ライフサイエンスコーパス: clathrate

1 ngular polyhedra as in cage compounds (e.g., clathrates).

2 rphous clathrate transforms into crystalline clathrate.

3 cient, hydrogen-encapsulated, type I silicon clathrate.

4 al to the expected composition of the type-I clathrate.

5 ations confirm the stability of 2D amorphous clathrate.

6 and sI crystalline nuclei yield crystalline clathrates.

7 s that affect the crystallization pathway of clathrates.

8 as an intermediate in the crystallization of clathrates.

9 f low (13)C is rapidly released from methane clathrates.

10 tres of the surface, or the decomposition of clathrates.

11 te and the proposed speciation in the liquid clathrates.

12 e nucleation and growth of confined hydrogen clathrates.

13 ucture dictate the formation of 2D amorphous clathrates.

14 iconducting materials based on tunable III-V clathrates.

15 drophobic solutes, matching those in ice and clathrates.

16 nsive structural ordering resembling that in clathrates.

17 n addition, 6-fold (C6) benzene rotations in clathrate 1A were found to be directly correlated to the

18 Pseudopolymorphic crystals of a benzene clathrate (1A) and a desolvated form (1B) were analyzed

19 h phases were determined: 9 +/- 1 GPa for Xe clathrate A with structure I (cubic, a = 11.595 +/- 0.00

20 tudied the formation of methane and hydrogen clathrates, a group of inclusion compounds consisting of

21 osed of the pentagonal dodecahedra common to clathrates along with a unique 22-vertex polyhedron with

22 14.6 kcal/mol were estimated for the benzene clathrate and desolvated samples, respectively.

23 namics of the phenylene group in the benzene clathrate and in desolvated samples were characterized i

24 uid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals.

25 ng indices for the three methylcyclohexanone clathrates and their respective desolvation onset temper

26 could amorphous nuclei grow into crystalline clathrates and, second, whether amorphous nuclei are int

27 ture were remarkably similar to those in the clathrate, and both are among the fastest known for phen

28 the nucleus on the subsequent growth of the clathrates, and found that both amorphous and sI crystal

29 ation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mant

30 er long edge, 177-nanometer short edge) into clathrate architectures.

31 y averaged Raman spectra of H(2) in hydrogen clathrate are calculated by quantum-mechanical calculati

32 Semiquantitative phase diagrams of 2D clathrates are constructed where representative patterns

33 heory (DFT) calculations show that all three clathrates are energetically stable with relaxed lattice

34 Clathrates are guest/host framework compounds composed o

35 Three-dimensional (3D) gas clathrates are ice-like but distinguished from bulk ices

36 Clathrates are open crystals in which molecules are arra

37 s indicate that the boron-substituted carbon clathrates are stabilized under high-pressure conditions

38 innovative experiments for synthesizing the clathrate as a hydrogen storage medium.

39 1.2 A(3) at 1.1 GPa) and 45 +/- 5 GPa for Xe clathrate B (tetragonal, a = 8.320 +/- 0.004 A, c = 10.2

40 cture I (A) and the discovery of a second Xe clathrate (B) above 1.8 GPa have implications for xenon

41 ssion electron microscopy indicated that the clathrate Ba8Au16P30 is well-ordered on the atomic scale

42 New clathrate-based phase-change materials with cage-like st

43 s not only brings new insights into hydrogen clathrates but also refreshes the perspective of clathra

44 The clathrate cages are multiply occupied, with a cluster of

45 eviously unreported H(24) and H(30) hydrogen clathrate cages at megabar pressures.

46 th the dilute solution and give birth to the clathrate cages that eventually transform it into an amo

47 y potentially be substituted within Type-VII clathrate cages, presenting opportunities for a large fa

48 presence of both sodium and hydrogen in the clathrate cages.

49 Notably, the formation of 2D amorphous clathrate can occur over a wide range of temperatures, e

50 Our results reveal that clathrate can store up to four hydrogen molecules in eac

51 erable hydrogen is stored molecularly within clathrate cavities as well as chemically in the clathrat

52 1 wt % hydrogen may be stored in the beta-HQ clathrate cavities.

