Langbeinites

Langbeinites are a family of crystalline substances based on the structure of langbeinite with general formula M₂M^'₂(SO₄)₃, where M is a large univalent cation such as potassium, rubidium, caesium, or ammonium), and M^' is a small divalent cation for example (magnesium, calcium, manganese, iron, cobalt, nickel, copper, zinc or cadmium). The sulfate group, SO₄²⁻, can be substituted by other tetrahedral anions with a double negative charge such as tetrafluoroberyllate BeF₄²⁻, selenate (SeO₄²⁻), chromate (CrO₄²⁻), molybdate (MO₄²⁻), or tungstates. Although monofluorophosphates are predicted, they have not been described. By redistributing charges other anions with the same shape such as phosphate also form langbeinite structures. In these the M^' atom must have a greater charge to balance the extra three negative charges.

At higher temperatures the crystal structure is cubic P2₁3.[1] However, the crystal structure may change to lower symmetries at lower temperatures, for example, P2₁, P1, or P2₁2₁2₁.[1] Usually this temperature is well below room temperature, but in a few cases the substance must be heated to acquire the cubic structure.

Crystal structure

The crystal structures of langbeinites consist of a network of oxygen vertex-connected tetrahedral polyanions (such as sulfate) and distorted metal ion-oxygen octahedra.[2] The unit cell contains four formula units. In the cubic form the tetrahedral anions are slightly rotated from the main crystal axes. When cooled, this rotation disappears and the tetrahedra align, resulting in lower energy as well as lower crystal symmetry.

Examples

Sulfates include dithallium dicadmium sulfate,[3] Dirubidium dicadmium sulfate[4] dipotassium dicadmium sulfate,[5] dithallium manganese sulfate.[6] dirubidium dicalcium trisulfate.[7]

Selenates include diammonium dimanganese selenate.[1] A diammonium dicadmium selenate langbeinite could not be crystallised from water, but a trihydrate exists.[8]

Chromate based langbeinites include dicaesium dimanganese chromate.[1]

Molybdates include Rb₂Co₂(MoO₄)₃.[1] Potassium members are absent, as are zinc and copper containing solids, which all crystallize in different forms. Manganese, magenesium, cadmium and some nickel double molydates exist as langbeinites.[9]

Double tungstates of the form A₂B₂(WO₄)₃ are predicted to exist in the langbeinite form.[10]

Examples with tetrafluroberyllate include dipotassium dimanganese tetrafluoroberyllate K₂Mn₂(BeF₄)₃,[11]

Other tetrafluoroberyllates may include Rb₂Mg₂(BeF₄)₃ Tl₂Mg₂(BeF₄)₃ Tl₂Mn₂(BeF₄)₃ Rb₂Ni₂(BeF₄)₃ Tl₂Ni₂(BeF₄)₃ Rb₂Zn₂(BeF₄)₃ Tl₂Zn₂(BeF₄)₃ Cs₂Ca₂(BeF₄)₃ Rb₂Ca₂(BeF₄)₃ RbCsMnCd(BeF₄)₃ Cs₂MnCd(BeF₄)₃ RbCsCd₂(BeF₄)₃ Cs₂Cd₂(BeF₄)₃. Tl₂Cd₂(BeF₄)₃ (NH₄)₂Cd₂(BeF₄)₃ KRbMnCd(BeF₄)₃ K₂MnCd(BeF₄)₃ Rb₂MnCd(BeF₄)₃ Rb₂Cd₂(BeF₄)₃ RbCsCo₂(BeF₄)₃ (NH₄)₂Co₂(BeF₄)₃ K₂Co₂(BeF₄)₃ Rb₂Co₂(BeF₄)₃ Tl₂Co₂(BeF₄)₃ RbCsMn₂(BeF₄)₃ Cs₂Mn₂(BeF₄)₃ RbCsZn₂(BeF₄)₃ (NH₄)₂Mg₂(BeF₄)₃ (NH₄)₂Mn₂(BeF₄)₃ (NH₄)₂Ni₂(BeF₄)₃ (NH₄)₂Zn₂(BeF₄)₃ KRbMg₂(BeF₄)₃ K₂Mg₂(BeF₄)₃. KRbMn₂(BeF₄)₃ K₂Mn₂(BeF₄)₃ K₂Ni₂(BeF₄)₃ K₂Zn₂(BeF₄)₃[12]

