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Antimony-containing solid solutions isostructural with bismuth tungstate, Bi 2 WO 6 , have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi 2 WO 6 . The Bi 2 W 1− x Sb x O 6− y solid solutions have been shown to exist in the composition range 0 ⩽ x ⩽ 0.05. We have examined the effect of Sb 5+ doping on the polymorphism and properties of Bi 2 WO 6 . In contrast to undoped Bi 2 WO 6 , antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960 °C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb 5+ for W 6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi 2 WO 6 .

Polycrystalline samples of Bi 2 W 1− x Me x O 6− y (Me = Nb, Ta) solid solutions have been prepared by solid-state reactions, and the influence of Nb and Ta substitutions for W on the polymorphism and electrical properties of Bi 2 WO 6 has been studied. The limit of the solid solutions is at x = 0.1 for Me = Nb and at x = 0.15 for Me = Ta. The distinctive features of the polymorphism of the Nb- and Ta-doped materials have been identified. According to differential scanning calorimetry data, tantalum and niobium substitutions for tungsten increase the temperature of the high-temperature, orthorhombic-to-monoclinic reconstructive phase transition and suppress the transition starting at x = 0.05 for Me = Nb and x = 0.10 for Me = Ta. As a result, the Bi 2 W 1− x Nb x O 6− y samples have an orthorhombic Aurivillius-type structure up to their melting point. The Bi 2 W 1− x Ta x O 6− y solid solutions at high temperatures consist of a mixture of an orthorhombic and a monoclinic phase. Nb and Ta doping shifts the ferroelectric phase transition to lower temperatures by more than 200 °C, thus markedly extending the stability range of the nonpolar orthorhombic paraelectric phase, which exists in a temperature range as narrow as 930–960 °C in the case of undoped Bi 2 WO 6 . The increase in oxygen vacancy concentration due to heterovalent substitutions of Nb 5+ and Ta 5+ for W 6+ leads to an increase in conductivity by two orders of magnitude relative to the unsubstituted compound.

The crystal structures of the R 3 Ag 1− δ GeSe 7 (R = La–Nd, Sm, Gd–Dy, δ = 0.06–0.28) and R 3 Ag 1− δ SiSe 7 (R = La–Nd, Sm, Gd–Dy, δ = 0–0.30) compounds were determined by means of X-ray single crystal diffraction (space group P 6 3 ): a = 1.0806(1) nm, c = 0.6111(1) nm, R 1 = 0.0280 for La 3 Ag 0.94 GeSe 7 ; a = 1.0711(1) nm, c = 0.60719(5) nm, R 1 = 0.0126 for Ce 3 Ag 0.89 GeSe 7 ; a = 1.0619(1) nm, c = 0.6070(1) nm, R 1 = 0.0387 for Pr 3 Ag 0.89 GeSe 7 ; a = 1.0621(1) nm, c = 0.60531(6) nm, R 1 = 0.0166 for Nd 3 Ag 0.87 GeSe 7 ; a = 1.0479(1) nm, c = 0.60258(8) nm, R 1 = 0.0165 for Sm 3 Ag 0.81 GeSe 7 ; a = 1.0428(1) nm, c = 0.60321(5) nm, R 1 = 0.0187 for Gd 3 Ag 0.85 GeSe 7 ; a = 1.0364(1) nm, c = 0.60399(6) nm, R 1 = 0.0274 for Tb 3 Ag 0.82 GeSe 7 ; a = 1.0271(1) nm, c = 0.6057(1) nm, R 1 = 0.0202 for Dy 3 Ag 0.72 GeSe 7 ; a = 1.0817(1) nm, c = 0.60640(4) nm, R 1 = 0.0185 for La 3 AgSiSe 7 ; a = 1.0731(1) nm, c = 0.6031(1) nm, R 1 = 0.0200 for Ce 3 AgSiSe 7 ; a = 1.0655(1) nm, c = 0.6005(1) nm, R 1 = 0.0221 for Pr 3 AgSiSe 7 ; a = 1.0602(1) nm, c = 0.5988(1) nm, R 1 = 0.0177 for Nd 3 AgSiSe 7 ; a = 1.0497(1) nm, c = 0.59466(6) nm, R 1 = 0.0378 for Sm 3 Ag 0.85 SiSe 7 ; a = 1.0433(1) nm, c = 0.59367(7) nm, R 1 = 0.0206 for Gd 3 Ag 0.81 SiSe 7 ; a = 1.0362(1) nm, c = 0.59296(5) nm, R 1 = 0.0161 for Tb 3 Ag 0.70 SiSe 7 ; a = 1.0332(1) nm, c = 0.59494(5) nm, R 1 = 0.0115 for Dy 3 Ag 0.72 SiSe 7 . Gradual decrease of the silver amount has been observed in the series of chalcogenides. It was reported that the existence of two different positions of the silver atom implies Ag deficiency. Disordered position of the silver atom can be connected to ionic conductivity of R 3 AgTSe 7 compounds.

