Showing papers on "Crystal published in 1995"
TL;DR: In this article, a nonlinear optical crystal CsLiB6O10 (CLBO) is described that can be grown from either stoichiometric melt or from solution, and a large, high quality single crystal with dimensions of 14×11×11 cm3 was obtained by the top-seeded Kyropoulos method.
Abstract: A new nonlinear optical crystal CsLiB6O10 (CLBO), is described that can be grown from either stoichiometric melt or from solution. A large, high quality single crystal with dimensions of 14×11×11 cm3 was obtained by the top‐seeded Kyropoulos method. Fourth harmonic and fifth harmonic generations of the 1.064 μm Nd:YAG laser radiation with type‐I phase matching were realized in the CLBO crystal. Output pulse energies obtained were 110 mJ at 266 nm and 35 mJ at 213 nm.
563 citations
30 Jan 1995
TL;DR: In this paper, a new nonlinear optical (NLO) crystal, CsLiB6O10 (CLBO) has been discovered, which can quadruple and quintuple the Nd:YAG laser output.
Abstract: A new nonlinear optical (NLO) crystal, CsLiB6O10 (CLBO) has been discovered. CLBO can quadruple and quintuple the Nd:YAG laser output. Large CLBO crystal with dimensions 13×12×10 cm3 could be grown in twelve days.
512 citations
TL;DR: The properties of an oxyfluoride glass ceramic that possesses high transparency after ceramming are described in this paper, where it is shown that a significant fraction of the rare earth dopant is preferentially partitioned into the fluoride crystal phase.
Abstract: The properties of an oxyfluoride glass ceramic that possesses high transparency after ceramming are described. Approximately 25 vol % of this material is comprised of cubic, fluoride nanocrystals and the remainder is a predominantly oxide glass. When doped with Pr+3, the fluorescence lifetime at 1300 nm is longer than in a fluorozirconate glass, suggesting that a significant fraction of the rare‐earth dopant is preferentially partitioned into the fluoride crystal phase. This material has the added advantage of being compatible with ambient air processing.
293 citations
TL;DR: In this article, a new layered material belonging to the ternary M2X2Te6 chalcogenides family was synthesized from a stoichiometric mixture of the elements and heated in a sealed evacuated quartz tube for 20 d at 700 degrees C.
Abstract: Cr2Ge2Te6 is a new layered material belonging to the lamellar ternary M2X2Te6 chalcogenides family (where M is a 3+ oxidation state metal and X2 a silicon or a germanium pair). It was synthesized from a stoichiometric mixture of the elements and heated in a sealed evacuated quartz tube for 20 d at 700 degrees C. The crystal symmetry is rhombohedral, of space group R3, with the following hexagonal cell parameters: a=b=0.68275(4) nm, c=2.05619(9) nm, V=0.830 1(1) nm3 and Z=3. The crystal structure of Cr2Ge2Te6 was solved using both X-ray single-crystal diffraction and neutron powder diffraction data. Growth defects were detected and investigated using high-resolution electron microscopy. The magnetic structure and properties of Cr2Ge2Te6 have been determined by neutron powder diffraction and susceptibility and magnetization measurements. Below 61 K, Cr2Ge2Te6 is ferromagnetic with spins aligned along the c axis of the cell ( mu (Cr3+)=2.80(4)mu B at 5 K). The thermal evolution of the magnetic moments below Tc is given. At room temperature, Cr2Ge2Te6 presents a rho =0.02 Omega cm resistivity. Above Tc, the thermal evolution of the resistivity can be fitted as rho =exp(A/kT), where A=0.2 eV. Band-structure and crystal orbitals of Cr2Ge2Te6 have been calculated using the extended Huckel method and indicate no gap but highly localized Cr 3d states, giving evidence of a hopping mechanism for Cr2Ge2Te6, electrical conductivity.
264 citations
TL;DR: In this paper, the lattice parameters of the poly(tetramethylene succinate) (PBS) were determined from the electron diffraction patterns of the single crystals and stretched films.