The phosphate containing langbeinites were found in 1972 with the discovery of KTi₂(PO₄)₃, and since then a few more phosphates that also contain titanium have been found such as Na₂FeTi(PO₄), Na₂CrTi(PO₄)₃. By substituting metals in A₂MTi(PO₄)₃, A from K, Rb, Cs, and M from Cr, Fe or V other langbeinites are made. The NASICON-type structure competes for these kinds of phosphates, so not all possibilities are langbeinites.[1] Other phosphate based substances include K₂YTi(PO₄)₃ K₂ErTi(PO₄)₃ K₂YbTi(PO₄)₃, K₂CrTi(PO₄)₃[1] K₂AlSn(PO₄)₃[13] Rb₂YbTi(PO₄)₃.[14] Sodium barium diiron tris-(phosphate) NaBaFe₂(PO₄)₃ is yet another variation with the same structure but differently charged ions.[15] Most phosphates of this kind of formula do not form langbeinites, instead crystallise in the NASICON structure with archetype Na₃Zr₂(PO₄)(SiO₄)₂.[1]

A langbeinite with arsenate is known to exist by way of K₂ScSn(AsO₄)₃.[16]

Properties

Physical properties

Lanbeinite crystals can show ferroelectric or ferroelastic properties.[1] Diammonium dicadmium sulfate identified by Jona and Pepinsky[17] with a unit cell size of 10.35 Å becomes ferroelectric when the temperature drops below 95K.[18] The phase transition temperature is not fixed, and can vary depending on the crystal or history of temperature change. So for example the phase transition in diammonium dicadmium sulfate can occur between 89 and 95 K.[19] Under pressure the highest phase transition temperature increases. ∂T/∂P = 0.0035 degrees/bar. At 824 bars there is a triple point with yet another transition diverging at a slope of ∂T/∂P = 0.103 degrees/bar.[20] For dipotassium dimanganese sulfate pressure causes the transition to rise at the rate of 6.86 °C/kbar. The latent heat of the transition is 456 cal/mol.[21]

Dithallium dicadmium sulfate was shown to be ferroelectric in 1972.[22]

Dipotassium dicadmium sulfate is thermoluminescent with stronger outputs of light at 350 and 475 K. This light output can be boosted forty times with a trace amount of samarium.[23] Dipotassium dimagnesium sulfate doped with dysprosium develops thermoluminescence and mechanoluminescence after being irradiated with gamma rays.[24] Since gamma rays occur naturally, this radiation induced thermoluminescence can be used to date evaporites in which langbeinite can be a constituent.[25]

At higher temperatures the crystals take on cubic form, whereas at the lowest temperatures they can transform to an orthorhombic crystal group. For some types there are two more phases, and as the crystal is cooled it goes from cubic, to monoclinic, to triclinic to orthorhombic. This change to higher symmetry on cooling is very unusual in solids.[26] For some langbeinites only the cubic form is known, but that may be because it has not been studied at low enough temperatures yet. Those that have three phase transitions go through these crystallographic point groups: P2₁3 – P2₁ – P1 – P2₁2₁2₁, whereas the single phase change crystals only have P2₁3 – P2₁2₁2₁.