The crystal structure of the R 3 Ag 1− δ SiS 7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23, space group P 6 3 , Pearson symbol hP 23.80 − 23.54) compounds were determined by means of X-ray single crystal diffraction ( a = 1.04168(8) nm, c = 0.57825(4) nm, R 1 = 0.0116 for La 3 Ag 0.90 SiS 7 ; a = 1.0312(1) nm, c = 0.57395(7) nm, R 1 = 0.0152 for Ce 3 Ag 0.82 SiS 7 ; a = 1.0248(1) nm, c = 0.57223(5) nm, R 1 = 0.0105 for Pr 3 Ag 0.85 SiS 7 ; a = 1.0192(1) nm, c = 0.57020(6) nm, R 1 = 0.0292 for Nd 3 Ag 0.81 SiS 7 , a = 1.0100(1) nm, c = 0.56643(6) nm, R 1 = 0.0208 for Sm 3 Ag 0.77 SiS 7 . Gradual decrease of the silver amount in the series of chalcogenides was found.

The interactions between the components in the R2Te3–M2Te–PbTe (R = Tb, Dy; M = Cu, Ag) systems at 770 K were determined using X-ray powder diffraction. The formation of the compounds R7Cu3Te12 (Ho7Cu3Te12 structure type, space group R 3 ¯ m ), RCu5Te4 (unknown structure), RAgTe2 (ErAgTe2 structure type, space group P 4 ¯ 2 1 m ) and the solid solutions R(2+x)/3Cu2−xTe2 (0 ≤ x ≤ 1) (Er2/3Cu2S2 structure type, space group P 3 ¯ ) in the R2Te3–M2Te sections was observed. No compounds exist in the R2Te3–PbTe and M2Te–PbTe sections. The formation of quaternary compounds was not observed in the investigated systems.

The crystal structure of the R6Si4S17 compounds (R = Pr, Nd and Sm) (Ce6Si4S17 structure type, space group P 1 ¯ , Pearson symbol aP54) was determined by means of X-ray single crystal diffraction (a = 0.8902(1) nm, b = 0.9934(1) nm, c = 1.4206(2) nm, α = 82.19(1)°, β = 86.94(1)°, γ = 89.40(1)°, R1 = 0.0389 for Pr6Si4S17; a = 0.8880(1) nm, b = 0.9903(1) nm, c = 1.4168(2) nm, α = 82.11(1)°, β = 87.04(1)°, γ = 89.31(1)°, R1 = 0.0226 for Nd6Si4S17; a = 0.88300(8) nm, b = 0.9779(1) nm, c = 1.4047(1) nm, α = 82.126(8)°, β = 87.338(7)°, γ = 89.018(8)°, R1 = 0.0224 for Sm6Si4S17). The Pr atoms are surrounded by distorted trigonal prisms with two (three) additional atoms or octahedra with one additional atom. Tetrahedral surrounding exists for all Si atoms. The S atoms are surrounded by three (triangles) or four (tetrahedra) atoms.