Abstract: Crystals of an aliphatic polyester, poly(tetramethylene succinate) (PBS) are investigated using transmission electron microscopy. Single crystals grown from a 0.01 wt % dichlorobenzene solution show a terrace-like morphology above 65 °C and a leaflike one at lower temperatures. The molecules are packed perpendicular to the basal plane of the single crystals, and twin crystals with a (110) twin plane are frequently observed. The thickness of the single crystal lamellae increases smoothly with increasing crystallization temperature. Lattice parameters of the PBS crystal in the monoclinic unit cell are determined from the electron diffraction patterns of the single crystals and stretched films as a = 0.523 nm, b = 0.908 nm, c = 1.079 nm, and β = 123.87°. The dimension of the c-axis is shorter than the value calculated from a fully extended chain conformation, as has already been found for other aliphatic polyesters. Two types of negative spherulites are observed according to growth temperature.
238 citations
TL;DR: The dynamics of domain growth has been directly observed for the first time with a resolution of 10 nm and the origin of the domain contrast in the topographic of AFM images is explained by the piezoelectric deformation of the crystal surface in the internal electric field.
Abstract: The nanoscale visualization and control of domain structure with atomic force microscopy (AFM) in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate is reported. The origin of the domain contrast in the topographic of AFM images is explained by the piezoelectric deformation of the crystal surface in the internal electric field. The domain structure was modified by applying a voltage to the conductive AFM tip. The dynamics of domain growth has been directly observed for the first time with a resolution of 10 nm.
229 citations
TL;DR: In this paper, the main results of these covalent interactions are shifts of energy levels out of (or into) the gap and new optical activity (infrared absorption and Raman scattering).
Abstract: Hydrogen is a common impurity in all semiconductors. Although it is sometimes deliberately introduced, hydrogen often penetrates into the crystal during device processing. It interacts with broken or weak covalent bonds, such as those found at extended and localized defect centers. The main results of these covalent interactions are shifts of energy levels out of (or into) the gap and new optical activity (infrared absorption and Raman scattering). The shifts in energy levels lead to the passivation (or activation) of the electrical activity of various centers. Hydrogen can also interact with the perfect crystal and with itself, sometimes leading to the formation of extended structures known as platelets. Finally, H also acts as a catalyst, dramatically enhancing the diffusivity of interstitial oxygen in Si. The consequences of these interactions are substantial changes in the electrical and optical properties of the crystal, and in the lifetime of charge carriers. The thermal stability of the complexes containing hydrogen varies from room temperature up to several hundreds of degrees Celsius, and the diffusion of H is trap-limited up to rather high temperatures. Hydrogen normally exists in more than one configuration and charge state in semiconductors. A range of experimental and theoretical techniques have been used to investigate the rich properties of hydrogen in semiconductors, and several extensive reviews focusing mostly on the experimental side of these issues have been published in the past five years. The present review focuses mostly on the theoretical work performed in this field. However, the most recent experimental results are also discussed, and the current understanding of hydrogen interactions in semiconductors summarized.
189 citations
TL;DR: In this article, a theoretical approach was proposed to predict needle-like shape of growing urea crystals from aqueous solution, which is consistent with experimental observations. But this approach was only applied to the case of urea crystal grown from urea.
Abstract: PREDICTING the shape of growing crystals is important for industrial crystallization processes. The equilibrium form of a crystal can be determined unambiguously from a consideration of the surface free energies of the various crystallographic faces {hkl}1, but the growth morphology is determined by kinetic factors which are harder to predict. This morphology depends on the relative growth rates R rel hkl of the crystal faces. Several theories have been advanced2,3 to relate R rel hkl to geometric or energetic characteristics of the surfaces {hkl}, but these have met with limited success in predicting the crystal morphologies observed. Here we present a theoretical approach to the problem in which R rel hkl is determined by quantities that are accessible either from kinetic models or from computer simulations of the solid-fluid interface. The important parameters controlling the growth rate are the energy required to create a step at the crystal surface and the free-energy barrier for an adsorbed solute molecule to be incorporated into the crystal. Both can be related to the mole fraction of adsorbed solute molecules in dynamic equilibrium with those in the crystal surface. When this approach is applied to the case of urea crystals grown from aqueous solution, we predict a needle-like shape which is consistent with experimental observations.
188 citations
TL;DR: In this article, the topology of the electron density within the theory of atoms in crystals has been used to define primary and secondary interactions in terms of the topological properties of crystal lattices.