K₂Cd₂(SO₄)₃ has a transition temperature above room temperature, so that it is ferroelectric in standard conditions. The orthorhombic cell size is a=10.2082 Å, b=10.2837 Å, c=10.1661 Å.[27]

Where the crystals change phase there is a discontinuity in the heat capacity. The transitions may show thermal hysteresis.[28]

Different cations can be substituted so that for example K₂Cd₂(SO₄)₃ and Tl₂Cd₂(SO₄)₃ can form solid solutions for all ratios of thallium and potassium. Properties such as the phase transition temperature and unit cell sizes vary smoothly with the composition.[29]

Langbeinites containing transition metals can be coloured. For example, cobalt langbeinite shows a broad absorption around 555 nm due to the cobalt ⁴T_1g(F)→⁴T_1g(P) electronic transition.[30]

The enthalpy of formation (ΔfHm) for solid (NH₄)₂Cd₂(SO₄)₃ at 298.2K is −3031.74±0.08 kJ/mol, and for K₂Cd₂(SO₄)₃ it is －3305.52±0.17 kJ/mol.[31]

Sulfates

		formula weight	comment	transition temperature K			density	cell size	refractive
elements	formula	g/mol	symmetries	1	2	3[32]		Å	index
NaMg	Na2Mg2(SO4)3	382.78	3 phases, 1-2,>3	250	350	575[33]
KMg	K2Mg2(SO4)3	414.99	4 phases Langbeinite	51	54.9	63.8	2.832[34]	9.9211[35]	1.536[36]
RbMg	Rb2Mg2(SO4)3	507.73	made				3.367[37]	10.0051[37]	1.556[37]
CsMg	Cs2Mg2(SO4)3	602.61	no compound[10]
(NH4)Mg	(NH4)2Mg2(SO4)3	372.87	Efremovite[38]	241[39]	220[39]		2.49[40]	9.979[40]
TlMg	Tl2Mg2(SO4)3	745.56	≥3 phase		227.8[39]	330.8[39]
KCaMg	K2CaMg(SO4)3	430.77	made				2.723[41]	10.1662[41]	1.525[41]
KCa	K2Ca2(SO4)3	446.54	4 phases calciolangbeinite[42][43]	457			2.69 2.683[44]	10.429Å a=10.334 b=10.501 c=10.186	Nα=1.522 Nβ=1.526 Nγ=1.527
RbCa	Rb2Ca2(SO4)3	539.28	2 phases	183			3.034[45]	10.5687[45]	1.520[45]
CsCa	Cs2Ca2(SO4)3	634.15					3.417[46][47]	10.7213	1.549
