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(KxNa1-x)NbO3 ceramics modified with Li+ and Ta5+ have been produced using the mixed-oxide synthesis method. Synchrotron X-ray diffraction measurements were made on the samples from 12 K to temperatures above their ferroelectric-paraelectric transition points with 10 K measurement steps. Rietveld refinement was used to refine the patterns. Depending on the composition and temperature, rhombohedral phases, orthorhombic phases, tetragonal phases, cubic phases and two-phase mixtures were obtained. Space groups R3c (161), Amm2 (38), P4mm (99) and Pm{\overline 3}m (221) and their combinations were used to refine the rhombohedral, orthorhombic, tetragonal, cubic and mixed phases, respectively. Li+ addition suppressed the formation of the rhombohedral low-temperature phase and increased the Curie temperature. This is attributed to the size difference in ionic radii of the A-site elements, which leads to increased atomic polarizability and increased interaction with the B-site element. Li+ and Ta5+ co-doping led to a wide temperature range of coexistence between the orthorhombic and tetragonal phases. Electrical characterizations by dielectric and hysteresis measurements were used to compare with the results from the structural studies.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup1.cif
Contains datablocks global, KNN-L_12K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-L_12Ksup2.rtv
Contains datablock KNN-L_12K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup3.cif
Contains datablocks global, KNN-L_373K, Tetragonal

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-L_373Ksup4.rtv
Contains datablock KNN-L_373K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup5.cif
Contains datablocks global, KNN-L_393K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-L_393Ksup6.rtv
Contains datablock KNN-L_393K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup7.cif
Contains datablocks global, KNN-L_753K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-L_753Ksup8.rtv
Contains datablock KNN-L_753K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup9.cif
Contains datablocks global, KNN-T_12K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-T_12Ksup10.rtv
Contains datablock KNN-T_12K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup11.cif
Contains datablocks global, KNN-T_170K, orthorhombic

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-T_170Ksup12.rtv
Contains datablock KNN-T_170K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup13.cif
Contains datablocks global, KNN-T_190K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-T_190Ksup14.rtv
Contains datablock KNN-T_190K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup15.cif
Contains datablocks global, KNN-T_443K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-T_443Ksup16.rtv
Contains datablock KNN-T_443K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup17.cif
Contains datablocks global, KNN-T_643K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-T_643Ksup18.rtv
Contains datablock KNN-T_643K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup19.cif
Contains datablocks global, KNN-LT_12K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-LT_12Ksup20.rtv
Contains datablock KNN-LT_12K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup21.cif
Contains datablocks global, KNN-LT_293K, Tetragonal

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-LT_293Ksup22.rtv
Contains datablock KNN-LT_293K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup23.cif
Contains datablocks global, KNN-LT_383K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-LT_383Ksup24.rtv
Contains datablock KNN-LT_383K

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889811027701/cg5189sup25.cif
Contains datablocks global, KNN-LT_693K

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889811027701/cg5189KNN-LT_693Ksup26.rtv
Contains datablock KNN-LT_693K

Computing details top

Program(s) used to refine structure: FULLPROF.

(KNN-L_12K) top
Crystal data top
Orthorhombic, Amm2c = 5.68307 (5) Å
Hall symbol: A 2 -2V = 125.99 (1) Å3
a = 3.93132 (3) ÅX-ray radiation
b = 5.63895 (5) Å
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 7.60916251 data points
Rwp = 10.01735 parameters
Rexp = 2.1400 restraints
RBragg = 6.752
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.500000.250000.289 (2)0.0021 (8)*
O20.000000.000000.5475 (19)0.0021 (8)*0.99998
Na0.000000.000000.000000.0056 (4)*0.50830
K0.000000.000000.000000.0056 (4)*0.46844
Li0.000000.000000.000000.0056 (4)*0.02990
Zr0.000000.000000.000000.0056 (4)*0.00020
Nb0.500000.000000.5041 (14)0.00008 (16)*0.96677
 