Abstract: The heavier halide molecules form layered crystals indicative of the presence of a specific directed intermolecular interaction. It is shown that this interaction within the crystal can be defined and characterized using the topology of the electron density within the theory of atoms in crystals. It is also shown that its presence in the crystal and the resulting geometry of the layered structure can be predicted in terms of the topology of the Laplacian distribution of an isolated Cl2 molecule, as it relates to the definition of Lewis acid and base sites within the valence shell of an atom. The generality of the definition of both primary and secondary interactions in terms of the topology of the electron density is demonstrated for all types of crystal. The electron density of solid molecular chlorine was determined by fitting the experimental X-ray structure factors and by theoretical calculation and its topology determined. Each Cl atom is found to be linked by bond paths, lines of maximum electron density, to twelve other atoms in the crystal: to four atoms in the same layer parallel to the bc plane, one of which defines the intramolecular bond of the Cl2 group, to six atoms in the four neighbouring molecules lying in the same stack parallel to the b axis and to two atoms in molecules situated in a neighbouring stack.
180 citations
TL;DR: The comparison of the structures of the same membrane protein in two different packing environments reveals that the overall structure of OmpF is not influenced by crystal lattice constraints and, thus, presumably bears close resemblance to the in vivo structure.
172 citations
01 Jan 1995
TL;DR: In this paper, the authors present an overview of the history of the field of crystal growth and its applications in physics and chemistry. But their focus is on the physical aspects of the growth process and not the theoretical aspects.
Abstract: Science and Technology of Crystal Growth: An Introduction J. P. van der Eerden, O. S. L. Bruinsma. 1: Classical and Statistical Thermodynamics. 1.1. Thermodynamics and Phase Diagrams - Fundamentals and Tools for Crystal Growth G. Krabbes. 1.2. Atomic Models for Crystal Growth J. P. van der Eerden. 1.3. The Syncrystallization of Thianaphthene and Naphthalene, an Exercise in Thermodynamic Phase Diagram Analysis H. A. J. Oonk. 1.4. From Thermoelasticity to Surface Melting T. H. M. van den Berg, J. P. van der Eerden. 2: Crystallization Concepts. 2.1. Nucleation D. Kashchiev. 2.2. Topics in Crystal Growth Kinetics A. A. Chernov, H. Komatsu. 2.3. Lattice Growth Models J. I. D. Alexander. 2.4. Macroscopic Transport Processes during the Growth of Single Crystals from the Melt J. J. Derby. 3: Single Crystals and Epitaxy. 3.1. Large-Scale Numerical Modeling of the Bulk Crystal Growth from the Melt and Solution J. J. Derby, S. Kuppurao, Q. Xiao, A. Yeckel, Y. Zhou. 3.2. Vapour Growth G. Krabbes. 3.3. Advanced Epitaxial Growth Techniques for III-V Materials I. Moerman, P. Demeester. 4: Crystal Shape. 4.1. Morphology of Crystals: Past and Future P. Bennema. 4.2. Modulated and Quasicrystals H. Meekes. 4.3. Modelling the Habit Modification of Molecular Crystals by the Action of 'Tailor-Made' Additives G. Clydesdale, K. J. Roberts. 4.4. Morphological Instability: Dendrites, Seaweed and Fractals K. Kassner. 5: Mass Crystallization. 5.1. Mass Crystallization, Number Balances and Size Distributions J. Garside. 5.2. Crystallizers G. Hofmann. 5.3. Melt Suspension Crystallization M. Matsuoka. 5.4. Melt Layer Crystallization J. Ulrich, J. Bierwirth. 5.5. Secondary Nucleation G. M. van Rosmalen, A. E. van der Heyden. 6: Crystals Grown from Large Growth Units. 6.1. Crystallization in Colloidal Suspensions J. S. van Duijneveldt, H. N. W. Lekkerkerker. 6.2. Polytopism and Inorganic Crystal Growth and Reactivity A. Baronnet. 6.3. Polymer Crystallization G. Goldbeck-Wood. 6.4. Principles of Crystal Growth in Protein Crystallization A. A. Chernov, H. Komatsu. 7: Surface Structure. 7.1. Some Common Pathologies in Step Growth: Impurities and Surface Reconstruction W. J. P. van Enckevort. 7.2. Characterization of Crystal Growth Processes Using Synchrotron X-Ray Techniques K. J. Roberts. 7.3. Optical and Scanning Probe Microscopy K. Tsukamoto. Subject Index.
TL;DR: Differential scanning calorimetry (DSC) was used to analyze the crystal distribution in homogeneous ethylene-octene copolymers polymerized by the constrained geometry catalyst technology (CGCT).