TlCa			no compound[10]
(NH4)Ca	(NH4)2Ca2(SO4)3	404.42	made	158			2.297[48]	10.5360[48]	1.532[48]
NH4V	(NH4)2V2(SO4)3	colour clear green[49]					2.76[50]	10.089[49]
KMn manganolangbeinite[51]	K2Mn2(SO4)3	476.26	2 phases pale pink[52]	191			3.02[35]	10.014[35] (orthorhombic) a=10.081, b=10.108, c=10.048 Å[53]	1.576[52]
RbMn[54]	Rb2Mn2(SO4)3	569	made				3.546[55]	10.2147[55]	1.590[55]
CsMn	Cs2Mn2(SO4)3	663.87	predicted[10]
(NH4)Mn	(NH4)2Mn2(SO4)3	434.14	made				2.72[40]	10.1908[56]
TlMn	Tl2Mn2(SO4)3	806.83	made				5.015[57]	10.2236[57]	1.722[57]
KFe	K2Fe2(SO4)3	478.07	made	?130
RbFe			predicted[10]
TlFe		808.64	exists[10]
NH4Fe	(NH4)2Fe2(SO4)3[49]	435.95	mineralFerroefremovite				2.84[40]	10.068[40]	1.574[58]
KCo	K2Co2(SO4)3	484.25	2 phases deep purple	126			3.280[34]	9.9313[35]	1.608[59]
RbCo	Rb2Co2(SO4)3	576.99	made				3.807[60]	10.0204[60]	1.602[60]
CsCo		671.87
(NH4)Co	(NH4)2Co2(SO4)3	442.13	made				2.94[40]	9.997[40]
TlCo	Tl2Co2(SO4)3	813.82	made				5.361[61]	10.0312	1.775
KNi	K2Ni2(SO4)3	483.77	made[62] light greenish yellow[63]				3.369[34]	9.8436[63]	1.620[63]
RbNi	Rb2Ni2(SO4)3	576.51	made				3.921[64]	9.9217[64]	1.636[64]
CsNi		671.39	predicted[10]
(NH4)Ni	(NH4)2Ni2(SO4)3	441.65	made[62]	160			3.02[40]	9.904[40]
TlNi	Tl2Ni2(SO4)3	814.34	predicted[10]
RbCu			predicted[10]
CsCu			predict not[10]
TlCu			predicted[10]
KZn	K2Zn2(SO4)3	497.1	4 phases	75	138		3.376[34]	9.9247[65]	1.592[65]
RbZn			predicted[10]
CsZn			predict not[10]
TlZn			predicted[10]
KCd	K2Cd2(SO4)3	591.21	2 phases	432			2.615 3.677[66]	a=10.212 b=10.280 c=10.171	Nα=1.588 Nγ=1.592
RbCd	Rb2Cd2(SO4)3	683.95	4 phases	66	103	129	4.060[35][67]	10.3810[35][67]	1.590[67]
(NH4)Cd	(NH4)2Cd2(SO4)3	549.09	4 phases			95	3.288[35]	10.3511[35]
TlCd	Tl2Cd2(SO4)3	921.78	4 phases	92	120	132	5.467[35]	10.3841[35]	1.730[68]

