data_Modulated structure of Sr2Nb2O7
_cell_length_a                                               3.9537(6)      
_cell_length_b                                               26.749(4)      
_cell_length_c                                               5.7002(10)     
_cell_angle_alpha                                            90             
_cell_angle_beta                                             90             
_cell_angle_gamma                                            90             
_cell_volume                                                 614.71(17)     
_cell_measurement_pressure                                   ?              
_cell_measurement_radiation                                  ?              
_cell_measurement_reflns_used                                ?              
_cell_measurement_temperature                                ?              
_cell_measurement_theta_max                                  ?              
_cell_measurement_theta_min                                  ?              
_cell_measurement_wavelength                                 ?              
_cell_modulation_dimension                                   1              
loop_
_cell_wave_vector_seq_id                                    
_cell_wave_vector_x                                         
_cell_wave_vector_y                                         
_cell_wave_vector_z                                         
1   0.48800   0.00000   0.00000
_cell_formula_units_Z                                        4
_symmetry_cell_setting                                       orthorhombic
_symmetry_ssg_name_IT                                        Cmc21(\a00)0s
loop_
_symmetry_ssg_equiv_pos_seq_id                              
_symmetry_ssg_equiv_pos_as_xyz                              
1   x1,x2,x3,x4
2   x1,-x2,1/2+x3,1/2+x4
3   -x1,-x2,1/2+x3,-x4
4   -x1,x2,x3,1/2-x4
5   1/2+x1,1/2+x2,x3,x4
6   1/2+x1,1/2-x2,1/2+x3,1/2+x4
7   1/2-x1,1/2-x2,1/2+x3,-x4
8   1/2-x1,1/2+x2,x3,1/2-x4
loop_
_atom_type_symbol                                           
_atom_type_oxidation_number                                 
_atom_type_number_in_cell                                   
_atom_type_scat_dispersion_real                             
_atom_type_scat_dispersion_imag                             
_atom_type_scat_source                                      
_atom_type_scat_Cromer_Mann_a1                              
_atom_type_scat_Cromer_Mann_b1                              
_atom_type_scat_Cromer_Mann_a2                              
_atom_type_scat_Cromer_Mann_b2                              
_atom_type_scat_Cromer_Mann_a3                              
_atom_type_scat_Cromer_Mann_b3                              
_atom_type_scat_Cromer_Mann_a4                              
_atom_type_scat_Cromer_Mann_b4                              
_atom_type_scat_Cromer_Mann_c                               
Sr 0  16  -0.117   2.203 International_Tables_Vol_C
17.566299 1.5564 9.8184 14.0988 5.422 0.1664 2.6694 132.376007 2.5064           
Nb 0  16  -0.828   2.840 International_Tables_Vol_C
17.614201 1.18865 12.0144 11.766 4.04183 0.204785 3.53346 69.7957 3.75591       
O  0  56   0.006   0.004 International_Tables_Vol_C
3.0485 13.2771 2.2868 5.7011 1.5463 0.3239 0.867 32.908901 0.2508               
_chemical_formula_sum                                        'Sr2 Nb2 O7'
_chemical_formula_weight                                     473            
_exptl_crystal_colour                                        ?              
_exptl_crystal_description                                   ?              
_exptl_crystal_size_max                                      ?              
_exptl_crystal_size_mid                                      ?              
_exptl_crystal_size_min                                      ?              
_exptl_crystal_size_rad                                      ?              
_exptl_crystal_density_diffrn                                5.11           
_exptl_crystal_density_meas                                  ?              
_exptl_crystal_density_meas_temp                             ?              
_exptl_crystal_density_method                                ?              
_exptl_crystal_F_000                                         856            
_exptl_absorpt_correction_type                               none
_exptl_absorpt_coefficient_mu                                ?
_exptl_absorpt_correction_T_min                              1.000
_exptl_absorpt_correction_T_max                              1.000
_diffrn_measurement_device                                   'imaging plate system'
_diffrn_measurement_device_type                              'IPDS Stoe'
_diffrn_measurement_method                                   '??integration method??'