The crystal structure of the R 2 PbS 4 (R = Yb and Lu) compounds (space group Pnma , Pearson symbol oP 28, a = 1.1899(2) nm, b = 0.39015(8) nm, c = 1.4127(2) nm, R 1 = 0.0349 for Yb 2 PbS 4 and a = 1.1919(2) nm, b = 0.38890(8) nm, c = 1.4103(3) nm, R 1 = 0.0343 for Lu 2 PbS 4 ) was investigated by means of X-ray single crystal diffraction. The R atoms are surrounded by octahedra, the Pb atoms by trigonal prisms with one additional atom.

The interactions between the components in the R 2 S 3 –Cu 2 S–PbS (R = Y, Dy, Ho and Er) systems at 870 K were determined using X-ray single crystal and powder diffraction. The existence of the compounds RCuS 2 (R = Y, Dy, Ho and Er) and the solid solutions Y (2+ x )/3 Cu 2− x S 2 (0 ≤ x ≤ 0.52), Dy (2+ x )/3 Cu 2− x S 2 (0 ≤ x ≤ 0.55), Ho (2+ x )/3 Cu 2− x S 2 (0 ≤ x ≤ 0.61), Er (2+ x )/3 Cu 2− x S 2 (0 ≤ x ≤ 0.58) was confirmed in the R 2 S 3 –Cu 2 S (R = Y, Dy, Ho and Er) sections. The existence of the compounds R 2 PbS 4 (R = Y, Ho, Dy, Er) and the solid solution Dy 2+2 x /3 Pb 1− x S 4 ( x = 0.44–0.50) was established in the R 2 S 3 –PbS (R = Y, Dy, Ho and Er) sections. The formation of the compounds Y 5+ x Cu 1− x Pb 3− x S 11 ( x = 0.28), Dy 5 CuPb 3 S 11 , Ho 5 Cu 1+ x Pb 3− x /2 S 11 ( x = 0.25), Er 5 CuPb 3 S 11 in the R 2 S 3 –Cu 2 S–PbS (R = Y, Dy, Ho and Er) systems was established at the first time, the existence of the compounds R 3.33 CuPb 1.5 S 7 (R = Y, Dy, Ho and Er) and RCuPbS 3 (R = Y, Dy, Ho and Er) was confirmed.

The crystal structures of the compounds R 3 CuSiS 7 (R = Ce, Pr, Nd, Sm, Tb, Dy and Er) and R 3 CuSiSe 7 (R = La, Ce, Pr, Nd, Sm, Gd, Tb and Dy) (La 3 CuSiS 7 structure type, space group P 6 3 , Pearson symbol hP 24) were determined by means of X-ray single crystal and powder diffraction. The R atoms are surrounded by distorted trigonal prisms. A triangular surrounding exists for the Cu atoms. A tetrahedral surrounding exists for the Si atoms. The S(Se)1 and S(Se)3 atoms are surrounded by tetrahedra also. Four cations surround every S(Se)2 atom.

The crystal structures of the R 4 In 4.72 Se 13 (R = La and Ce) compounds (space group Pbam , Pearson symbol oP 43.44) were determined by means of X-ray single crystal diffraction ( a = 1.2442(3) nm, b = 2.2146(4) nm, c = 0.41969(8) nm, R 1 = 0.0426 for La 4 In 4.72 Se 13 ) and X-ray powder diffraction ( a = 1.23725(6) nm, b = 2.2144(1) nm, c = 0.41463(2) nm, R I = 0.0984 for Ce 4 In 4.72 Se 13 ). The R atoms are surrounded by trigonal prisms with two additional atoms, the In1 atoms by tetrahedra, the In2–In5 atoms by octahedra. The R-centered trigonal prisms form columns along z -axis. The chains of the In1-centered tetrahedra and In2–In5-centered octahedra are also located along z -axis.