Fluoroberyllates

elements	formula	formula weight	cell Å	volume	density	comment
KMnBe	K2Mn2(BeF4)3[11]					4 phases transition at 213
KMg[69]	K2Mg2(BeF4)3		9.875	962.8	1.59
(NH4)Mg	(NH4)2Mg2(BeF4)3[69]		9.968		1.37
KRbMg	KRbMg2(BeF4)3[69]		9.933		1.72
RbMg	Rb2Mg2(BeF4)3[69]		9.971		1.91
TlMg	Tl2Mg2(BeF4)3[69]		9.997		2.85	(CsMg does not exist)[69]
KNi	K2Ni2(BeF4)3[69]		9.888		1.86
RbNi	Rb2Ni2(BeF4)3[69]		9.974		2.19
TlNi	Tl2Ni2(BeF4)3[69]		9.993		3.13
KCo	K2Co2(BeF4)3[69]		9.963	988	1.82
(NH4)Co	(NH4)2Co2(BeF4)3[69]		10.052		1.61
RbCo	Rb2Co2(BeF4)3[69]		10.061		2.14
TlCo	Tl2Co2(BeF4)3[69]		10.078		3.05
RbCsCo	RbCsCo2(BeF4)3[69]		10.115		2.28
KZn	K2Zn2(BeF4)3[69]		9.932		1.89
(NH4)Zn	(NH4)Zn2(BeF4)3[69]		10.036		1.67
RbZn	Rb2Zn2(BeF4)3[69]		10.035		2.20
TlZn	Tl2Zn2(BeF4)3[69]		10.060		3.14
RbCsZn	RbCsZn2(BeF4)3[69]		10.102		2.36
KMn	K2Mn2(BeF4)3[69]		10.102		1.72
KRbMn	KRbMn2(BeF4)3[69]		10.187		1.82
(NH4)Mn	(NH4)2Mn2(BeF4)3[69]		10.217		1.50
RbMn	Rb2Mn2(BeF4)3[69]		10.243		2.00
TlMn	Tl2Mn2(BeF4)3[69]		10.255		2.87
RbCsMn	RbCs2Mn2(BeF4)3[69]		10.327		2.12
CsMn	Cs2Mn2(BeF4)3[69]		10.376		2.26
KMnCd	K2MnCd(BeF4)3[69]		10.133		1.92
KRbMnCd	KRbMnCd(BeF4)3[69]		10.220		2.04
RbMnCd	Rb2MnCd(BeF4)3[69]		10.133		1.92
RbCsMnCd	RbCsMnCd(BeF4)3[69]		10.380		2.28
CsMnCd	Cs2MnCd(BeF4)3[69]		10.451		2.41
(NH4)Cd	(NH4)2Cd2(BeF4)3[69]		10.342		1.87
RbCd	Rb2Cd2(BeF4)3[69]		10.385		2.32
TlCd	Tl2Cd2(BeF4)3[69]		10.402		3.16
RbCsCd	RbCs2Cd2(BeF4)3[69]		10.474		2.43
CsCd	Cs2Cd2(BeF4)3[69]		10.558		2.53
RbCsCdCa	RbCs2CdCa(BeF4)3[69]		10.501		2.15
RbCa	Rb2Ca2(BeF4)3[69]		10.480		1.74
RbCsCa	RbCsCa2(BeF4)3[69]		10.583		1.86
CsCa	Cs2Ca2(BeF4)3[69]		10.672		1.98