53 CH3CH2OH, CH3CN, CH3NO2, I2), and a propyne clathrate (CH3CCH@Me,H,SiMe2.2CHCl3), have been prepared

54 on of [(TMA)(x) (Q(3) (8) ).n H(2) O]((x-8)) clathrate complexes into step edges on the crystals.

55 ystal growth unveiled that instead of type-I clathrates, compositionally close but structurally diffe

56 This is the first example of a clathrate compound where the framework atoms are not in

57 ctural complexity in compositionally similar clathrate compounds indicates that the reaction path may

58 This clathrate consists of a 3D Zn-Sb framework hosting K(+)

59 4CH4) should distinguish between wetland and clathrate contributions to this increase.

60 CH4-C2H6 ocean and between the ocean and the clathrate crust beneath, fractionation which occurred du

61 nuclei are intermediates in the formation of clathrate crystals for temperatures close to equilibrium

62 ds into seven different host-guest colloidal clathrate crystals with unit cells ranging from 84 to 36

63 n from an amorphous glassy phase, as well as clathrate crystals, leaving a narrow widow of patch widt

64 Subsequent to clathrate decomposition, the host HQ was used to directl

65 energy, supplied at depth as latent heat of clathrate decomposition, to shallower levels, where it r

66 etween ice-sheet-derived meteoric waters and clathrate-derived fluids during the flushing and destabi

67 tedly during the last glacial cycle involves clathrate destabalization events.

68 As a consequence, although clathrate destabilization may or may not have had a role

69 at may indeed form but participate in floppy clathrates, eventually have to give way to cagelike poly

70 ure composed of heavy elements, the reported clathrates exhibit ultralow thermal conductivities of le

71 subtle aspects of the model and to intrigue clathrate experts with a fresh look on this well-establi

72 hermal conductivity, a unique feature of the clathrate family of compounds.

73 during the flushing and destabilization of a clathrate field by glacial meltwater.

74 structed where representative patterns of 2D clathrates for characteristic gas molecules on prototypi

75 RPD spectra of even larger clusters, such as clathrates, for which precise mass selection of neutral

76 ortant decrease of the pressure required for clathrate formation (approx. 20%) compared to the pure H

77 The kinetic process of 2D clathrate formation is illustrated via simulated single-

78 The underlining physical mechanism for 2D clathrate formation on superhydrophilic surfaces is eluc

79 is fundamentally important to understanding clathrate formation, structure stabilization and the rol

80 gesting a strong densification effect of the clathrate framework on the enclosed hydrogen molecules.

81 In the clathrate framework, a full ordering of {Ga or In} and S

82 pectrum is consistent with phase pure type I clathrate framework.

83 ant source of stability for the structure-II clathrate framework.

84 Clathrates (gas hydrates) are water-based (ice-like) str

85 stable than without FTP present suggesting a clathrate guest-host association with the FTP.

86 structural x(gas/guest)@Me,H,SiMe2 (x </= 1) clathrates (guest = H2O, N2, Ar, CH4, Kr, Xe, C2H4, C2H6

87 The activation (emptying) of several clathrates (guest = H2O, N2, CO2, Kr, CH3F) is shown to

88 ree-dimensional hydrogen network composed of clathrate H(29) cages.

89 ate I), 7Li@C33B7 (Clathrate IV), 6Li@C28B6 (Clathrate H), and 6Li@C28B6 (Clathrate II) are definitel

90 In bulk, pure hydrogen clathrate (H(2)O-H(2)) only forms in harsh conditions, b

91 us far, experimental evidence for guest-free clathrates has only been found in germanium and silicon,

92 arming, triggered by release of methane from clathrates, has been postulated to have occurred during

93 Because marine clathrates have a distinct deuterium/hydrogen (D/H) isot

94 ium and silicon, although guest-free hydrate clathrates have been found, in recent simulations, able

95 ly water is required to construct the cages, clathrates have been identified as a potential solution

96 pace filling by gas molecules, standalone 3D clathrates have not been observed to form in the laborat

97 thrate cavities as well as chemically in the clathrate host material.

98 oposed exchange mechanism is consistent with clathrate hydrate being an equilibrium system in which g

99 n industrial applications to prevent methane clathrate hydrate blockages from forming in oil and gas

100 y unverified role for methanol as a guest in clathrate hydrate cages.