The crystal structure of the R2PbSe4 (R = Er and Yb) compounds (space group Pnma, Pearson symbol oP28, a = 1.2541(3) nm, b = 0.40810(8) nm, c = 1.4865(3) nm, R1 = 0.0547 for Er2PbSe4 and a = 1.2501(2) nm, b = 0.40380(8) nm, c = 1.4707(3) nm, R1 = 0.0469 for Yb2PbSe4) was determined by means of X-ray single crystal diffraction. Octahedral surrounding exists for the R atoms. The Pb atoms are surrounded by trigonal prisms with one additional atom.

The crystal structure of the Yb5.5AgSe8 compound (space group F d 3 ¯ m , Pearson symbol cF58, a = 1.1530(1) nm, R1 = 0.0388) was determined by means of X-ray single crystal diffraction. The Se atoms in the structure of the Yb5.5AgSe8 compound are stacked in a close-packed arrangement with layers in the sequence ABC. The Yb1 and Yb2 atoms are located in octahedral interstices, whereas the Ag atoms are located in tetrahedral interstices. The crystal structures of the compounds YbAgSe2 (space group P212121, Pearson symbol oP16, a = 0.68168(2) nm, b = 1.35842(5) nm, c = 0.41302(1) nm, RI = 0.0804) and YxYb1−xCuYbSe3 (x = 0.11) (space group Pnma, Pearson symbol oP24, a = 1.04114(5) nm, b = 0.39777(2) nm, c = 1.31088(6) nm, RI = 0.0884) were determined using X-ray powder diffraction. The Se atoms in the structure of the YbAgSe2 compound are stacked in a close-packed arrangement with layers in the sequence AB. Half of the octahedral interstices are occupied by Yb atoms. Remaining octahedral interstices are occupied by Ag atoms. Octahedral surrounding of the atoms of the statistical mixture M (Y + Yb), trigonal prismatic of the Yb atoms and tetrahedral of the Cu atoms exist in the crystal structure of the YxYb1−xCuYbSe3 (x = 0.11) compound.

The crystal structures of the R 2 CuInS 5 (R = La, Ce, Pr, Nd, Sm) compounds (space group Pnma , Pearson symbol oP 36) were determined by means of X-ray single crystal diffraction ( a = 1.1487(2) nm, b = 0.39760(8) nm, c = 1.6911(3) nm, R 1 = 0.0250 for La 2 CuInS 5 ) and X-ray powder diffraction ( a = 1.14396(7) nm, b = 0.39361(2) nm, c = 1.6804(1) nm, R Bragg = 0.0937 for Ce 2 CuInS 5 ; a = 1.14123(6) nm, b = 0.39119(2) nm, c = 1.6737(1) nm, R Bragg = 0.0974 for Pr 2 CuInS 5 ; a = 1.13948(6) nm, b = 0.38933(2) nm, c = 1.66886(9) nm, R Bragg = 0.0853 for Nd 2 CuInS 5 ; a = 1.13671(7) nm, b = 0.38594(2) nm, c = 1.6603(1) nm, R Bragg = 0.0887 for Sm 2 CuInS 5 ). The R-centered trigonal prisms, Cu-centered tetrahedra and In-centered octahedra can be selected in the crystal structures of the R 2 CuInS 5 compounds.

