Pressure-induced phase transitions of piezoelectric single crystals from the langasite family: La~3~Nb~0.5~Ga~5.5~O~14~ and La~3~Ta~0.5~Ga~5.5~O~14~
Pavlovska, A.; Werner, S.; Maximov, B.; Mill, B.; Acta Crystallographica Section B 58 (2002) 939–947; doi:10.1107/S0108768102010273

data_2103521
_publ_section_title
;
 Pressure-induced phase transitions of piezoelectric single crystals
 from the langasite family: La~3~Nb~0.5~Ga~5.5~O~14~ and
 La~3~Ta~0.5~Ga~5.5~O~14~
;
_journal_issue                   6
_journal_name_full               'Acta Crystallographica Section B'
_journal_page_first              939
_journal_page_last               947
_journal_paper_doi               10.1107/S0108768102010273
_journal_volume                  58
_journal_year                    2002
_chemical_formula_sum            'Ga5.5 La3 Nb0.5 O14'
_chemical_formula_weight         1070.65
_space_group_IT_number           150
_symmetry_space_group_name_Hall  'P 3 2"'
_symmetry_space_group_name_H-M   'P 3 2 1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method           SHELXL-97
_cell_angle_alpha                90.00
_cell_angle_beta                 90.00
_cell_angle_gamma                120.00
_cell_formula_units_Z            1
_cell_length_a                   7.783
_cell_length_b                   7.783
_cell_length_c                   4.994
_cell_measurement_temperature    293(2)
_cell_volume                     262.0
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 1990)'
_diffrn_ambient_pressure         18.5E+6
_diffrn_ambient_temperature      293(2)
_diffrn_measured_fraction_theta_full 0.238
_diffrn_measured_fraction_theta_max 0.238
_diffrn_radiation_source         synchrotron
_diffrn_radiation_wavelength     0.54920
_diffrn_reflns_av_R_equivalents  0.0000
_diffrn_reflns_av_sigmaI/netI    0.0649
_diffrn_reflns_limit_h_max       10
_diffrn_reflns_limit_h_min       -12
_diffrn_reflns_limit_k_max       8
_diffrn_reflns_limit_k_min       -9
_diffrn_reflns_limit_l_max       8
_diffrn_reflns_limit_l_min       -6
_diffrn_reflns_number            305
_diffrn_reflns_theta_full        32.88
_diffrn_reflns_theta_max         32.88
_diffrn_reflns_theta_min         3.15
_exptl_absorpt_coefficient_mu    15.407
_exptl_crystal_density_diffrn    6.786
_exptl_crystal_density_method    'not measured'
_exptl_crystal_F_000             474
_refine_diff_density_max         2.573
_refine_diff_density_min         -1.939
_refine_diff_density_rms         0.606
_refine_ls_abs_structure_details 'Flack H D (1983), Acta Cryst. A39, 876-881'
_refine_ls_abs_structure_Flack   -0.1(3)
_refine_ls_extinction_coef       0.011(13)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     SHELXL
_refine_ls_goodness_of_fit_ref   1.775
_refine_ls_hydrogen_treatment    mixed
_refine_ls_matrix_type           full
_refine_ls_number_parameters     28
_refine_ls_number_reflns         305
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.775
_refine_ls_R_factor_all          0.0938
_refine_ls_R_factor_gt           0.0901
_refine_ls_shift/su_max          0.000
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.1000P)^2^+0.0000P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.2385
_refine_ls_wR_factor_ref         0.2405
_reflns_number_gt                286
_reflns_number_total             305
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            sn0021-18.5d3.cif
_cod_data_source_block           18.5d3
_cod_depositor_comments
;
 Correcting the reference to the optimal entry by changing it from
 '2103521' to '2103520'. The reference now correctly refers to the
 entry with the lowest _refine_ls_R_factor_all value.

 Antanas Vaitkus,
 2018-11-16

The _diffrn_ambient_pressure was taken from the original data block
header, after comparison with the paper text and supplementary
material.

When more than one structure was present in the sn0021.cif file for a
given pressure, the structure with the minimal _refine_ls_R_factor_all
value was taken as the best one, and all others marked with the
'_cod_suboptimal_structure yes' tag.

Changing (with the help of Perl) all _diffrn_radiation_source values in
the files that were reportedly colected on the HASYLAB D3 beamline
(Hamburg) from 'fine-focus sealed tube' to synchrotron.

The command was:

perl -i -ne \
    "s/'fine-focus sealed tube'/synchrotron/; \
    print unless /_diffrn_radiation_type|_diffrn_radiation_monochromator/" \
    *d3*.cif \
    11.57split.cif \
    21.85split.cif \
    22.85split.cif

Saulius Gra\<zulis

 Removed the _cod_suboptimal_structure data item in preparation for
 its deprecation. The fact that the structure is a suboptimal one
 should be derived from the presence of the _cod_related_optimal_struct
 data item.

 Antanas Vaitkus,
 2019-05-21
;
_cod_original_formula_sum        'Ga5.50 La3 Nb0.50 O14'
_cod_related_optimal_struct      2103520
_cod_database_code               2103521