101 hydrates and participates synergistically in clathrate hydrate formation in the presence of methane g

102 ly predicting the equilibrium conditions for clathrate hydrate formation is crucial.

103 ce the chemistry of low dosage inhibitors of clathrate hydrate formation within the context of their

104 "Craigite," the mixed-air clathrate hydrate found in polar ice caps below the dept

105 tate the heterogeneous nucleation of methane clathrate hydrate from an aqueous methane solution.

106 Carbon monoxide clathrate hydrate is a potentially important constituent

107 ia, and binary structure I ammonia + methane clathrate hydrate phases synthesized have been character

108 Compared with water-based clathrate hydrate phases, the beta-HQ+H2 clathrate shows

109 A unique clathrate hydrate structure, previously known only hypot

110 n, dissociation, and reactivity of argon gas clathrate hydrate was investigated by time-of-flight neu

111 We synthesized a hydrogen clathrate hydrate, H(2)(H(2)O)(2), that holds 50 g/liter

112 ing a suitable nano-confinement for ice-like clathrate hydrate.

113 ated the stability of nano-confined hydrogen clathrate hydrate.

114 interactions between the CO(2) molecules and clathrate hydrate/H(2)O frames.

115 Clathrate hydrates (CHs) are ubiquitous in earth under h

116 We turn our focus to clathrate hydrates and discuss the major contributions t

117 Like other clathrate hydrates and forms of ice, the protons of H2O

118 al planetary atmospheres, that ammonia forms clathrate hydrates and participates synergistically in c

119 pological dual relations between networks of clathrate hydrates and tetrahedral close-packed structur

120 metastable formation of sII CO(2) and CH(4) clathrate hydrates and their slow conversion to sI under

121 Clathrate hydrates are a class of ordered structures tha

122 Clathrate hydrates are crystalline solids characterized

123 Clathrate hydrates are predicted to form by virtually th

124 Clathrate hydrates are specific cage-like structures for

125 hrates but also refreshes the perspective of clathrate hydrates as hydrogen storage media.

126 ed structures, the descriptors presented for clathrate hydrates can be directly extended to other ord

127 of vapor-deposited amorphous ices in vacuo, clathrate hydrates can form by rearrangements in the sol

128 However, how clathrate hydrates can form in low-pressure environments

129 The presence of clathrate hydrates in cometary ice has been suggested to

130 t to contribute to the outgassing of methane clathrate hydrates into these moons' atmospheres.

131 uring the formation of bulk and nanoconfined clathrate hydrates occluding methane, ethane, and hydrog

132 The nucleation and growth of clathrate hydrates of a hydrophobic guest comparable to

133 The formation of clathrate hydrates offers a powerful approach for separa

134 pontaneous formation of two-dimensional (2D) clathrate hydrates on crystal surfaces without conventio

135 ge and description of guest molecules within clathrate hydrates only accounts for occupancy within re

136 Clathrate hydrates reserved in the seabed are often disp

137 ies near ambient conditions, the most stable clathrate hydrates should be identified.

138 termediates are involved in the formation of clathrate hydrates under conditions of high driving forc

139 the many studies that have been performed on clathrate hydrates, the actual molecular mechanism of bo

140 ay to understand the intricate structures of clathrate hydrates, which unveils the diverse crystallin

141 o guest-guest and guest-host interactions in clathrate hydrates, with potential implications in incre

142 ration shells were thought to resemble solid clathrate hydrates, with solutes surrounded by polyhedra

143 o both large and small cages of structure II clathrate hydrates.

144 er molecules making up the crystalline solid clathrate hydrates.

145 ustrate the rich structural possibilities of clathrate hydrates.

146 lly accepted because of skepticism about the clathrate hydration shell.

147 recent theory-driven discovery of a class of clathrate hydrides (e.g., CaH(6), YH(6), YH(9), and LaH(

148 f a unique class of thermodynamically stable clathrate hydrides structures consisting of two previous

149 The clathrate I modification exists for the same composition

150 res of 2Li@C10B2 (Clathrate VII), 8Li@C38B8 (Clathrate I), 7Li@C33B7 (Clathrate IV), 6Li@C28B6 (Clath

151 gher density of the clathrate VIII type than clathrate I, opening up the perspective of obtaining cla

152 III type compounds as high-pressure forms of clathrate I.

153 allizes in an orthorhombic superstructure of clathrate-I featuring a complete separation of gold and

154 crystallize in an ordered superstructure of clathrate-I in the Ia3 space group (No.