The crystal structures of the RAgTe2 (R = Y, Tb, Dy, Ho and Er) compounds (space group P 4 ¯ 2 1 m , Pearson symbol tP8) were determined by means of X-ray powder diffraction: a = 0.71398(2) nm, c = 0.45947(2) nm, RI = 0.0701 (YAgTe2), a = 0.71466(3) nm, c = 0.46108(3) nm, RI = 0.0761 (TbAgTe2), a = 0.71287(3) nm, c = 0.45955(3) nm, RI = 0.0637 (DyAgTe2), a = 0.71033(3) nm, c = 0.45713(3) nm, RI = 0.0755 (HoAgTe2) and X-ray single crystal diffraction: a = 0.7091(1) nm, c =0.45650(9) nm, R1 = 0.0366 (ErAgTe2). The Te atoms in the structure of the RAgTe2 compounds are stacked in a close-packed arrangement with layers in the sequence AB. Half of the octahedral interstices are occupied by the R atoms. The Ag atoms are located in remaining octahedral interstices, but they are shifted from the centers of the respective octahedra and tetrahedral surrounding really exists for Ag.

Crystal structures of R 3 CuGeS 7 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy and Er) (La 3 CuSiS 7 structure type, space group P 6 3 , Pearson symbol hP24 ) were determined by means of X-ray single crystal diffraction ( a = 1.0225(1) nm, c = 0.58350(7) nm, R 1 = 0.0213 for Ce 3 CuGeS 7 ; a = 1.0168(1) nm, c = 0.58223(7) nm, R 1 = 0.0284 for Pr 3 CuGeS 7 ; a = 1.0123(1) nm, c = 0.57942(7) nm, R 1 = 0.0240 for Nd 3 CuGeS 7 ) and X-ray powder diffraction ( a = 1.00144(1) nm, c = 0.57714(1) nm, R Bragg = 0.0968 for Sm 3 CuGeS 7 ; a = 0.99428(1) nm, c = 0.57592(1) nm, R Bragg = 0.0863 for Gd 3 CuGeS 7 ; a = 0.98863(1) nm, c = 0.57535(1) nm, R Bragg = 0.0838 for Tb 3 CuGeS 7 ; a = 0.98371(3) nm, c = 0.57552(3) nm, R Bragg = 0.0802 for Dy 3 CuGeS 7 ; a = 0.97415(1) nm, c = 0.57835(1) nm, R Bragg = 0.0709 for Er 3 CuGeS 7 ). The structures are built up from three-dimensional network of RS 8 distorted square antiprisms sharing edges, consolidated by GeS 4 tetrahedra and CuS 3 triangles sharing edges with the antiprisms.

The crystal structures of the R3CuGeSe7 compounds (R = Ce, Pr, Nd, Sm, Gd, Tb and Ho) (La3CuSiS7 structure type, space group P63, Pearson symbol hP24) were determined by means of X-ray single crystal diffraction (a = 1.0643(1) nm, c = 0.60973(7) nm, R1 = 0.0269 for Ce3CuGeSe7; a = 1.0559(1) nm, c = 0.6084(1) nm, R1 = 0.0301 for Pr3CuGeSe7; a = 1.0519(1) nm, c = 0.60707(9) nm, R1 = 0.0305 for Nd3CuGeSe7) and X-ray powder diffraction (a = 1.04216(3) nm, c = 0.60447(3) nm, RBragg = 0.0862 for Sm3CuGeSe7; a = 1.03491(8) nm, c = 0.60395(7) nm, RBragg = 0.0932 for Gd3CuGeSe7; a = 1.02940(5) nm, c = 0.60387(4) nm, RBragg = 0.0734 for Tb3CuGeSe7; a = 1.01978(7) nm, c = 0.60612(6) nm for Ho3CuGeSe7). The R atoms are surrounded by distorted trigonal prisms. A triangular surrounding exists for the Cu atoms. A tetrahedral surrounding exists for the Ge atoms.