(KNN-L_373K) top
Crystal data top
Orthorhombic, Amm2c = 5.67707 (8) Å
Hall symbol: A 2 -2V = 126.48 (1) Å3
a = 3.94655 (4) ÅX-ray radiation
b = 5.64505 (8) Å
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 11.63513751 data points
Rwp = 14.97335 parameters
Rexp = 2.2860 restraints
RBragg = 11.820
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.500000.250000.297 (3)0.0028 (12)*
O_20.000000.000000.558 (2)0.0028 (12)*
Na0.000000.000000.000000.0110 (9)*0.49787
K0.000000.000000.000000.0110 (9)*0.43465
Li0.000000.000000.000000.0110 (9)*0.01316
Zr0.000000.000000.000000.0110 (9)*0.00458
Nb0.500000.000000.5149 (17)0.050063 (4)*0.98783
(Tetragonal) top
Crystal data top
Tetragonal, P4mmc = 4.0454 (6) Å
Hall symbol: P 4 -2V = 63.21 (1) Å3
a = 3.9528 (3) ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 11.6350 data points
Rwp = 14.97335 parameters
Rexp = 2.2860 restraints
RBragg = 50.624
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.500000.250000.290 (3)0.0028 (12)*
O_20.000000.000000.551 (2)0.0028 (12)*
Na0.000000.000000.000000.0110 (9)*
K0.000000.000000.000000.0110 (9)*0.93687
Li0.000000.000000.000000.0110 (9)*0.05980
Zr0.000000.000000.000000.0110 (9)*0.00040
Nb0.500000.000000.5103 (17)0.050063 (4)*0.96677
 
(KNN-L_393K) top
Crystal data top
Tetragonal, P4mmc = 4.03898 (4) Å
Hall symbol: P 4 -2V = 63.19 (1) Å3
a = 3.95531 (3) ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 12.54713751 data points
Rwp = 16.83830 parameters
Rexp = 2.3080 restraints
RBragg = 13.771
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.000000.500000.549 (4)0.0057 (12)*
O_20.500000.500000.050 (5)0.0057 (12)*
Na0.000000.000000.000000.0210 (8)*0.50829
K0.000000.000000.000000.0210 (8)*0.46843
Li0.000000.000000.000000.0210 (8)*0.02990
Zr0.000000.000000.000000.0210 (8)*0.00040
Nb0.500000.500000.493 (4)0.0102 (3)*0.96675
 
(KNN-L_753K) top
Crystal data top
Cubic, Pm3mV = 63.38 (1) Å3
Hall symbol: -P 4 2 3X-ray radiation
a = 3.98709 (2) Å
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 11.67413751 data points
Rwp = 14.70020 parameters
Rexp = 2.3560 restraints
RBragg = 16.931
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O0.500000.500000.000000.019105 (4)*
Na0.000000.000000.000000.0357 (7)*0.50853
K0.000000.000000.000000.0357 (7)*0.46835
Li0.000000.000000.000000.0357 (7)*0.03014
Zr0.000000.000000.000000.0357 (7)*0.00239
Nb0.500000.500000.500000.0212 (3)*0.96635
 
(KNN-T_12K) top
Crystal data top
Rhombohedral, R3cα = 90°
Hall symbol: R 3 -2"cγ = 120°
a = 5.612706 (1) ÅV = 377.42 (1) Å3
c = 13.83390 ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 6.39716251 data points
Rwp = 8.34327 parameters
Rexp = 1.9140 restraints
RBragg = 6.681
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O0.166670.333330.833330.0046 (9)*
Na0.000000.000000.0170 (8)0.0007 (4)*0.50626
K0.000000.000000.0170 (8)0.0007 (4)*0.48460
Zr0.000000.000000.0170 (8)0.0007 (4)*0.00080
Nb0.000000.000000.2630 (4)0.00025 (13)*0.87787
Ta0.000000.000000.2630 (4)0.00025 (13)*0.09794
 