_diffrn_radiation_probe                                      'X-ray'
_diffrn_radiation_type                                       ?
_diffrn_radiation_wavelength                                 0.5
_diffrn_standards_number                                     ?              
_diffrn_standards_decay_%                                    ?              
_diffrn_standards_interval_count                             ?              
_diffrn_standards_interval_time                              ?              
_diffrn_reflns_limit_h_min                                   -9             
_diffrn_reflns_limit_h_max                                   8              
_diffrn_reflns_limit_k_min                                   -64            
_diffrn_reflns_limit_k_max                                   62             
_diffrn_reflns_limit_l_min                                   -13            
_diffrn_reflns_limit_l_max                                   8              
_diffrn_reflns_limit_index_m_1_min                           -1             
_diffrn_reflns_limit_index_m_1_max                           1              
_reflns_limit_h_min                                          0              
_reflns_limit_h_max                                          9              
_reflns_limit_k_min                                          0              
_reflns_limit_k_max                                          64             
_reflns_limit_l_min                                          -13            
_reflns_limit_l_max                                          8              
_reflns_limit_index_m_1_min                                  -1             
_reflns_limit_index_m_1_max                                  1              
_diffrn_reflns_number                                        18977          
_diffrn_reflns_theta_min                                     1.07           
_diffrn_reflns_theta_max                                     37.61          
_diffrn_reflns_av_R_equivalents                              0.0742         
_diffrn_reflns_av_sigmaI/netI                                0.0075         
_reflns_observed_criterion                                   3              
_reflns_number_total                                         5126           
_reflns_number_observed                                      4888           
_refine_ls_structure_factor_coef                             F              
_refine_ls_weighting_scheme                                  sigma          
_refine_ls_weighting_details                                 'w=1/(σ²(F)+0.0004F²)'
_refine_ls_R_factor_gt                                       0.0565         
_refine_ls_wR_factor_gt                                      0.0824         
_refine_ls_R_factor_all                                      0.0594         
_refine_ls_wR_factor_ref                                     0.0842         
_refine_ls_number_reflns                                     5126           
_refine_ls_number_parameters                                 105            
_refine_ls_goodness_of_fit_ref                               3.26           
_refine_ls_goodness_of_fit_obs                               3.26           
_refine_ls_shift/su_max                                      0.0005         
_refine_ls_shift/su_mean                                     0.0000         
_refine_diff_density_max                                     ?              
_refine_diff_density_min                                     ?              
_refine_ls_extinction_method                                 'none'
_refine_ls_extinction_coef                                   ?
loop_
_atom_site_label                                            
_atom_site_type_symbol                                      
_atom_site_fract_x                                          
_atom_site_fract_y                                          
_atom_site_fract_z                                          
_atom_site_U_iso_or_equiv                                   
_atom_site_symmetry_multiplicity                            
_atom_site_occupancy                                        
Sr1 Sr  0.5          0.20587(2)   0.02976(16)   0.01184(12)   4 1
Sr2 Sr  0.5          0.051848(15) 0.46660(13)   0.00606(7)    4 1
Nb1 Nb  0            0.162003(12) 0.5           0.00324(5)    4 1
