Solid State lonics 63-65 ( 1993) 50!-505 North-Holland SOLID STATE IONICS Reaction of niobium phosphate with hydrazine: structural modification M. Cantero, M. Martinez-Lara, S. Bruque and L. Moreno-Real Departamento de Qulmicalnorg&nica,Cristalografiay Mineralogla, Universidad de Mdtlaga,Apdo. 59, 29071-Mdlaga,Spain The reaction between hydrazine and NbOPO4"nH20 (n < 3) gives an amorphous solid with a high thermal and hydrolitic stability. The presenceof hydrazine in the solid has been detectedby several bands in the IR spectrumbetween 1500-1550cm- J and 3300-3400 cm-~. The solid maintains its amorphous nature after the elimination of hydrazine at 600°C, and below the crystallization temperature (800 °C) we have an amorphousniobiumphosphatefree of hydrazinepossibly with catalyticproperties. I. Introduction The phosphates of the family MO(XO4)'nH20 (M = V, Nb, Ta; X = P, As) are layered isostructural compounds, and X-ray diffraction studies have sta- blished the structures of tetragonal form [ 1 ]. In its tetragonal form, the structure consist of chains of corner-shared [MO6] octahedra running parallel to the c axis. In the ab plane, each [MO6] octahedra shares corners with four [XOa] tetrahedra, which link the octahedral chains to produce a three-dimen- sional lattice. The hydrated niobium phosphate, NbOPO4.nHzO (n<3) (NbP), is a layered host compound with [NbO (H20) PO4 ] layers, and their formation may be explained by breaking of the long M-O linkages of the anhydrous form and subse- quent substitution of the O of the adjacent layer by a water molecule. It intercalates different types of guest molecules, in particular different types of amines, phosphoric acid and sulphuric acid [2]. The aim of this work is to obtain a niobium phos- phate with high surface activity avoiding the pres- ence of alkaline ions (Na ÷, K ÷ ) in the solid, which are retained when conventional routes of synthesis are used [3,4]. Martins has used and amorphous ni- obium phosphate contaminated with potassium and has studied its texture, surface acidic and catalytic properties [3 ]. Elsevier SciencePublishers B.V. 2. Experimental 2.1. Preparation of the compound The synthesis of NbP has been made by the method of Chernorukov [ 5,6 ] and modified by Bruque [ 6 ]. 20 g of Nb205 were dissolved in a mixture of 140 ml of HF (45%) and 15 ml of HNO3 (60%), then 82 ml of H3PO4 (85%) were added. This solution was heated in a water bath until a white crystalline solid appeared, that was separated by decantation, and latter was put in 560 ml ofHNO3 5 M. The suspen- sion was centrifuged, and the separated solid was washed with bidistilled water several times, then dried in oven at 50°C and finally stored in 76% rel- ative humidity environment. The reaction between 50 ml of pure hydrazine and 1 g of NbP at room temperature was stirred for one day. The resulting white suspension was separated by centrifugation, and the solid was washed with bi- distilled water several times, dried in oven at 50°C and stored in 58% relative humidity environment. 2.2. Characterization of the product The niobium was determined gravimetrically by dissolving the specimen in hydrofluoric acid, precip- itating the niobium with cupferron and roasting to Nb205 [ 8 ]. Phosphorus was determined colorimet- rically as molybdophosphate complex [ 9 ]. The N2H4