Abstract: Differential scanning calorimetry (DSC) was used to analyze the crystal distribution in homogeneous ethylene–octene copolymers polymerized by the constrained geometry catalyst technology (CGCT). To minimize ambiguities from thermal history effects, copolymers were isothermally annealed at temperatures within the melting range. The cumulative crystallinity was related to the crystal distribution by the Gibbs–Thomson equation. The results provided a clear distinction between Type I copolymers (density less than 0.89 g/cc) and Type II copolymers (densities between 0.89 and 0.91 g/cc). The former had a singlecrystal population that was identified with the bundled crystals seen in transmission electron micrographs. In comparison, the latter had two crystal populations that correlated with lamellar crystals and bundled crystals. © 1995 John Wiley & Sons, Inc.
TL;DR: The thermal conductivity of the Nd : GdVO4 crystal (atomic neodymium concentration 1.3%) was determined in the temperature range 77-300 K as mentioned in this paper.
Abstract: The refractive indices of new Nd3+ : GdVO4, Tm3+ : GdVO4, and Er3+ : GdVO4 laser crystals were determined with an error of ±5×10-5 in the range 400–1100 nm. The birefringence of these crystals was on the average 0.24, and the dispersion was described by the formula 1/Δn2 = a+ b/λ2. The thermal conductivity of the Nd : GdVO4 crystal (atomic neodymium concentration 1.3%) was determined in the temperature range 77-300 K. At 300 K the conductivity along the direction was 11.7 W m-1 K-1, which was higher than the conductivity of Nd : YAG crystals.
TL;DR: In this paper, an increase in the alumina concentration was found to decrease the crystal growth rate, the number of crystals produced, and the ZSM-5 yield, in the range 130-230 nm with a narrow particle size distribution.
TL;DR: A method for minimizing the lattice energy of molecular crystal structures, using a realistic anisotropic atom–atom model for the intermolecular forces, and shows that it provides a promising new approach to studying the crystal packing of polar molecules.
Abstract: We describe a method for minimizing the lattice energy of molecular crystal structures, using a realistic anisotropic atom-atom model for the intermolecular forces. Molecules are assumed to be rigid, and the structure is described by the center of mass positions and orientational parameters for each molecule in the unit cell, as well as external strain parameters used to optimize the cell geometry. The resulting program uses a distributed multipole description of the electrostatic forces, which consists of sets of atomic multipoles (charge, dipole, quadrupole, etc.) to represent the lone pair, pi electron density, and other nonspherical features in the atomic charge distribution. Such ab initio based, electrostatic models are essential for describing the orientation dependence of the intermolecular forces, including hydrogen bonding, between polar molecules. Studies on a range of organic crystals containing hydrogen bonds are used to illustrate the use of this new crystal structure relaxation program, DMAREL, and show that it provides a promising new approach to studying the crystal packing of polar molecules. (C) 1995 by John Wiley and Sons, Inc.
TL;DR: In this article, the spin-lattice coupling coefficient G(11) for Mn2+ in the cubic phase of a CsCaCl3 crystal has been calculated from the three microscopic mechanisms which contribute to zero-field splitting.
Abstract: In this paper, the spin-lattice coupling coefficient G(11) for Mn2+ in the cubic phase of a CsCaCl3 crystal has been calculated from the three microscopic mechanisms which contribute to zero-field splitting. Based on this, the local rotation angle phi(T) for Mn2+ in the tetragonal phase of a CsCaCl3 crystal is estimated from the EPR zero-held splitting b(2)(0)(T). The reasonableness of the local rotation angle is discussed.
TL;DR: In this article, the crystal structures of MgAl 2 O 4 spinel single crystals irradiated to high neutron fluences (> 5 x 10 26 n/m 2 (E n > 0.1 MeV)), were examined by neutron diffraction.
Patent•
21 Dec 1995TL;DR: Trench structures (12,32,35,46) as mentioned in this paper are formed in single crystal silicon substrates (10,30) that have either a (110) or (112) orientation.
Abstract: Trench structures (12,32,35,46) are formed in single crystal silicon substrates (10,30) that have either a (110) or (112) orientation. A selective wet etch solution is used that removes only the exposed portions of the single crystal silicon substrates (10,30) that are in the (110) or (112) crystal planes. The trench structures (12,32,35,46) are defined by the {111} crystal planes in the single crystal silicon substrate (10,30) that are exposed during the selective wet etch process. Trench structures (32,35) can be formed on both sides of a single crystal silicon substrate (30) to form an opening (34). Opening (34) can be used as an alignment mark to align front side processing to backside and vice versa. Trench structures can also be use to form a microstructure (41,61) for a sensor (40,60).
