data_1517726
_publ_section_title
;
 Phase transition and negative thermal expansion in tetragonal Nb O P O4
;
_journal_name_full               'Journal of Solid State Chemistry'
_journal_page_first              303
_journal_page_last               307
_journal_volume                  141
_journal_year                    1998
_chemical_formula_structural     'Nb O (P O4)'
_chemical_formula_sum            'Nb O5 P'
_chemical_name_systematic        'Niobium Oxide Phosphate(V) - Ht'
_space_group_IT_number           129
_symmetry_Int_Tables_number      129
_symmetry_space_group_name_Hall  '-P 4a 2a'
_symmetry_space_group_name_H-M   'P 4/n m m :2'
_cell_angle_alpha                90.
_cell_angle_beta                 90.
_cell_angle_gamma                90.
_cell_formula_units_Z            2
_cell_length_a                   6.4043
_cell_length_b                   6.4043
_cell_length_c                   4.1217
_cell_volume                     169.052
_diffrn_ambient_temperature      498.15
_[local]_cod_data_source_file    NbPO5_P4_nmm_DC271.cif
_[local]_cod_data_source_block   chateigner
_[local]_cod_cif_authors_sg_H-M  'P 4/n m m Z'
_[local]_cod_chemical_formula_sum_orig 'Nb1 O5 P1'
_cod_original_cell_volume        169.05
_cod_database_code               1517726
loop_
_symmetry_equiv_pos_site_id
_symmetry_equiv_pos_as_xyz
1 'y+1/2, x+1/2, -z'
2 '-y, x+1/2, -z'
3 'y+1/2, -x, -z'
4 '-y, -x, -z'
5 'x+1/2, y+1/2, -z'
6 '-x, y+1/2, -z'
7 'x+1/2, -y, -z'
8 '-x, -y, -z'
9 '-y+1/2, -x+1/2, z'
10 'y, -x+1/2, z'
11 '-y+1/2, x, z'
12 'y, x, z'
13 '-x+1/2, -y+1/2, z'
14 'x, -y+1/2, z'
15 '-x+1/2, y, z'
16 'x, y, z'
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_symmetry_multiplicity
_atom_site_Wyckoff_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_occupancy
_atom_site_B_iso_or_equiv
Nb1 Nb5+ 2 c 0.25 0.25 0.7813(3) 1. 0
O1 O2- 2 c 0.25 0.25 0.2049(4) 1. 0
P2 P5+ 2 b 0.25 0.75 0.5 1. 0
O2 O2- 8 i 0.75 0.4444(1) 0.2875(2) 1. 0
loop_
_atom_type_symbol
_atom_type_oxidation_number
Nb5+ 5
O2- -2
P5+ 5