Phosphates

substance	formula weight	unit cell edge Å	density	comment
LiCs2Y2(PO4)3[70]	735.48	10.5945	4.108
LiRb2Y2(PO4)3[71]				non-linear optical
K2YTi(PO4)3[1]	578.25	10.1053	3.192
K2ErTi(PO4)3[1]	584.03	10.094	3.722
K2YbTi(PO4)3[1]	499.89	10.1318	3.772
K2CrTi(PO4)3[1]	462.98	9.8001	3.267
(NH4)(H3O)Ti^IIITi^IV(PO4)3[72]	417.71	9.9384
K2Ti2(PO4)3[73]	458.84	9.8688		Also K2−x; dark blue
Rb2Ti2(PO4)3[73]	551.58	9.9115
Tl2Ti2(PO4)3[73]	789.41	9.9386
Na2FeTi(PO4)3[74]		9.837
Na2CrTi(PO4)3[74]		9.775
K2Mn0.5Ti1.5(PO4)3[75]		9.903	3.162	dark brown
K2Co0.5Ti1.5(PO4)3[75]		9.844	3.233	dark brown
Rb4NiTi3(PO4)6[76]	1113.99÷2	9.9386
K2AlTi(PO4)3[77]	437.96	9.7641	3.125	colourless
Li2Zr2(PO4)3[78]	481.24
K2(Ce,...,Lu)Zr(PO4)3[79]	594.45...629.3	10.29668
Rb2FeZr(PO4)3[80]	602.92	10.1199
K2FeZr(PO4)3[81]	510.18	10.0554		dark grey Note Na2FeZr(PO4)3 is not a langbeinite.[82]
K2YZr(PO4)3[83]	543.24	10.3346		random Y and Zr
K2GdZr(PO4)3[83]	611.58	10.3457		random Gd and Zr
K2YHf(PO4)3[84]	630.51	10.3075	3.824
Li(H2O)2Hf2(PO4)3[85]	684.87	10.1993
K2BiHf(PO4)3[86]	750.58
Li(H2O)2Zr2(PO4)3[78]	510.33	10.2417
K2AlSn(PO4)3	508.78	9.798[13]
K2CrSn(PO4)3		9.8741
K2InSn(PO4)3		10.0460
K2FeSn(PO4)3		9.921
K2YbSn(PO4)3		10.150
K4Al3Ta(PO4)6[87]	988.11	9.7262
K4Cr3Ta(PO4)6[87]	1063.16	9.8315
K4Fe3Ta(PO4)6[87]	1074.70	9.9092
K4Tb3Ta(PO4)6		10.3262[88]
K4Fe3Nb(PO4)6[87]	986.66	9.9092
KBaEr2(PO4)3[89]	795.857
RbBaEr2(PO4)3[89]	842.227
CsBaEr2(PO4)3[89]	889.665
(Rb,Cs)2(Pr,Er)Zr(PO4)3[89]
KCsFeZrP3O12	603.99	10.103[90]
CaFe3O(PO4)3[91]	508.53
SrFe3O(PO4)3[91]	556.1
PbFe3O(PO4)3[91]	675.6
KSrFe2(PO4)3[92]	523.32	9.809	3.68	yellowish
Pb1.5V^IV2(PO4)3	697.6	9.7818	4.912[93]
K2TiV(PO4)[94]		9.855		green
BaTiV(PO4)[94]		9.922	3.54	at high temperature >950 °C dark grey
KBaV2(PO4)[94]		9.873		greenish yellow
Ba1.5V2(PO4)[94]		9.884		grey
Ba1.5Fe^3+2(PO4)3[95][96]	602.59
KSrSc2(PO4)3[97]	501.54
Rb0.743K0.845Co0.293Ti1.707(PO4)3[98]		9.8527
K2BiZr(PO4)6[99]	663.32	10.3036
KBaSc2(PO4)3[100]	503.25
KBaRZrP2SiO12 R=La, Nd, Sm, Eu, Gd, Dy, Y[2]
KBaYSnP2SiO12[2]	666.07
KBaFe2(PO4)3[101]	525.03	9.8732 (at 4K)
KBaCr2(PO4)3[102]	517.33	9.7890
Rb2FeTi(PO4)3[103]	511.56	9.8892		Na2FeTi(PO4)3 has NZP structure[82]
KBaMgTi(PO4)3[104]	485.51	9.914		KSrMgTi crystallises in kosnarite form
KPbMgTi(PO4)3[104]	555.39	9.8540		KSrMgTi in kosnarite form
RbBaMgTi(PO4)3[104]		9.954	531.88	CsBa does not form
RbPbMgTi(PO4)3[104]	601.76	9.9090		CsPb does not form
KSrMgZr(PO4)3[104]	479.16	10.165
KPbMgZr(PO4)3[104]	598.74	10.111
KBaMgZr(PO4)3[104]	528.87	10.106
RbSrMgZr(PO4)3[104]	525.53	10.218
RbPbMgZr(PO4)3[104]	645.11	10.178
RbBaMgZr(PO4)3[104]	575.24	10.178
CsSrMgZr(PO4)3[104]	572.97	10.561		over 1250 °C forms kosnarite phase
Ba3In4(PO4)6[105]		10.1129
Ba3V4(PO4)6[106]	1185.58	9.8825	4.08	yellow-green
KPbCr2(PO4)3[107]		9.7332
KPbFe2(PO4)3[107]		9.8325		beige
K4NiHf3(PO4)6[108]	660.192 (half)	10.12201	4.228	yellow

