A simple hydrothermal method has been developed for the systematic synthesis of lanthanide orthophosphate crystals with different crystalline phases and morphologies. It has been shown that pure LnPO4 compounds change structure with decreasing Ln ionic radius:  i.e., the orthophosphates from Ho to Lu as well as Y exist only in the tetragonal zircon (xenotime) structure, while the orthophosphates from La to Dy exist in the hexagonal structure under hydrothermal treatment. The obtained hexagonal structured lanthanide orthophosphate LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) products have a wirelike morphology. In contrast, tetragonal LnPO4 (Ln = Ho, Er, Tm, Yb, Lu, Y) samples prepared under the same experimental conditions consist of nanoparticles. The obtained hexagonal LnPO4 (Ln = La → Tb) can convert to the monoclinic monazite structured products, and their morphologies remained the same after calcination at 900 °C in air (Hexagonal DyPO4 is an exceptional case, it transformed to tetragonal DyPO...

Systematic synthesis and characterization of single-crystal lanthanide orthophosphate nanowires.

Rare earth phosphates have recently been investigated as a potential ceramic material in view of their high-temperature phase stability, high melting point, low thermal conductivity, optical, fluor...

High-Surface-Area Nanocrystalline Cerium Phosphate through Aqueous Sol−Gel Route

Here, we describe the fast and mass fabrication of monazite lanthanum orthophosphate (LaPO4) nanoparticles via a simple sol−gel method under the assistance of microwave irradiation. The procedure involves formation of homogeneous, transparent, metal−citrate−EDTA gel precursors using both citric acid (CA) and ethylenediamine tetraacetic acid (EDTA) as the complexing agent followed by microwave irradiation, which promotes prompt thermal decomposition of the metal−citrate−EDTA gel precursors to yield the final nanoparticles. Thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the as-synthesized nanoparticles. About 23 g of single monoclinic phase, approximately 100 nm diameter, LaPO4 spherical nanoparticles were readily obtained at 800 °C within 0.5 h, and the nanospheres were themselves composed of Ultrafine nano...

Microwave-Assisted Sol−Gel Synthesis and Photoluminescence Characterization of LaPO4:Eu3+,Li+ Nanophosphors

Synthesis of rod-shaped nanocrystalline lanthanum phosphate with an average length of 40 nm even after calcination at 400 °C has been realized through a room-temperature aqueous sol-gel process. The sol is characterized by particle-size, zeta-potential, and viscosity measurements. Gelation of the sol is induced by ammonia. The lanthanum phosphate phase-formation process is followed by thermal, Fourier-transform IR, and X-ray diffraction analysis. Transmission electron microscopy shows that the sol and gel particles have a rod-shaped morphology and comparable particle sizes. Using the Scherrer equation a crystallite size of 11 nm is obtained for the gel powder calcined at 400°C and Brunauer-Emmett-Teller (BET) nitrogen-adsorption analysis showed a high specific surface area of 100 m 2 g -1 . Ammonia temperature-programmed desorption measurements show that the density of Lewis acid sites is four times higher than ever reported in the case of lanthanum phosphates. The catalytic activity of the above sample is demonstrated by using it as a Lewis-acid catalyst in an acetal-formation reaction with a very good yield of 85 %. The sol is used to develop nanocoatings on a glass surface and the morphology of the coatings is investigated using atomic force microscopy and scanning electron microscopy. The microstructure of the coating confirmed the rod-shaped nature of the sol particles. The coating was uniform with a thickness of about 55 nm.

A Facile Sol–Gel Strategy for the Synthesis of Rod‐Shaped Nanocrystalline High‐Surface‐Area Lanthanum Phosphate Powders and Nanocoatings

The first alkaline-earth metal tin(II) phosphate, BaSn2 (PO4 )2 , has been discovered, which consists of layered structures constructed from strictly alternating [SnO3 ]4- and [PO4 ]3- moieties. This compound is expected to have a large birefringence with Δn≈0.071 at 1064 nm, owing to the presence of stereochemically active lone pair metal cations.

Lone-Pair Enhanced Birefringence in an Alkaline-Earth Metal Tin(II) Phosphate BaSn2 (PO4 )2.

Various rare earth phosphates [rare earth elements: R = La, Ce, Pr, Nd, Sm, Yb, and Y; phosphates: Monazite-type, Xenotime-type, Rhabdophane-type, and Weinshenkite-type orthophosphates RPO4, polyphosphate R(PO3)3, and ultraphosphate RP5O14] were synthesized by heating the mixtures of each rare earth oxide and diammonium hydrogenphosphate or phosphoric acid. The compositions of rare earth phosphates were determined by XRD, FT-IR, and TG–DTA. Catalytic properties were studied as one of properties of various rare earth phosphates. Specific surface areas of samples were measured by the BET method. Acid strengths and amounts of acidic sites were measured using several indicators by n-butylamine titration. Acidic properties were also confirmed by adsorption of ammonia. Various rare earth phosphates were characterized by catalytic activities on dehydration reaction of 2-propanol, cracking/dehydrogenation
reaction of cumene, and isomerization reaction of butene. The characterization of catalysts was discussed with regard to type of rare earth elements, type of phosphates, and type of phosphorus resources.

Ai Moriwaki

Papers

Formation and catalytic characterization of various rare earth phosphates