Single phase samples of the R 6 Pb 2 Se 11 (R = Y, Dy and Ho) compounds were obtained using high temperature synthesis. Crystal structure of Ho 6 Pb 2 Se 11 (Y 6 Pb 2 Se 11 type, space group Cmcm , Pearson symbol oC76 , lattice parameters: a = 0.40603(7) nm, b = 1.3397(3) nm, c = 3.7542(5) nm) was reinvestigated by means of X-ray single crystal diffraction and refined down to R1 = 0.0572. Magnetic properties of the R 6 Pb 2 Se 11 compounds were studied in wide ranges of temperature and magnetic field. Dy 6 Pb 2 Se 11 and Ho 6 Pb 2 Se 11 were found to order antiferromagnetically at T N = 2.2 and 2.4 K, respectively, whereas weak diamagnetism was established for Y 6 Pb 2 Se 11 .

The phase equilibria in the Y2Te3–Cu2Te–PbTe system at 870 K were determined. The formation of the YCuTe2–Y2/3Cu2Te2 compound (Er2/3Cu2S2 structure type, space group P 3 ¯ , a = 0.42970(2) nm, c = 0.69087(5) nm, RI = 0.0582 for YCuTe2) was observed. The crystal structures of new compounds Y7Cu3Te12 (Ho7Cu3Te12 structure type, space group R 3 ¯ m , Pearson symbol hR27-5, a = 0.43150(6) nm, c = 4.1790(8) nm, R1 = 0.0387) and YCu0.264Te2 (LaCu0.28Te2, space group Pbcm, Pearson symbol oP13.056, a = 0.7572(1) nm, b = 0.8164(1) nm, c = 0.6085(1) nm, R1 = 0.0597) were determined by means of X-ray single crystal diffraction. No quaternary compounds exist in the Y2Te3–Cu2Te–PbTe system at 870 K.

The interactions between the components in the Ho2Se3–Cu2Se–PbSe and Er2Se3–Cu2Se–PbSe systems at 870 K were determined using X-ray single crystal and powder diffraction. The existence of the compounds with compositions RCuSe2–R2/3Cu2Se2 (Er2/3Cu2S2 structure type, space group P 3 ¯ , a = 0.40563(1) nm, c = 0.64542(3) nm, RI = 0.0737 for HoCuSe2 and a=0.40407(1) nm, c = 0.64420(3) nm, RI = 0.0660 for ErCuSe2) and RCu5Se4 (unknown structure) was confirmed in the R2Se3–Cu2Se (R = Ho, Er) sections. The existence of the compounds Ho6Pb2Se11 (Y6Pb2Se11 structure type, space group Cmcm, a = 0.40561(2) nm, b = 1.34018(6) nm, c = 3.7525(1) nm) and Er2PbSe4 (CaFe2O4 structure type, space group Pnma, a = 1.2554(2) nm, b = 0.40778(5) nm, c = 1.4885(2) nm, RI = 0.0914) was confirmed in the R2Se3–PbSe (R = Ho, Er) sections. The existence of the compounds Ho3.33CuPb1.5Se7 (Lu3.33CuPb1.5Se7 structure type, space group Cm, a = 1.35314(8) nm, b = 0.40819(2) nm, c = 1.25609(7) nm, β = 104.577(3)°) and HoCuPbSe3 (β-BaLaCuSe3 structure type, space group Pnma, a = 1.0516(2) nm, b = 0.40470(8) nm, c = 1.3410(3) nm, R1 = 0.0541) in the Ho2Se3–Cu2Se–PbSe system was confirmed. The formation of the compounds Er5CuPb3Se11 (Er5CuPb3Se11 structure type, space group Cmcm, a = 0.40688(2) nm, b = 1.34607(7) nm, c = 3.8040(2) nm), Er3.33CuPb1.5Se7 (Lu3.33CuPb1.5Se7 structure type, space group Cm, a = 1.35018(7) nm, b = 0.40693(2) nm, c = 1.25433(6) nm, β = 104.492(2)°) and ErCuPbSe3 (β-BaLaCuSe3 structure type, space group Pnma, a = 1.04846(8) nm, b = 0.40424(3) nm, c = 1.34143(7) nm) in the Er2Se3–Cu2Se–PbSe system was confirmed.