperature).

Negative linear compressibility and massive anisotropic thermal expansion in methanol monohydrate.

The vast majority of materials shrink in all directions when hydrostatically compressed; exceptions include certain metallic or polymer foam structures, which may exhibit negative linear compressibility (NLC) (that is, they expand in one or more directions under hydrostatic compression). Materials that exhibit this property at the molecular level--crystalline solids with intrinsic NLC--are extremely uncommon. With the use of neutron powder diffraction, we have discovered and characterized both NLC and extremely anisotropic thermal expansion, including negative thermal expansion (NTE) along the NLC axis, in a simple molecular crystal (the deuterated 1:1 compound of methanol and water). Apically linked rhombuses, which are formed by the bridging of hydroxyl-water chains with methyl groups, extend along the axis of NLC/NTE and lead to the observed behavior.

The polar phase of NaNbO(3): a combined study by powder diffraction, solid-state NMR, and first-principles calculations.

A polar phase of NaNbO(3) has been successfully synthesized using sol-gel techniques. Detailed characterization of this phase has been undertaken using high-resolution powder diffraction (X-ray and neutron) and (23)Na multiple-quantum (MQ) MAS NMR, supported by second harmonic generation measurements and density functional theory calculations. Samples of NaNbO(3) were also synthesized using conventional solid-state methods and were observed to routinely comprise of a mixture of two different polymorphs of NaNbO(3), namely, the well-known orthorhombic phase (space group Pbcm) and the current polar phase, the relative quantities of which vary considerably depending upon precise reaction conditions. Our studies show that each of these two polymorphs of NaNbO(3) contains two crystallographically distinct Na sites. This is consistent with assignment of the polar phase to the orthorhombic space group P2(1)ma, although peak broadenings in the diffraction data suggest a subtle monoclinic distortion. Using carefully monitored molten salt techniques, it was possible to eradicate the polar polymorph and synthesize the pure Pbcm phase.

Polysomatic apatites.

Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A(5N)B(3N)O(9N + 6)X(Ndelta) (2 < or = N < or = infinity) that is built by condensing N apatite modules (A(5)B(3)O(18)X(delta)) in configurations to create B(n)O(3n + 1) (1 < or = n < or = infinity) tetrahedral chains. Hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)] typifies a widely studied polysome where N = 2 and the tetrahedra are isolated in A(10)(BO(4))(6)X(2) compounds, but N = 3 A(15)(B(2)O(7))(3)(BO(4))(3)X(3) (ganomalite) and N = 4 A(20)(B(2)O(7))(6)X(4) (nasonite) are also known, with the X site untenanted or partially occupied as required for charge balance. The apatite modules, while topologically identical, are often compositionally or symmetrically distinct, and an infinite number of polysomes is feasible, generally with the restriction being that an A:B = 5:3 cation ratio be maintained. The end-members are the N = 2 polysome with all tetrahedra separated, and N = infinity, in which the hypothetical compound A(5)B(3)O(9)X contains infinite, corner-connected tetrahedral strings. The principal characteristics of a polysome are summarized using the nomenclature apatite-(A B X)-NS, where A/B/X are the most abundant species in these sites, N is the number of modules in the crystallographic repeat, and S is the symmetry symbol (usually H, T, M or A). This article examines the state-of-the-art in polysomatic apatite synthesis and crystallochemical design. It also presents X-ray and neutron powder diffraction investigations for several polysome chemical series and examines the prevalence of stacking disorder by electron microscopy. These insights into the structure-building principles of apatite polysomes will guide their development as functional materials.

X-ray absorption and neutron diffraction studies of (Sr(1 - x)Ce(x))MnO3: transition from coherent to incoherent static Jahn-Teller distortions.

We have carried out Ce L- and Mn K-edge x-ray absorption near edge structure (XANES) measurements to experimentally determine the oxidation states of both Ce and Mn in (Sr(1 - x)Ce(x))MnO(3) (x = 0.1-0.4). It was found that although Ce is predominantly 4 + at low doping levels (x = 0.1 and 0.15), the Ce valency decreases with increasing Ce doping (reaching a value of around 3.5 + at x = 0.4). The average Mn oxidation state decreases with the increase of Ce content, with the percentage of Jahn-Teller active Mn(3+) ions increasing from 26% (x = 0.1) to 57% (x = 0.4). Precise structural parameters were also obtained from high resolution neutron diffraction studies for samples with x = 0.1-0.3. The crystal structure remains tetragonal in I4/mcm for x ≤ 0.3. The octahedral tilt angle increases with increasing Ce content, but the distortion of the MnO(6) octahedra is reduced significantly at x ≥ 0.2 due to a transition from long-range ordered Jahn-Teller distortions to incoherent static distortions.