155 we show experimental evidence of guest-free clathrate-I Si(46) framework from Ba(8-x)Si(46) under in

156 The guest-free monolayer clathrate ice is a low-density ice (LDI) whose geometric

157 idence of spontaneous formation of monolayer clathrate ice, with or without gas molecules, within hyd

158 ts the first thermodynamically stable type-I clathrate identified and suggests that boron-substituted

159 IV), 6Li@C28B6 (Clathrate H), and 6Li@C28B6 (Clathrate II) are definitely stabilized in theoretical c

160 The synthesis and single crystal growth of clathrate-II Na(24)Si(136) is performed in one step appl

161 lso observed between C(6)D(6) and the liquid clathrate ionic complexes, [Hg(arene)(2)(MCl(4))][MCl(4)

162 a) in all the three structures generate A136 clathrate-IotaIotatype networks with remarkably specific

163 structure of the Ba8 M24 P28+delta (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra comm

164 The quenched clathrate is stable up to 145 kelvin at ambient pressure

165 driving force for the formation of this new clathrate is the excess of electrons generated by a high

166 The stored hydrogen is released when the clathrate is warmed to 140 K at ambient P.

167 to the atmosphere through destabilization of clathrates is a positive feedback mechanism capable of a

168 A tunable pattern of 2D amorphous clathrates is demonstrated by changing the lattice strai

169 framework structure, the current research on clathrates is focused on finding the ones with large the

170 Since the thermal conductivity of clathrates is inherently small due to their large unit c

171 at the dissociation temperature of amorphous clathrates is just 10% lower than for the crystals, faci

172 y near the energy band edges for Si(46)-VIII clathrates is responsible for the formation of such a la

173 pleted carbon source, such as marine methane clathrates, is therefore not required.

174 te VII), 8Li@C38B8 (Clathrate I), 7Li@C33B7 (Clathrate IV), 6Li@C28B6 (Clathrate H), and 6Li@C28B6 (C

175 e analyzed computationally in the context of clathrate-like alkali metal cation hydrates, including C

176 shell near flat surfaces fluctuates between clathrate-like and less-ordered or inverted structures.

177 O) molecule embedded at various sites in the clathrate-like cage structure adopted by the Cs(+).(D(2)

178 excess proton is embedded on the surface of clathrate-like cage structures with one or two water mol

179 d H3O(+) moiety embedded on the surface of a clathrate-like cage.

180 ionally close but structurally different new clathrate-like compounds formed, Ba(2)Zn(5)As(6) and Ba(

181 hat are orientationally inverted relative to clathrate-like hydration shells, with unsatisfied hydrog

182 atures (T(c) s) of metal hydride phases with clathrate-like hydrogen networks have generated great in

183 y of superconducting hydrides that possess a clathrate-like structure in which the host atom (calcium

184 For clathrate-like structure to be evident, the distribution

185 , whereas another one results in a colloidal clathrate-like structure, in both cases without any inte

186 ry hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic prop

187 surface topography of the melittin molecule: clathrate-like structures dominate near convex surface p

188 hydrophobic headgroups creating ice-like or clathrate-like structures in the surrounding water, alth

189 One component may be a clathrate-like water cluster near the hydrophobic cholin

190 t the ice-binding surface, and stabilize the clathrate-like water in the anchored clathrate motif tha

191 role of the hydroxyl groups is to anchor the clathrate-like water through direct hydrogen-bonding, po

192 ration shell of small hydrophobic solutes is clathrate-like, characterized by local cage-like hydroge

193 Clathrate materials have been the subject of intense int

194 d and suggests that boron-substituted carbon clathrates may represent a large family of diamond-like

195 ses controlling the formation of this liquid clathrate might help to tailor other catalysts and subst

196 elow the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2

197 evelopment of a phenomenological approach to clathrate modeling.

198 ize the clathrate-like water in the anchored clathrate motif that binds these proteins to ice.