TL;DR: In this article, the axial temperature gradient at the solid/liquid interface for each crystal diameter/heat shield combination was calculated, and it was shown that the critical pull rate is proportional to this axial gradient, which, in turn, is a function of the crystal diameter and heat shield.
TL;DR: In this paper, LiNbO3:In (5 mol) was found to have a similar high resistance to photorefraction as LiNiobate:Zn (7.5 mol), which is the most indium-doped lithium niobate crystal.
Abstract: Highly indium‐doped lithium niobate crystals have been grown. It was found that a LiNbO3:In (5 mol %) crystal had a similar high resistance to photorefraction as a LiNbO3:Zn (7.5 mol %) crystal. The result of x‐ray fluorescence showed that the doped concentration of In in LiNbO3:In (5 mol % in the melt) exceeds the concentration threshold of trivalant elements (3.0 mol % in the crystal). The LiNbO3:In (5 mol %) crystal is another doped LiNbO3 crystal with high resistance to light‐induced refractive index damage.
TL;DR: In this article, an ice film with thickness greater than 10 A was crystallized on a clean Pt(111) surface, and its external surface structure was investigated at 90 K by dynamical low-energy electron diffraction (LEED), followed by molecular dynamics simulations and ab initio quantum chemical calculations.
Abstract: An ice film with thickness greater than 10 A was crystallized on a clean Pt(111) surface. Its external surface structure was investigated at 90 K by dynamical low-energy electron diffraction (LEED), followed by molecular dynamics simulations and ab initio quantum chemical calculations. The results favor the common hexagonal ice 1h structure over other forms of ice, with (0001) termination. A full-bilayer termination is found, but with much enhanced amplitudes of motion of the O atoms in the outermost layer of H{sub 2}O molecules, even at 90 K, so that these molecules were undetected experimentally by LEED. 14 refs., 2 figs.
TL;DR: For the first time, virus crystal growth dynamics and morphology have been investigated in real time on the nanometer scale and mechanisms for defect incorporation and suggest factors that limit growth rate and uniformity are suggested.
Abstract: For the first time, virus crystal growth dynamics and morphology have been investigated in real time on the nanometer scale. Individual monomers on the (111) face of cubic satellite tobacco mosaic virus (STMV) crystals were resolved and used to determine crystal packing. Growth of STMV proceeded by two- and three-dimensional nucleation to formed ``stacks'' of islands. No dislocations were observed. Small islands provided an estimate of critical radius size and the free energy of the step edge, \ensuremath{\alpha}. Step advancement rates were used to determinate the kinetic coefficient \ensuremath{\beta}. Images illustrate mechanisms for defect incorporation and suggest factors that limit growth rate and uniformity.
TL;DR: In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K as discussed by the authors.
Abstract: In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K. The hardness of all three materials increases by a factor of ∼2.5 on cooling to liquid nitrogen temperature. High-magnification SEM photographs revealed that the deformation and cracking patterns of the glasses changed strikingly: no shear lines were observed within the indentations, and ring cracking occurred instead of radial/median cracking. In addition, cracking occurs at much higher loads than at room temperature. The hardness results have been explained in terms of volume flow (densification) rather than shear flow (viscous or plastic) for the glasses at low temperature. The quartz crystal, on the other hand, deformed plastically at both room temperature and 77 K. Cracking differences result from changes in both flow and water activity
TL;DR: In this article, the density and distribution of inclusions of the excess component in CdTe and (Cd,Zn)Te crystals grown by the Bridgman method and by the travelling heater method (THM) have been investigated by transmission infrared (IR) microscopy.
IBM1
TL;DR: In this paper, the authors show that the high impurity density near the surface can be frozen in as the crystal grows, permitting the growth of highly supersaturated solid solutions in semiconductors.
Abstract: Any defect or impurity has some inherent stress, so near a free surface its energy is reduced by relief of this stress. The defect stress also couples to the intrinsic surface stress. In general, the result is to enhance impurity solubility and diffusion near the surface. With certain assumptions regarding the kinetics, the high impurity density near the surface can be frozen in as the crystal grows, permitting the growth of highly supersaturated solid solutions, e.g., high dopant concentrations in semiconductors. Calculations for carbon near the Si(001) surface illustrate the solubility enhancement.