(KNN-T_170K) top
Crystal data top
Rhombohedral, R3cα = 90°
Hall symbol: R 3 -2"cγ = 120°
a = 5.616620 (1) ÅV = 377.91 (1) Å3
c = 13.83255 ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 6.50416251 data points
Rwp = 8.56135 parameters
Rexp = 1.8840 restraints
RBragg = 6.376
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O0.166670.333330.833330.0021 (10)*
Na0.000000.000000.0214 (8)0.0077 (6)*0.53520
K0.000000.000000.0214 (8)0.0077 (6)*0.38601
Li0.000000.000000.0214 (8)0.0077 (6)*0.03000
Zr0.000000.000000.0214 (8)0.0077 (6)*0.00180
Nb0.000000.000000.2646 (5)0.00377 (16)*0.90000
Ta0.000000.000000.2646 (5)0.00377 (16)*0.10800
Sb0.000000.000000.2646 (5)0.00377 (16)*0.02907
(orthorhombic) top
Crystal data top
Orthorhombic, Amm2c = 5.67068 (10) Å
Hall symbol: A 2 -2V = 125.97 (1) Å3
a = 3.94036 (6) ÅX-ray radiation
b = 5.63778 (12) Å
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 6.5040 data points
Rwp = 8.56135 parameters
Rexp = 1.8840 restraints
RBragg = 8.835
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.500000.250000.3 (6)0.0021 (10)*
O20.000000.000000.6 (6)0.0021 (10)*0.99998
Na0.000000.000000.0 (6)0.0077 (6)*0.53395
K0.000000.000000.0 (6)0.0077 (6)*0.38510
Li0.000000.000000.0 (6)0.0077 (6)*0.02993
Zr0.000000.000000.0 (6)0.0077 (6)*0.00180
Nb0.500000.000000.5 (6)0.00377 (16)*0.89790
Ta0.500000.000000.5 (6)0.00377 (16)*0.10775
Sb0.500000.000000.5 (6)0.00377 (16)*0.02901
 
(KNN-T_190K) top
Crystal data top
Orthorhombic, Amm2c = 5.67081 (4) Å
Hall symbol: A 2 -2V = 126.00 (1) Å3
a = 3.94128 (2) ÅX-ray radiation
b = 5.63739 (4) Å
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 6.34116251 data points
Rwp = 8.22935 parameters
Rexp = 1.8860 restraints
RBragg = 6.828
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.500000.250000.289 (2)0.0023 (9)*
O20.000000.000000.549 (2)0.0023 (9)*
Na0.000000.000000.000000.0069 (5)*0.50663
K0.000000.000000.000000.0069 (5)*0.48676
Zr0.000000.000000.000000.0069 (5)*0.00020
Nb0.500000.000000.5079 (17)0.00188 (16)*0.87418
Ta0.500000.000000.5079 (17)0.00188 (16)*0.09934
 
(KNN-T_443K) top
Crystal data top
Tetragonal, P4mmc = 4.01987 (3) Å
Hall symbol: P 4 -2V = 63.13 (1) Å3
a = 3.96291 (2) ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 8.82613751 data points
Rwp = 11.40430 parameters
Rexp = 2.2130 restraints
RBragg = 10.085
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.000000.500000.554 (5)0.0101 (10)*
O_20.500000.500000.019 (7)0.0101 (10)*0.99996
Na0.000000.000000.000000.0202 (6)*0.50662
K0.000000.000000.000000.0202 (6)*0.48675
Zr0.000000.000000.000000.0202 (6)*0.00040
Nb0.500000.500000.505 (5)0.0094 (2)*0.87416
Ta0.500000.500000.505 (5)0.0094 (2)*0.09934
 
(KNN-T_643K) top
Crystal data top
Cubic, Pm3mV = 63.18 (1) Å3
Hall symbol: -P 4 2 3X-ray radiation
a = 3.982755 (19) Å
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 9.21513751 data points
Rwp = 12.11820 parameters
Rexp = 2.2050 restraints
RBragg = 11.795
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O0.500000.500000.000000.018991 (3)*
Na0.000000.000000.000000.0280 (6)*0.50683
K0.000000.000000.000000.0280 (6)*0.48633
Zr0.000000.000000.000000.0280 (6)*0.00238
Nb0.500000.500000.500000.0161 (2)*0.87397
Ta0.500000.500000.500000.0161 (2)*0.09917
 