199 lity for additional tetrahedral carbon-based clathrate networks, more than 5000 unique boron decorati

200 Here we show a clathrate (non-porous) coordination network that undergo

201 cluster and local structuring hypotheses of clathrate nucleation and bears strong analogies to the t

202 lity and growth of amorphous and crystalline clathrate nuclei and assess the thermodynamics and kinet

203 at eventually transform it into an amorphous clathrate nucleus.

204 ion structures were obtained for an o-xylene clathrate of 2 and for solvent-free crystals of 3.

205 stabilities of a series of xenon and krypton clathrates of (+/-)-cryptophane-111 (111).

206 can be arrested in the metastable amorphous clathrate phase for times sufficiently long for it to ap

207 e caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.

208 at which pressure it transforms to a new Xe clathrate phase stable up to 2.5 GPa before breaking dow

209 This material is synthesized as a clathrate phase with solvent-filled cavities; evacuation

210 A novel clathrate phase, Ba8Au16P30, was synthesized from its el

211 coexisting cubic Fm3 m and hexagonal P63/mmc clathrate phases observed over the pressure range from 1

212 switching between guest-free and gas-loaded clathrate phases.

213 These clathrates represent the first examples of tetrel-free c

214 creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by t

215 ion in the interior and at the surface of a clathrate, respectively.

216 We expect this review to help newcomers to clathrate science in elucidating some subtle aspects of

217 l as holding fundamental interest, molecular clathrates serve practical purposes, such as for gas sto

218 The X-ray crystal structure of the clathrate shows an increased torsion angle between the a

219 sed clathrate hydrate phases, the beta-HQ+H2 clathrate shows remarkable stability over a range of p-T

220 aordinarily large power factor for type-VIII clathrate Si(46).

221 ctors, Mg2Si, Si0.8Ge0.2, Al(x)Ga(1-x)As and clathrate Si46-VIII were studied, which showed different

222 he 60-year anniversary of the publishing of "Clathrate Solutions" by van der Waals and Platteeuw in 2

223 gies have been analyzed and show that liquid clathrate solvation of the transition state is primarily

224 Clathrate stability is maximized when the boron atoms ar

225 host-guest ratio is similar to the cubic Xe clathrate starting material.

226 The type I clathrate structure has two types of cages where the gue

227 The extended pressure stability field of Xe clathrate structure I (A) and the discovery of a second

228 a type-I carbon-based framework-a ubiquitous clathrate structure type found throughout compounds cont

229 ecules and phenylene groups suggested by the clathrate structure was investigated.

230 CeH(9) crystallizes in a P6(3)/mmc clathrate structure with a very dense 3-dimensional atom

231 H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar rat

232 The term "clathrate structure" is quantified for solvation of nonp

233 Sr, La) compounds in the bipartite sodalite clathrate structure, density functional theory (DFT) cal

234 pressure, and adopts the known open-network clathrate structures (sII, C(0)), dense "filled ice" str

235 free O-H stretch region are consistent with clathrate structures for the MNCs with 20 water molecule

236 compound, crystals grown from benzene formed clathrate structures in the space group Ponemacr; with o

237 r, there is no evidence for the formation of clathrate structures seen recently via IR spectroscopy o

238 nts a promising approach to stabilize carbon clathrate structures, but no thermodynamically stable su

239 s, from the very large number of conceivable clathrate structures, only a small fraction of them have

240 ealization of hot superconductors in ternary clathrate superhydrides.

241 Analyte materials adsorbed onto this 'clathrate' surface are subsequently released by laser ir

242 The clathrate, synthesized at 200-300 MPa and 240-249 K, can

243 eaction to the transient formation of liquid clathrate that contains a few molecules of the substrate

244 represent the first examples of tetrel-free clathrates that are completely composed of main group el

245 conducive to the formation of heteronetwork clathrates that are stable both thermodynamically and ki

246 rent from the arrangement found in CH4/water clathrates, the CH4 store of nature.