TL;DR: In this paper, the authors showed that a double-oriented film of practically unlimited size can be obtained from a uniaxially drawn film of P(VDF/TrFE) by crystallization in the paraelectric phase with its surfaces free from any constraint other than tensile stress along the chain axis.
Abstract: We find that a highly double‐oriented film of practically unlimited size can be obtained from a uniaxially drawn film of P(VDF/TrFE) by crystallization in the paraelectric phase with its surfaces free from any constraint other than tensile stress along the chain axis. The c axis (the chain axis) and the [110] axis in the orthorhombic system of the poled crystalline film are parallel to the stretching axis and perpendicular to the film plane, respectively. Contrary to conventional crystalline polymer films, the present film has no amorphous region and no lamellar crystal. The film exhibits highly anisotropic characteristics in optical, mechanical, and piezoelectric properties.
TL;DR: It was concluded that the decrease in the effective interfacial energy of the embryo due to the coalescence produced an enhancement of the crystal nucleation, and that the enhancement mechanism must have played an essential role for the macroscopically observable crystallization below 250 K.
Abstract: A homogeneous-nucleation-based crystallization was found in o-terphenyl in the glass-transition temperature region with an adiabatic calorimeter, and the crystallization process was investigated by direct microscopic observation. The crystallization showed its maximum rate at 248 and ceased at 250 K, while the ordinary crystal-growth process was observed to proceed only above 255 K. The two crystals formed at 248 and 297 K showed the same x-ray-diffraction patterns, indicating that they were in the same crystalline phase. The nucleation-based crystallization was observed in the temperature range of 225 to 250 K as advance of the crystal front into the liquid phase under the microscope, and the crystalline phase exhibited the appearance of the aggregation of fine crystallites which was consistent with the presence of residual entropy and the premelting property. From these results, the crystallization process was interpreted to proceed through the coalescence of crystal embryos into the crystalline phase on the liquid-crystal interface. It was concluded that the decrease in the effective interfacial energy of the embryo due to the coalescence produced an enhancement of the crystal nucleation, and that the enhancement mechanism must have played an essential role for the macroscopically observable crystallization below 250 K.
TL;DR: Using streptavidin as a model system, it is firmly established that 3D crystal growth from 2D crystals on lipid layers occurs by epitaxy, and that lipid layers alone are equally effective at promoting epitaxial crystal growth.
Patent•
06 Jun 1995TL;DR: In this paper, a diamond electronic device constituted of a diamond crystal formed on a substrate is described, where the diamond crystal serves as a heat-radiating layer and a semiconductor layer and an electrode layer are provided on the crystal.
Abstract: A diamond electronic device constituted of a diamond crystal formed on a substrate comprises a diamond crystal having the ratio (h/L) of length (h) of the diamond crystal in direction substantially perpendicular to the face of the substrate to length (L) of the diamond crystal in direction parallel to the face of the substrate ranging from 1/4 to 1/1000 and an upper face of the diamond crystal making an angle of from substantially 0° to 10° to the face of the substrate, and a semiconductor layer and an electrode layer provided on the diamond crystal, wherein the diamond crystal serves as a heat-radiating layer.
TL;DR: In this article, powder neutron diffraction was used to determine the underlying antiferromagnetic component of the structure of the M"O6 octahedra and showed that they are weakly ferromagnetic.
Abstract: N&MI1P04*H20 (MI1 = Mn, Fe, Co, Ni) and KM"PO4qH20 (MI1 = Mn, Co, Ni) have been prepared and characterized by X-ray powder diffraction and bulk magnetometry, and the corresponding deuterio compounds, by neutron powder diffraction. They are isomorphous (space group Pmn21). The divalent metal ions form approximately square-planar layers of comer-sharing octahedra, the layers being bound by hydrogen bonds in the ammonium compounds and by electrostatic interactions in the potassium ones. In all cases, the M"O6 octahedra are severely distorted, the point symmetry being C2". Bulk susceptibility measurements on NH4FeP04eH20, N&MnP04aH20, and KMnP04*H2O show they are weakly ferromagnetic, with Nee1 temperatures of TN = 24.0(2), 17.5(3), and 18.0(3) K, respectively. Powder neutron diffraction was used to determine the underlying antiferromagnetic component of the structures. All three materials have simple two-sublattice structures, with the antiferromagnetic moments along &[OlO], perpendicular to the plane of the metal-containing layers. Analysis using the irreducible representations of the space group shows that the ferromagnetic moments are parallel to [OOl].