Nb2 Nb  0.5          0.442230(11) 0.47044(9)    0.00229(5)    4 1
O1  O   0            0.00700(14)  0.2221(8)     0.0083(8)     4 1
O2  O   0            0.10988(18)  0.1772(11)    0.0144(12)    4 1
O3  O   0.5          0.15090(15)  0.4728(10)    0.0107(10)    4 1
O4  O   0            0.21408(16)  0.2857(9)     0.0080(7)     4 1
O5  O   0.5          0.30052(19)  0.2640(10)    0.0105(9)     4 1
O6  O   0.5          0.40684(14)  0.1710(8)     0.0078(6)     4 1
O7  O   0            0.45098(16)  0.4511(11)    0.0092(8)     4 1
loop_
_atom_site_aniso_label                                      
_atom_site_aniso_type_symbol                                
_atom_site_adp_type                                         
_atom_site_aniso_U_11                                       
_atom_site_aniso_U_22                                       
_atom_site_aniso_U_33                                       
_atom_site_aniso_U_12                                       
_atom_site_aniso_U_13                                       
_atom_site_aniso_U_23                                       
Sr1 Sr Uani  0.00386(11)   0.0221(2)     0.0090(2)     0
             0             0.0054(2)
Sr2 Sr Uani  0.00394(10)   0.00764(11)   0.00637(15)   0
             0            -0.00139(12)
Nb1 Nb Uani  0.00206(8)    0.00394(8)    0.00359(11)   0
             0             0.00035(7)
Nb2 Nb Uani  0.00125(8)    0.00352(7)    0.00199(10)   0
             0            -0.00014(7)
O1  O  Uani  0.0113(17)    0.0059(10)    0.0073(14)    0
             0             0.0024(9)
O2  O  Uani  0.025(3)      0.0083(12)    0.0096(16)    0
             0            -0.0026(13)
O3  O  Uani  0.0021(7)     0.0097(10)    0.020(2)      0
             0            -0.0011(16)
O4  O  Uani  0.0082(12)    0.0079(11)    0.0074(12)    0
             0             0.0038(10)
O5  O  Uani  0.0111(17)    0.0103(12)    0.0097(15)    0
             0             0.0036(11)
O6  O  Uani  0.0098(13)    0.0073(9)     0.0059(11)    0
             0            -0.0019(9)
O7  O  Uani  0.0022(8)     0.0116(11)    0.014(2)      0
             0             0.0009(14)
loop_
_atom_site_Fourier_wave_vector_seq_id                       
_atom_site_Fourier_wave_vector_x                            
_atom_site_Fourier_wave_vector_y                            
_atom_site_Fourier_wave_vector_z                            
1  0.48800  0.00000  0.00000
loop_
_atom_site_displace_Fourier_atom_site_label                 
_atom_site_displace_Fourier_axis                            
_atom_site_displace_Fourier_wave_vector_seq_id              
_atom_site_displace_Fourier_cos                             
_atom_site_displace_Fourier_sin                             
Sr1   x  1     0.0029(2)   0
Sr1   y  1     0           0.00473(3)
Sr1   z  1     0           0.01599(12)
Sr2   x  1     0.00021(18) 0
Sr2   y  1     0          -0.00181(2)
Sr2   z  1     0          -0.00090(12)
Nb1   x  1     0.00298(16) 0
Nb1   y  1     0           0.00050(2)
Nb1   z  1     0           0.00067(11)
Nb2   x  1     0.00398(16) 0
Nb2   y  1     0           0.00037(2)
Nb2   z  1     0           0.00047(11)
O1    x  1    -0.0289(17)  0
O1    y  1     0           0.0004(2)
O1    z  1     0           0.0003(9)
O2    x  1    -0.0471(19)  0
O2    y  1     0           0.0005(2)
O2    z  1     0           0.0003(11)
O3    x  1    -0.0001(14)  0
O3    y  1     0          -0.0006(2)
O3    z  1     0          -0.0318(13)
O4    x  1    -0.0170(15)  0
O4    y  1     0           0.0018(2)
O4    z  1     0           0.0024(12)
O5    x  1    -0.0248(16)  0
O5    y  1     0          -0.0014(2)
O5    z  1     0          -0.0031(12)
O6    x  1    -0.0166(15)  0
O6    y  1     0           0.0000(2)
O6    z  1     0           0.0015(9)
O7    x  1     0.0036(15)  0
O7    y  1     0           0.0016(2)
O7    z  1     0          -0.0293(12)
loop_
_atom_site_U_Fourier_atom_site_label                        
_atom_site_U_Fourier_tens_elem                              
_atom_site_U_Fourier_wave_vector_seq_id                     
_atom_site_U_Fourier_cos                                    
_atom_site_U_Fourier_sin                                    
Sr1   U11  1     0           0.0005(3)
Sr1   U22  1     0          -0.0150(3)
Sr1   U33  1     0          -0.0050(4)
Sr1   U12  1     0.0006(2)   0
Sr1   U13  1    -0.0001(2)   0
Sr1   U23  1     0          -0.0066(3)