247 crystallized in the presence of all of these clathrates, the dimeric macrocycles result in all cases,

248 s have been release and uptake of methane by clathrates, the positive correlation between temperature

249 Inside the cages of hypothetical carbon clathrates there is precious little room, even for the s

250 ethane released from low-latitude permafrost clathrates therefore acted as a trigger and/or strong po

251 Finally, we present some of the areas in clathrate thermodynamics that we foresee as the new fron

252 an enticing goal with only two alkali metal clathrates to date, Cs(8)Zn(18)Sb(28) and K(58)Zn(122)Sb

253 cules trapped in nanostructured surfaces or 'clathrates' to release and ionize intact molecules adsor

254 In a second step, the amorphous clathrate transforms into crystalline clathrate.

255 A new clathrate type has been discovered in the Ba/Cu/Zn/P sys

256 -ray diffraction data is consistent with the clathrate type I structure.

257 micelle size dispersity, leading to complex clathrate type structures in multilayer superstructures.

258 itu powder X-ray diffraction yielded a novel clathrate type XI K(58) Zn(122) Sb(207) .

259 Toward this, Si(46) clathrate type-I crystals containing alkali/alkaline-ear

260 ages, some of which are reminiscent of known clathrate types while others are unique to this structur

261 tal evidence for rapid formation of hydrogen clathrates under mild pressure and temperature condition

262 Hydrogen within the beta-HQ clathrate vibrates at considerably lower frequency than

263 The resulting structures of 2Li@C10B2 (Clathrate VII), 8Li@C38B8 (Clathrate I), 7Li@C33B7 (Clat

264 e I, opening up the perspective of obtaining clathrate VIII type compounds as high-pressure forms of

265 licide crystallizing in the rarely occurring clathrate VIII type structure.

266 adaptions allow for a higher density of the clathrate VIII type than clathrate I, opening up the per

267 for bacteria and climate-related changes in clathrate volume represent positive feedbacks for climat

268 The crystal structure of this new clathrate was determined by a combination of X-ray and n

269 Structure I xenon clathrate was observed to be stable up to 1.8 GPa, at wh

270 as hydrate lattice through the same anchored clathrate water mechanism used to bind ice.

271 The internal clathrate water network of the fish AFP Maxi, which exte

272 bon hydration shells are formed, possibly of clathrate water, and they explain why hydrocarbons have

273 dues (matched to the ice lattice) that order clathrate waters into an ice-like structure(6).

274 Crystals of a benzene clathrate were characterized by single crystal X-ray dif

275 ither in the interior or at the surface of a clathrate were determined by comparing IRPD spectra of t

276 d one stadial period, suggesting that marine clathrates were stable during these abrupt warming episo

277 Ordered assemblies, isostructural to clathrates, were identified with the help of molecular s

278 protonated ammonia is in the interior of the clathrate, whereas protonated methyl- and n-heptylamine

279 host, but also to the crystal packing of the clathrate, wherein each window of the molecular containe

280 mensional analogue of the well-known Hofmann clathrates which is formed through axial bridging of the

281 The synthesized clathrate, which is recoverable to ambient conditions, e

282 A hydrogen-encapsulated inorganic clathrate, which is stable at ambient temperature and pr

283 ommodation, and the kinetic stability of the clathrates, which has been probed by thermal gravimetric

284 modynamic path to grow a new form of methane clathrate whose BL ice framework exhibits the Archimedea

285 p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is consi

286 We report a carbon-boron clathrate with composition 2 La@B(6) C(6) (LaB(3) C(3) )

287 the formation of beta-hydroquinone (beta-HQ) clathrate with molecular hydrogen.

288 revalence among tetrahedral network formers, clathrates with a carbon host lattice remain unrealized

289 omputationally for type-I and type-II carbon clathrates with a range of guest elements including Li,

290 onding theory to design host-guest colloidal clathrates with explicit interparticle attraction, provi

291 rge family of boron-stabilized, carbon-based clathrates with ranging physical properties.

292 104) has been the sole representative of tin clathrates with the type II structure.

293 Three novel unconventional clathrates with unprecedented III-V semiconducting frame

294 cubic bipartite sodalite structure (Type-VII clathrate) with La atoms encapsulated within truncated o

295 l that solvent molecules intercalate or form clathrates within the molecular pockets of CBI-35CH at l

296 The electron-precise composition of this clathrate yields narrow-gap p-type semiconductor with ex