(KNN-LT_12K) top
Crystal data top
Orthorhombic, Amm2c = 5.67188 (6) Å
Hall symbol: A 2 -2V = 125.76 (1) Å3
a = 3.93602 (3) ÅX-ray radiation
b = 5.63331 (6) Å
Data collection top
2θmin = 5.000°, 2θmax = 70.000°, 2θstep = 0.004°
Refinement top
Rp = 6.26416251 data points
Rwp = 8.05835 parameters
Rexp = 1.8140 restraints
RBragg = 6.366
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.500000.250000.287 (3)0.0002 (9)*
O20.000000.000000.550 (2)0.0002 (9)*
Na0.000000.000000.000000.0023 (5)*0.50663
K0.000000.000000.000000.0023 (5)*0.46689
Li0.000000.000000.000000.0023 (5)*0.02980
Zr0.000000.000000.000000.0023 (5)*0.00103
Nb0.500000.000000.5068 (18)0.00222 (15)*0.87418
Ta0.500000.000000.5068 (18)0.00222 (15)*0.09934
 
(KNN-LT_293K) top
Crystal data top
Orthorhombic, Amm2c = 5.66929 (11) Å
Hall symbol: A 2 -2V = 126.21 (1) Å3
a = 3.94594 (5) ÅX-ray radiation
b = 5.6418 (2) Å
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 4.49613751 data points
Rwp = 5.69946 parameters
Rexp = 1.5100 restraints
RBragg = 12.510
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.500000.250000.266 (6)0.005 (3)*
O_20.000000.000000.535 (5)0.005 (3)*
Na0.000000.000000.000000.015 (2)*0.50663
K0.000000.000000.000000.015 (2)*0.46689
Li0.000000.000000.000000.015 (2)*0.02980
Zr0.000000.000000.000000.015 (2)*0.00020
Nb0.500000.000000.489 (4)0.0040 (5)*0.87418
Ta0.500000.000000.489 (4)0.0040 (5)*0.09934
(Tetragonal) top
Crystal data top
Tetragonal, P4mmc = 4.0038 (5) Å
Hall symbol: P 4 -2V = 62.63 (1) Å3
a = 3.95505 (12) ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 4.4960 data points
Rwp = 5.69946 parameters
Rexp = 1.5100 restraints
RBragg = 16.114
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.000000.500000.57 (2)0.000 (5)*
O_20.500000.500000.04 (3)0.000 (5)*0.99996
Na0.000000.000000.000000.005 (3)*0.50662
K0.000000.000000.000000.005 (3)*0.46688
Li0.000000.000000.000000.005 (3)*0.02980
Zr0.000000.000000.000000.005 (3)*0.00040
Nb0.500000.500000.501 (16)0.0101 (14)*0.87416
Ta0.500000.500000.501 (16)0.0101 (14)*0.09934
 
(KNN-LT_383K) top
Crystal data top
Tetragonal, P4mmc = 4.02479 (3) Å
Hall symbol: P 4 -2V = 62.95 (1) Å3
a = 3.95496 (2) ÅX-ray radiation
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 6.07913751 data points
Rwp = 8.05130 parameters
Rexp = 1.2130 restraints
RBragg = 8.644
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O_10.000000.500000.570 (2)0.0075 (8)*
O_20.500000.500000.049 (4)0.0075 (8)*0.99996
Na0.000000.000000.000000.0163 (6)*0.50662
K0.000000.000000.000000.0163 (6)*0.46688
Li0.000000.000000.000000.0163 (6)*0.02980
Zr0.000000.000000.000000.0163 (6)*0.00040
Nb0.500000.500000.517 (2)0.00686 (16)*0.87416
Ta0.500000.500000.517 (2)0.00686 (16)*0.09934
 
(KNN-LT_693K) top
Crystal data top
Cubic, Pm3mV = 63.09 (1) Å3
Hall symbol: -P 4 2 3X-ray radiation
a = 3.98094 (2) Å
Data collection top
2θmin = 5.000°, 2θmax = 60.000°, 2θstep = 0.004°
Refinement top
Rp = 7.04413751 data points
Rwp = 9.05923 parameters
Rexp = 1.7400 restraints
RBragg = 9.325
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O0.500000.500000.000000.0180 (7)*
Na0.000000.000000.000000.0282 (6)*0.50683
K0.000000.000000.000000.0282 (6)*0.46678
Li0.000000.000000.000000.0282 (6)*0.03004
Nb0.500000.500000.500000.01307 (19)*0.87397
Ta0.500000.500000.500000.01307 (19)*0.09917
Zr0.000000.000000.000000.0282 (6)*0.00238
 

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