Phosphate silicates

substance	formula weight	unit cell edge Å	density	comment
K2Sn2(PO4)2SiO4[109]				Stable to 650°C
K2Zr2(PO4)2SiO4[109]				Stable to 1000°C

Vanadates

The orthovanadates have four formula per cell, with a slightly distorted cell that has orthorhombic symmetry.

	formula weight	comment	Cell dimensions Å			Volume	density	refractive
Formula	g/mol	symmetries	a	b	c			index
LiBaCr2(VO4)3[110]	593.08	Orthorhombic	9.98	10.52	9.51	998	4.02
NaBaCr2(VO4)3[110]	609.13	Orthorhombic	9.99	10.52	9.53	1002	4.09
AgBaCr2(VO4)3[110]	694.00	Orthorhombic	10.02	10.53	9.53	1005	4.62

Arsenates

substance	formula weight	unit cell edge Å	density
K2ScSn(AsO4)3[111]	658.62	10.3927
Zr2NH4(AsO4)3.H2O[112]	632.558	10.532	3.379

Selenates

Langbeinite structured double selenates are difficult to make, perhaps because selenate ions arranged around the dication leave space for water, so hydrates crystallise from double selenate solutions. For example, when ammonia selenate and cadmium selenate solution is crystallized it forms diammonium dicadmium selenate trihydrate: (NH₄)₂Cd₂(SeO₄)₃•3H₂O and when heated it loses both water and ammonia to form a pyroselenate rather than a langbeinite.[113]

substance	formula weight	unit cell edge Å	density	note
(NH4)2Mn2(SeO4)3[114]	574.83	10.53	3.26	forms continuous series with SO4 too

Molybdates

-

substance	formula weight	unit cell edge Å	density
Cs2Cd2(MoO4)3[115]	970.5	11.239
Rb2Co2(MoO4)3	768.7
Cs2Co2(MoO4)3[116]
Cs2Ni2(MoO4)3[117]	863.01	10.7538
(H3O)2Mn2(MoO4)3[118]	627.75	10.8713
K2Mn2(MoO4)3[119]

Tungstates

substance	formula weight	unit cell edge Å	density
Rb2Mg2(WO4)3[120]	963.06	10.766
Cs2Mg2(WO4)3[120]	1057.93	10.878

Preparation

Diammonium dicadmium sulfate can be made by evaporating a solution of ammonium sulfate and cadmium sulfate.[19] Dithallium dicadmium sulfate can be made by evaporating a water solution at 85 °C.[22] Other substances may be formed during crystallisation from water such as Tutton's salts or competing compounds like Rb₂Cd₃(SO₄)₄·5H₂O.[121]

Potassium and ammonium nickel langbeinite can be made from nickel sulfate and the other sulfates by evaporating a water solution at 85 °C.[62]

Dipotassium dizinc sulfate can be formed into large crystals by melting zinc sulfate and potassium sulfate together at 753K. A crystal can be slowly drawn out of the melt from a rotating crucible at about 1.2 mm every hour.[122]

Li(H₂O)₂Hf₂(PO₄)₃ can be made by heating HfCl₄, Li₂B₄O₇, H₃PO₄, water and hydrochloric acid to 180 °C for eight days under pressure.[85] Li(H₂O)₂Hf₂(PO₄)₃ converts to Li₂Hf₂(PO₄)₃ on heating to 200 °C.[78]

The sol-gel method produces a gel from a solution mixture, which is then heated. Rb₂FeZr(PO₄)₃ can be made by mixing solutions of FeCl₃, RbCl, ZrOCl₂, and dripping in H₃PO₄. The gel produced was dried out at 95 °C and then baked at various temperatures from 400 to 1100 °C.[80]

Langbeinites crystals can be made by the Bridgman technique, Czochralski process or flux technique.

A Tutton's salt may be heat treated and dehydrate, e.g. (NH₄)₂Mn₂(SeO₄)₃ can be made from (NH₄)₂Mn(SeO₄)₃·6(H₂O) heated to 100 °C, forming (NH₄)₂(SeO₄) as a side product.[123] Similarly the ammonium vandadium Tutton's salt, (NH₄)₂V(SO₄)₂, heated to 160 °C in a closed tube produces (NH₄)₂V₂(SO₄)₃. At lower temperatures a hydroxy compound is formed.[49]

Use

Few uses have been made of these substances. Lanbeinite itself can be used as an "organic" fertiliser with potassium, magnesium and sulfur, all needed for plant growth. Electrooptic devices could be made from some of these crystals, particularly those that have cubic transition temperatures as temperatures above room temperature. Research continues into this. Ferroelectric crystals could store information in the location of domain walls.

The phosphate langbeinites are insoluble, stable against heat, and can accommodate a large number of different ions, and have been considered for immobilizing unwanted radioactive waste.[124]

Rare earth containing zirconium phosphate langbeinites have been investigated for use in white LEDs and plasma displays.[99] Langbeinites that contain bismuth are photoluminescent.[99] In case of iron-containing ones complex magnetic behavior may be found.[125]

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